Airplane Flight Manual DA 42 TDI

lot (and accident investigator) training manuals do not adequately present the associated control and performance limitations of engine-out flight which the airplane design engineers used during designing the airplane and test pilots determined during flight-testing. 1.5. The DA 42 AFM was reviewed out of curiosity on the subject of engine failure, after downloading from the website of DIAMOND AIRCRAFT INDUSTRIES GMBH8. This manual might be a little dif- ferent from the one that applies to the mishap airplane. The downloaded AFM has been verified for EASA by the Austrian Civil Aviation Authority Austro Control (ACG) as Primary Certification Authority (PCA) in accordance with the valid Certification Procedures, and approved by EASA with approval no. 2004-4703. It is also approved by the FAA for U.S. registered aircraft, and is required by FAA Type Certificate Data Sheet (TCDS) A57CE. These authoritative reviews were re- grettably inappropriate as well, as will be shown in this review below. 1.6. This review is not to apportion blame or liability to anybody, but to alert/make aware/ teach/ learn from, which is necessary because appropriate knowledge obviously just faded away during the past 50 years or so, and fatal accidents with multi-engine airplanes, not only with the DA 42, continue to happen quite frequently. For this reason, explanations are included as well as recom- mendations for improvement. This review might also apply to the AFM of the other airplane types of the manufacturer, and to AFMs of other airplane manufacturers as well, because most of the errors are commonly made for the reason given in the paragraphs above, which include the use of the GAMA Specification No. 1. If the review of certain subjects below is not adequate, the subjects might not have been de- scribed properly (for a non-DA 42 pilot). 1.7. Conclusions and recommendations. The writers of the DA 42 AFM used the deficient GAMA Specification No. 1 and obviously also had a disappointing understanding of airplane speeds, per- formance, control, and of applicable paragraphs in airworthiness regulations CS/FAR 23 them- selves. Their AFM does not provide pilots with appropriate data and procedures to prevent fatal accidents after engine failure, as required by CS and FAR 23. The verification of the AFM on be- half of EASA and FAA was not adequate; the AFM does not comply with their own Regulations and Flight Test Guides. The DA 42 AFM should not have been approved, just like AFMs of other manufacturers who used GAMA Specification No. 1. Improper pilot manuals which are written, 5 Website AvioConsult, Links page with links to USArchives downloads: https://www.avioconsult.com/links.htm. 6 GAMA Specification No. 1, Specification for Pilot's Operating Handbook, Rev. No. 2, 1996, https://gama.aero/facts-and-statis- tics/consensus-standards/publications/gama-and-industry-technical-publications-and-specifications/. 7 Limited Review of GAMA Specification No. 1 for Pilot's Operating Handbook, https://www.avioconsult.com/down- loads/GAMA Specification No.1 for Pilot's Operating Handbook, Limited Review.pdf. 8 Airplane Flight Manual DA 42 TDI Basic Rev. 9 2022-01-17. http://support.diamond-air.at/fileadmin/uploads/files/af- ter_sales_support/DA42_Twin_Star/Airplane_Flight_Manual/Basic_Manual/70105e-Rev9-complete.pdf. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 3 reviewed, and approved by incompetent writers and authorities cause aviation to drift into fail- ure. 1.8. The use of Calibrated and Indicated Airspeeds (CAS, IAS) and the definitions thereof, including of the minimum control speed VMCA and the accompanying manoeuvre limitations in the Specifica- tion, are incorrect and not in compliance with EASA Certification Specifications (CS) 23 / and FAA Federal Aviation Regulations (FAR) 23. IAS should not be used in an AFM. 1.9. The proposed engine emergency procedures do not include the most important associated con- trol limitation that pilots should observe to prevent the loss of control, especially during take-off, approach for landing, and go-around. The consequence is that pilots, without realizing, manoeu- vre their airplane after engine failure in a way for which it was not designed and flight tested, and subsequently lose control and get killed, taking their crew and passengers with them. Pilots have the right to be provided with an excellent AFM, developed with the highest level of expertise available in the industry and containing the proper guidance for operating their air- plane safely. 1.10. The manufacturer is strongly recommended to improve the AFM. EASA, FAA and equivalent organizations are recommended to improve the knowledge of person- nel tasked with reviewing and approving AFM and pilot training manuals and training proce- dures. Accident investigators are recommended to include a thorough review of AFM/POH and pilot training material during accident investigations. A pilot license alone is not the confirmation of an adequate level of aeronautical knowledge to write and/or review AFMs, or to investigate accidents; a multi-disciplinary team of highest level of educated experts on the subjects of flying, airplane performance, flying qualities, aeronautical engineering, and human factors is required to do so. 2. Airspeeds Explained 2.1. During reviewing the DA 42 AFM (and other POH/AFMs prepared using GAMA Specification No.1), the use of Calibrated Air Speeds (CAS) and Indicated Air Speeds (IAS) was found to be nei- ther in compliance with the way these airspeeds are defined and used in Airworthiness Standard 14 CFR FAR 239 and equivalent, nor as used during airplane design as taught at aeronautical uni- versities10, and nor as taught at test pilot schools for experimental flight testing, including the calibration of pitot-static systems. AFM-writers, approving authorities, and pilots seem to strug- gle with understanding why these airspeeds exist and what their function is. Therefore, a few general remarks are presented prior to reviewing the AFM to become aware of the real values of the used airspeeds. Misuse of the CAS and IAS in an AFM led and still leads to fatal accidents, as will become clear in this review. Reference is made to the applicable aviation and other regula- tions; the source of the remarks below is the Pitot-Statics and the Standard Atmosphere course book of the USAF Test Pilot School11 that is approved for public release and available for down- load from the US Archives. Instructors of test pilot schools teach and conduct pitot-static system testing, i.e. airspeed system calibrations, at least 50 times each year to and with the students; they know what they are talking about, and share their knowledge to learn from. 2.2. The True, Calibrated, and Indicated Airspeeds of an Airplane 2.2.1. Pilots need to know what the airspeed of their airplane is, not only for navigation pur- poses, but also for the piloting task, and to use operational speeds and observe limiting speeds. Complicating is that the airplane operates in a moving atmosphere at altitudes between ground level and the maximum operating altitude of the airplane. The temperature and air pressure in the atmosphere, also called density, change during the day and with altitude, and have effect on 9 Code of Federal Regulations, Title 14, Chapter I, FAR 23, 1−1−10 Edition was used in this review. Link to 2017 version: https://www.ecfr.gov/on/2017-01-03/title-14/chapter-I/subchapter-C/part-23/subpart-B. 10 Stability and Control during Steady Straight Flight, Airplane Design Part VII, Dr. Jan Roskam, DAR Corporation, Kansas: https://shop.darcorp.com/index.php?route=product/category&path=60 11 Pitot-Statics and the Standard Atmosphere, 4th edition (July 2020), Russell E. Erb, USAF Test Pilot School, https://apps.dtic.mil/sti/pdfs/AD1115005.pdf. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 4 the performance of engines, on the aerodynamic (control) surfaces of the airplane, and on meas- uring the airspeed. Four speeds that are in use today are briefly explained, and in addition also the Minimum Con- trol Speed VMC(A), because this limiting speed, that applies in anticipation of and following an en- gine failure, is misunderstood by most pilots, leading to accidents. 2.2.2. True Air Speed (TAS, or Vt) is the airspeed (velocity) at which the airplane is plowing the air mass which is not yet disturbed and influenced by the airplane (e.g. its bow wave), and which generates the aerodynamic lift and control power with respect to the ambient pressure and tem- perature (at the flying altitude). TAS is not useful for the piloting task, i.e. for control and performance, because of the influence of ambient temperature and altitude (density − ρa and Pa in Figure 1); the use of TAS would re- quire computing different speeds for each combination of ambient temperature and altitude. In addition, it is quite complicated to build an accurate mechanical TAS indicator to account for the temperature and altitude effects, which was the reason to introduce the Cali- brated Air Speed (CAS), for which the standard atmos- pheric pressure and temperature at sea level are used as a reference, rather than the ambient pressure and temperature at flight altitude. CAS makes the piloting task and the use of pre-determined and flight-test acquired performance data, operational, and limiting speeds more convenient. TAS is the airspeed used by pilots for the navigation task, for calculating the speed and time en- route and is calculated from CAS using both the actual ambient pressure altitude and the outside air temperature, using a flight computer (E6-B), or by an on-board computer. A proper definition of True Airspeed (TAS) is: TAS is the true airspeed of the airplane in undisturbed air with respect to the ambient pressure and temperature As the standard atmospheric pressure and density (temperature) at sea level were used as refer- ences for the CAS, TAS is equal to CAS at sea level in a standard atmosphere. 2.2.3. Calibrated Air Speed (CAS, or VC) is the airspeed (velocity) of the airplane in the undis- turbed free airstream with reference to standard atmospheric pressure and temperature at sea level, as explained in the previous paragraph. The air pressures that are representative of the speed should be sensed by a long pitot-static boom that sticks out in front of the bow wave, which is not always practical. Therefore, the total pressure (PT) is sensed by a pitot tube mounted on fuselage or wings in disturbed air and the ambient (static) pressure (Pa or PS) by one Figure 1. True Airspeed (TAS, Vt) equation. Figure 2. A common pitot-static system and its errors; from CAS in undisturbed airstream to IAS on the ASI. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 5 or two flush ports, as shown in Figure 2 above. Both air pressures are fed into an Air Speed Indi- cator (ASI) which is constructed to sense the differential pressure PT – Pa and indicate the corresponding cali- brated airspeed (which occurs when the errors are zero) with respect to the standard atmospheric pressure and density at sea level (PSL respectively ρSL in Figure 3), which are the references for CAS. The only variable is the differential pressure PT – Pa. At a constant differential pressure, the CAS will always be the same. Changes in sea level pres- sure and temperature will not affect CAS. Hence, CAS on one day is CAS on another day. There- fore, CAS is convenient for the piloting task (as compared to TAS); the AFM-published speed limi- tations such as VS, VMC, and VMO, and operational speeds such as V1, VR, V2 and VREF are propor- tional to CAS for a given gross weight. CAS is also used to present performance data in an AFM. CAS in one airplane is CAS in another airplane of the same type. The CAS of two airplanes flying in formation should be equal. CAS is often inappropriately explained as being the abbreviation of Computed Air Speed, even by accident investigators. 2.2.4. The definition of CAS in an AFM is almost always how to calculate CAS from IAS, like GAMA inappropriately recommends in Specification No.1: "Calibrated Airspeed means the indi- cated airspeed of an airplane corrected for position and instrument error". CAS is indeed IAS cor- rected for instrument and position error, in this order though, but CAS "means" much more. CAS is used during flight-testing to determine and report limiting and operational speeds, and perfor- mance data. The use of CAS allows the manufacturer or operator to use (copies of) the same POH/AFM for a series of airplanes of the same type that have identical pitot-static systems (posi- tion errors). The FAA or equivalent authority then must approve only one AFM. Finally, CAS is the origin of the other airspeeds and deserves a better, appropriate, and explaining definition. Therefore, the definition of Calibrated Airspeed (CAS) should be: CAS is the calibrated airspeed in undisturbed air with respect to the standard atmospheric pressure and temperature at sea level 2.2.5. Errors in the Pitot-static system. Prior to explaining Indicated Airspeed, the pitot-static system errors (Figure 2) need some clarification. The system errors consist of position, lag, and instrument errors which will be discussed briefly. 2.2.5.1. Position Error. The consequences of positioning the pressure sensors in dis- turbed air and flush on the fuselage are errors in the pressure measurements, called po- sition errors. The error is influenced by the local pressures at the pitot-tube and flush port(s) due to changing angle of attack and angle of sideslip and hence, depends on air- plane configuration, airspeed, weight, and altitude. FAR § 23.1323 (b) determines: "the pitot-static system error, excluding the ASI calibration error, to not exceed the maximum of 3% of CAS or 5 kt". Position errors are determined during in-flight calibration for sev- eral configurations (flaps, gear, weight) over a range of airspeeds and altitudes and are furnished in graphs in the AFM for use by pilots. 2.2.5.2. Instrument Errors. An ASI has errors too, called instrument errors, as shown in Figure 2 and requires calibration as well. Calibration of both the pitot-static system and the ASI gave the calibrated airspeed its name; CAS is the airspeed with maximum obtain- able accuracy (for subsonic flight). The expansion of the aneroid (diaphragm or bellows) within a mechanical ASI due to the difference between PT and PS (= Pa) is translated by mechanical parts to the pointer of the ASI which rotates above an airspeed scale indicat- ing the IAS. The mechanism in the ASI is designed and constructed to indicate the air- speed with respect to the standard atmospheric pressure and temperature (ISA) at sea level (CAS equation in Figure 3). The errors between the air pressures PT and Pa at the entrance ports of the ASI and the eyes of the pilot(s), caused by the mechanical parts within the ASI, such as Figure 3. Calibrated Airspeed (CAS, Vc) equation. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 6 manufacturing discrepancies, magnetic fields, hysteresis or friction, altitude, tempera- ture changes, vibration, inertia of moving parts, and the parallax, contribute to the total instrument error. The instrument error of each individual ASI over a range of airspeeds is determined in an instrument laboratory during calibration at sea level in a standard atmosphere, as required by FAR § 23.1323(a). SAE AS 8019 presents detailed ASI specifi- cations, but this document is not freely accessible. In another AFM, the permissible in- strument error is mentioned to be ± 4 kt at speeds above 50 kt. In addition, the friction of the pointer "must not produce an error exceeding 3 kt". Hence, in a worst-case situation, the difference between the IAS indicated on two ASIs connected to the same pitot-static system is allowed to be up to 8 kt (if one error hap- pens to be – 4 kt and the other + 4 kt) while the CASs, calculated after adding the known instrument correction of each ASI and the (common) position error correction of the pi- tot-static system are equal. 2.2.5.3. The pressure difference PT minus Pa (or PS) at the entrance of the ASI is a measure of the IAS plus or minus the instrument error, and is also called the instrument corrected airspeed Vic (Figure 2), which is to be used as the entry variable for the posi- tion error chart in the AFM when calculating CAS from IAS. 2.2.5.4. Lag errors. The pressure lag errors are caused by the friction, the pressure drop, and the inertia of the air mass in the air tubes causing a small delay, but are con- sidered not to have influence except when changing airspeed or altitude. These errors will not be further discussed. 2.2.5.5. Errors in Electronic Air Data systems and displays. Modern air data systems do not have a mechanical ASI anymore (except for a backup/ alternate). Such a system however, still has the errors as shown in Figure 2. Pressure transducers in the air data system convert the analog air pressures PT and PS into digital output data for further processing and display. Besides analog to digital conversion errors, also drifting of the output can occur over time; fluctuations of electrical power supply voltage, equipment temperature might affect the output data as well. Such an air data system would require calibration, which might include both pitot-static position and “instrument” calibrations, of which the result could be entered in the computerized air data system for correcting the errors. Then the airspeed indicated on the ASI (speed tape) has become the CAS of the airplane, the only relevant, accurate speed for the piloting task which is also the only airspeed that should be used in the POH/AFM. The piloting task becomes more conven- ient. In most older airplanes though, the pilot must still work with both the position and instrument errors and hence with both CAS and IAS. 2.2.5.6. Total system error. The sum of both position and instrument errors comprises the relationship between CAS and IAS. FAR § 23.1587(d)(10) requires this relationship to be furnished to the pilot for commuter category airplanes. The maximum regulations- approved airspeed error, being the sum of the approved instrument and position errors, is in a worst case allowed to be as high as (4 + 5 =) 9 kt (FAR § 23.1323(b) and SAE AS 8019). An additional friction error of up to 3 kt might occur during acceleration (takeoff) or deceleration. These are numbers that a pilot needs to be made aware of for being able to plan and conduct the takeoff, approach, and landing safely, and for handling the airplane, including in case one engine fails or is inoperative. 2.2.5.7. Hence, the airspeed indicated by the pointer of the (mechanical) ASI is not the CAS anymore; the inherent system errors (Figure 2) affect the air pressures PT and Pa en- route from the undisturbed air ahead of the airplane to the ASI, and the conversion of the air pressures within the ASI up to the pointer. Hence, CAS cannot be directly indi- cated in the cockpit but must be calculated by the pilot by adding both the pitot-static position error and the ASI instrument error to the airspeed indicated by the Airspeed Indicator (ASI), and the results written on a Takeoff and Landing Data card, or by posi- tioning bugs on the ASI. The errors can be positive, zero or negative. Backwards, when Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 7 the pilot needs performance data out of the AFM while in-flight, IAS values read from the ASI need to be corrected with the instrument error (=Vic), which is then used to find the position error to be added to calculate the CAS required to enter the performance graphs in the AFM. 2.2.6. The Indicated airspeed (IAS) is the speed indicated or displayed on an Airspeed Indicator (ASI), which is the CAS including the inherent pitot-static position and instrument errors (Figure 2), and hence is not the airspeed anymore at which the airplane moves through the air. IAS is a speed that is not directly useful for pilots, however, it is the only speed that the pilot can work with, but it needs corrections to become a valuable airspeed. IAS exists because an ASI is simple in design and construction and is easy to calibrate, but also has unavoidable manufacturing and other errors, which were already mentioned in § 2.2.5.2 above. The errors of individual ASIs differ from each other, reason why each ASI needs to be cali- brated individually in a laboratory and its error published in a calibration report (small table) and furnished to the pilot (FAR 23.1323). The IAS indicated by two ASI’s in one cockpit may disagree with ± 4 kt (total of 8 kt) due to different instrument errors. The differences of instrument errors between ASIs in the same cockpit and in the fleet of airplanes of the same type for which a single AFM applies, and changes in instrument errors due to future maintenance replacements of ASIs, are the reasons that limiting and operational airspeeds cannot be furnished as IAS in such an AFM. The indicated airspeed IAS is not accurate enough to be of direct value to pilots. The IAS of two airplanes flying in formation are most probably not equal, while their CASs should be. 2.2.7. As noticed during reviews of manuals, many if not all AFMs consider the instrument er- ror to be zero, which is not in compliance with FAR 23. It makes the IAS less accurate. IAS is not really an airspeed of the airplane, but an airspeed comprising errors. A proper definition of Indicated Airspeed (IAS) is: IAS is the airspeed indicated on an airspeed indicator and is CAS including the pitot-static position and instrument errors 2.2.8. Ground Speed (GS). The flow of the airmass through the atmosphere, such as the wind, also has influence on navigation. The speed of the airplane relative to the ground, called the Ground Speed, is the TAS plus or minus a tail- or headwind component. Ground speed allows cal- culating the distance travelled in a period. Finally, the definition of Ground speed (GS) is: GS is the airspeed relative to the ground, and is the TAS corrected for the wind 2.2.9. Equivalent Airspeed (EAS) is still taught by Test Pilot Schools and universities, and was used by pilots before World War II, but the difference with Calibrated Airspeed is small and within acceptable tolerances for Part 23 airplanes. Refer to course book Pitot-Statics and the Standard Atmosphere in footnote 11 on page 3 for further explanation. 2.2.10. Further reading. Refer to the (free) book Pitot-Statics and the Standard Atmosphere in footnote 11 on page 3 for a complete course at MSc level on pitot-statics, airspeeds, altitudes, and the standard atmosphere. 2.2.11. The altimeter errors were not mentioned, but are also addressed in FAR 23. The calibra- tion is required in FAR § 23.1325(e). 2.3. Calibrated and Indicated Air Speeds in FAR and EASA CS (and equivalent) 2.3.1. Reference is made to FAR 23, but this review also applies to EASA Certification Specifica- tion CS- 23. FAR 23 "prescribes airworthiness standards for the issue of type certificates, and changes to those certificates, for airplanes in the normal, utility, acrobatic, and commuter cate- gories. Each person who applies under Part 21 for such a certificate or change must show compli- ance with the applicable requirements of this part". Hence, FAR 23 is intended to be used by airplane design engineers for designing airplanes Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 8 (including sizing the vertical tail); and for the certification of the airworthiness of the airplanes. Non-compliance with FAR 23 renders the type certificate and hence, the certificate of airworthi- ness of an individual airplane invalid. Below, a few relevant FAR paragraphs are described and explained that are needed during this review. 2.3.2. GAMA Specification is originally intended for Normal Category Airplanes, but it is also used for Commuter Class AFM. Therefore, several Regulatory paragraphs of FAR 23 (1-1-10 Edi- tion) for normal category (< 9 pax), commuter category (< 19 pax and MTOW < 19,000 lb), and SFAR No. 23 (> 10 occupants/Part 135), about airspeeds are partly copied below with some re- marks added. This chapter was originally written for an FAA certified airplane, which is the rea- son for references to FAR § 23. The review also applies to CS 23 paragraphs. 2.3.3. FAR § 23.1581(d) requires: "All Airplane Flight Manual operational airspeeds, unless oth- erwise specified, must be presented as indicated airspeeds". This requirement did not yet exist in the 1970 edition of FAR 23, and must have been included after the issue of GAMA Specification No. 1, which was regrettably not written with a high level of aeronautical expertise, as will be shown in this review below and in the Limited Review of GAMA Specification No.1 for Pilot's Op- erating Handbook12. It is an impossible requirement written and approved by incompetent peo- ple. Refer to § 2.4 below for a detailed explanation. 2.3.4. FAA Flight Test Guide AC 23-8C3 in Section 2, § 3 d specifies for commuter category air- planes: "(1) Takeoff Speeds. The following speed definitions are given in terms of calibrated air- speed”. The "following speed definitions" are those of: VEF, V1, VR, VLOF and V2. Not included are VS and VMC, although both are used to calculate VR and V2. Limiting speeds VS and VMC should therefore also be specified here as calibrated airspeeds, like in FAR § 23.51 and § 23.149. These operational airspeeds are determined and/or calculated following (experimental) flight tests, and usually presented as CAS for reasons described in the paragraphs above and in § 2.4 below. These do not need to be presented in IAS in an AFM. The AC 23-8C quote continues with: “The AFM presentations are required, by 23.1581(d), in indi- cated airspeed (lAS)", except for the "following" operational and limiting airspeeds, that were mentioned above. AFM presentations cannot be (accurate) in IAS in an AFM that applies to a se- ries of airplanes, and of which the instrument errors are assumed zero. This requirement must have been included following the issue of GAMA Specification No. 1 which, as will be shown in this review, is not written with competence at a high aeronautical level of knowledge. What a pilot must do is find the appropriate and needed operational and limiting airspeeds in CAS for a particular flight in the AFM data tables and/or graphs, and correct these to IAS by applying both the position error in the AFM and the instrument error found in the calibration report of the ASI (a small table) installed in the particular airplane during prefight and present these IAS values on the Takeoff and Landing Data (TOLD) card for use in the cockpit, one for each ASI. Presenting IAS in an AFM that is for a series of airplanes is intolerable and asking for fatal accidents, and is not in compliance with FAR 23 either. See further § 2.4 below. 2.3.5. Pt. 23, SFAR No. 23, § 5(b)(1) requires decision speed V1 to be in CAS. V1 is calculated using VS and VMCG, so these speeds must also be provided in CAS (FAR § 23.51 and § 23.149). 2.3.6. Pt. 23, SFAR No. 23, § 7 and FAR § 23.73 also require the landing approach speed VREF in CAS, because the source speeds VMC and VS are in CAS (FAR § 23.51 and § 23.149). 2.3.7. Pt. 23, SFAR No. 23, § 20 (f) determines that the performance information in the AFM must include: "Airspeeds, as indicated airspeeds, corresponding to those determined for takeoff in accordance with section 5(b)". Section 5(b) defines takeoff speeds V1 and VR in CAS, because VS and VMC are also determined in CAS (FAR § 23.51 and § 23.149). The instrument errors between airplanes differ, hence the takeoff speeds in IAS (as required here) will not be accurate in an AFM 12 Harry Horlings, AvioConsult, Limited Review of GAMA Specification No.1 for POH’s, https://www.avioconsult.com/down- loads/GAMA%20Specification%20No.1%20for%20Pilot's%20Operating%20Handbook,%20Limited%20Review.pdf Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 9 that applies to a series of airplanes of the same type. This is not in compliance with other para- graphs in FAR 23 either, such as § 23.51. 2.3.8. FAR § 23.51(a) requires rotation speed VR for normal category airplanes to be not less than 1.05 VMC or 1.1 VS1. As VMC and VS are determined in CAS, VR will also be in CAS (see also the Flight Test Guide quote in § 2.3.3 above). For commuter category airplanes (§ 23.51(c)), V1, VR, and V2 must be established/selected in terms of CAS as well. Hence, FAR § 23.51 specifies the operational takeoff speeds V1, VR, and V2 and stall speed VS to be presented as CAS in the AFM. FAR § 23.73 specifies the landing approach speed VREF as CAS, and FAR § 23.149 specifies both VMC and VMCG as CAS. Hence, these are the operational and limit- ing airspeeds that are "otherwise specified" (§ 2.3.3 above) and hence, should not be presented as indicated airspeeds in an AFM, the reason being that these speeds are critical to flight safety and need to be quite accurate and reliable. As mentioned in § 2.3.4 above, the pilot must calcu- late the IAS values of the operational and limiting speeds and present these on a Takeoff and Landing Data card for use in the cockpit, and relate with the airspeed indicated on the ASI. 2.3.9. FAR § 23.1323(a) and Pt. 23, SFAR No. 23, § 13(a) require: "Each airspeed indicating in- strument must be calibrated to indicate true airspeed (at sea level with a standard atmosphere) with a minimum practicable instrument calibration error when the corresponding pitot and static pressures are applied". Each ASI is calibrated in a laboratory to determine its instrument error, being the error between the air pressures at the entrance ports (PT and Pa) and the airspeed indicated by the pointer on the dial of the ASI. The IAS + the instrument error is also called Vic (§ 2.2.5.3). There is no requirement for ASI calibration at higher altitudes, only for a range of speeds at sea level, because the reference airspeed and temperature used in the ASI are standard atmospheric sea level pressure and density (Figure 2). At sea level, TAS = CAS. 2.3.10. FAR § 23.1323 (b) requires: "Each airspeed system must be calibrated in flight to deter- mine the system error. The system error, including position error, but excluding the airspeed indi- cator instrument calibration error, may not exceed three percent of the calibrated airspeed or five knots, whichever is greater, throughout the following speed ranges: …" A similar requirement in Pt. 23, SFAR No. 23, § 13A: "The airspeed indicating system must be cal- ibrated to determine the system error, i.e., the relation between IAS and CAS, in flight and during the accelerate takeoff ground run", and in § 13(d): "information showing the relationship be- tween IAS and CAS must be shown in the Airplane Flight Manual". The system error is the position error plus the lag error (Figure 2 above), but excluding the in- strument error. The lag error is often neglected because it has effect only during pressure changes, which do not occur during steady straight flight. Hence, the relationship between IAS and CAS is the sum of the instrument error of the ASI and the position error of the pitot-static system: CAS = IAS + instrument error + position error. The instrument error cannot be presented in an AFM for a series of airplanes of the same type, as explained above, only the position error must be provided in a chart or table. The instrument er- ror should be mentioned though in the AFM, certainly in the legend of the position error chart, because the pilot must read the airspeed instrument correction from an instrument error correc- tion table and add this to the IAS to calculate the instrument corrected airspeed (Vic) which is then used to enter the position error chart to read the position error or CAS. An IAS to Vic con- version table is to be made and be available for each individual ASI (for each serial number). 2.3.11. So, FAR § 23.1323 requires both the pitot-static system and the airspeed indicator in- strument to be calibrated separately. The calibration data of both must be made available to the pilot to be able to calculate the CAS from the IAS during flight, and to calculate pre-flight deter- mined performance data and takeoff speeds from CAS in the AFM to IAS for use in the cockpit (on the Take Off and Landing Data (TOLD) card). The GAMA Specification No. 1 seems not to mention the instrument calibration error, on the contrary, GAMA assumes and recommends zero instrument error and therefore does not comply with FAR 23. It should not have been ap- proved by the aviation authority. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 10 2.3.12. FAR 23.1581. "An Airplane Flight Manual must be furnished with each airplane, and it must contain the following: (1) Information required by §§23.1583 through 23.1589. (2) Other information that is necessary for safe operation because of design, operating, or han- dling characteristics." §§ 23.1583 and 23.1587 are copied in the next paragraph. Not only minimum control speed VMC must be furnished as number, but also other information necessary for safe operation after en- gine failure. VMC and its associated conditions will be explained in § 2.5 below. 2.3.13. FAR 23.1583 requires that "the AFM must contain operating limitations", including: "(1) Information necessary for the marking of the airspeed limits on the indicator as required in §23.1545, and the significance of each of those limits and of the color coding used on the indica- tor. (2) The speeds VMO, VO, VLE, and VLO, if established, and their significance". Hence, the airspeed limits that require marking on the indicator must be furnished in the AFM. The limiting airspeeds are established in CAS. The marks must be located at the corresponding indicated airspeeds, meaning at CAS minus the position error of the pitot-static system and mi- nus the instrument error of the to be marked airspeed indicator. If the instrument error is con- sidered zero in the POH/AFM, then the markings might be on a wrong location on the indicator. The error can be up to ± 4 kt, a range of 8 knots. In addition to the markings, the significance of the speeds in (2) must be contained in the AFM. 2.3.14. In FAR § 23.1587(d): "In addition to paragraph (a) of this section, for commuter category airplanes, the following information must be furnished— (10): The relationship between IAS and CAS determined in accordance with §23.1323 (b) and (c)"; (is an error, must be (a) and (b)). The relationship between IAS and CAS is the sum of the position error (≤ 5 kt) and the instrument error (≤ 4 kt), i.e. is between 0 and 9 kt depending on the airspeed, and can be 3 kt higher due to the approved friction error when the airspeed decreases or increases. This FAR paragraph requires both the position error and the instrument error to be furnished. The position error is usually published in a chart in the AFM, but the instrument error seems for- gotten, while it can be larger than the position error. Not furnishing instrument errors, or assum- ing instrument errors to be zero is not in compliance with this FAR paragraph. 2.3.15. Summary IAS and CAS in FAR. The use of IAS and CAS in Regulations is confusing and, given the GAMA Specification No. 1, is not understood either, is even misinterpreted. The im- pression is that several paragraphs were changed to match GAMA Specification No.1, while other paragraphs are not, causing inconsistencies (§ 2.3.3). The GAMA Specification No. 1 is in- deed mentioned in the FAA Flight Test Guide (page 163 and more). The consequences of chang- ing airspeeds from CAS to IAS in POHs/AFMs might not have been obvious to the rule makers, because of lack of proper high-level knowledge of pitot-static systems and its errors. 2.3.16. The (improper) FAR requirement for the use of IAS in AFM can only be met if, besides the position error, also the instrument errors of each individual ASI in all airplanes of the same type, for which the AFM applies, are known to the AFM-writer, including the errors of a second or third (alternate) ASI in the same cockpit. This would lead to a large data table, the use of which would be prone to errors. Requiring to present IASs in an AFM requires a separate AFM for each individual ASI (due to its instrument errors), and not just one AFM for a series of air- planes of the same type. This is expensive, and not acceptable for controlling the manuals. A maintenance replacement of a defective ASI would lead to a change in many if not all IASs pub- lished in an AFM. Changing limiting or operational airspeeds in the FAA approved part of an AFM requires approval of the FAA and printing new manuals, which takes quite some time during which the airplane is grounded, unless the instrument error of the new ASI is the same as of the replaced ASI. In addition to the amendment of the AFM of the specific tail number, the required red radial line indicating VMC on the ASI (FAR § 23.1545(b)(6)), or for airplanes >6000 lb and turbine engine- powered airplanes the placard in the cockpit (FAR § 23.1563(c)) with airspeed limitations also Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 11 needs to be amended and/or replaced. If the instrument error is considered zero, then the AFM will not include the instrument error with the consequence that the markings on the new ASI and/or placard will not be at the correct position (§ 2.3.13, FAR § 23.1583). Safety is at stake. This cannot be the intention of these FAR requirements; it is obviously unworkable, and must be in error (or is misunderstood). An ASI must be accompanied by an instrument correction table for a range of airspeeds on the instrument panel, for the pilot to be able to calculate the indi- cated airspeed, and the markings must be at the right place. When the author of this review started flying Part 23 airplanes in the early seventies, such a table could still be found on the in- strument panel. It seems that many manufacturers avoid the use of the instrument error by prescribing a zero- knot instrument error in their AFM, unaware of the consequences for flight safety. The relation- ship between CAS and IAS is then only the pitot-static position error, but this is not in compliance with FAR 23, and leads to inaccurate indication of limiting and operational speeds, and to fatal accidents. 2.4. Calibrated and Indicated Air Speeds in an AFM 2.4.1. The takeoff, stall, minimum control, cruise and landing approach speeds, and the han- dling qualities of the airplane were determined during experimental flight tests with a calibrated airspeed measuring system, and were reported as CAS for a given gross weight (mass). These, for flight operations important speeds are usually also published as CAS in an AFM because then they are valid for all airplanes of the same type, for which the AFM applies. As also mentioned above, another reason for publishing airspeeds as CAS is that the AFM-writer does not know the instrument error of each individual ASI installed in any production airplane (at any one time, now or in the future). The position error of the pitot-static system must be published for a range of airspeeds in a chart in the AFM. An airspeed instrument error correction table should be availa- ble showing the airspeed correction for each individual installed ASI, except for a few categories of airplanes, unless the errors are compensated for in a computerized air data system (§ 2.2.5.5 above). The airspeed instrument correction table should be mentioned in the AFM, like all re- quired placards are. With this table, and with the position error chart in the AFM, the pilot can determine the Indicated Airspeed to maintain a desired Calibrated Airspeed (that is published in the AFM as limitation, procedural, or performance speed) and write these on the Take Off and Landing Data card. 2.4.2. GAMA Specification No. 1 requires airspeeds to be published as IAS, because "the pilot exclusively works with IAS" (Preface). The pilot who wrote this, or who approved this on behalf of all GAMA members is not a competent pilot, and probably never studied pitot-statics at a higher level than PPL level. It is also incomprehensible that GAMA members approved this; none of them obviously consulted a graduate of one of the test pilot schools or an aeronautical engineer. They might not even employ one, which proves unprofessionalism, leading to the question whether their airplanes are well developed and flight-tested. In addition to the quote in the Preface of GAMA Specification No. 1, § 2.3 requires "airspeed limi- tations and the operational significance of such limitations shall be provided as CAS and IAS (as- suming zero instrument error)". This might cause confusion, and certainly also errors because the instrument errors of all individual airspeed indicators are and cannot be included in an AFM that applies to a series of airplanes of the same type, only the position error in the relationship be- tween IAS and CAS can (§ 2.3.10 above). This requirement is not in compliance with FAR 23. A recommended instrument error of zero knot might lead to controllability problems, while the pilot believes to be safe when reading the ASI, as an example will show. 2.4.3. An example: The minimum control speed VMC, determined during experimental flight- tests, is 66 KCAS. With a position error CAS to IAS of −2 kt, and an instrument error of +4 kt, the indicated VMC is 66 – 2 + 4 = 68 KIAS. In an AFM that publishes indicated airspeeds with a zero instrument error, as GAMA recommends, the published VMC of 66 KCAS is indicated on the ASI as 66 – 2 = 64 KIAS. When maintaining 64 KIAS, the red-lined or placarded VMCA, the pilot believes to Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 12 be safe, but this airspeed is 4 kt, the magnitude of the instrument error, below the published VMC (68 KIAS), and he will lose control when an engine fails, the other engine is set at maximum thrust, and the small favourable bank angle is not maintained. The takeoff speeds (in IAS), if cal- culated using VMC as IAS with zero instrument error, will also be too low. If the VMC marking on the ASI of normal category Part 23 airplanes is positioned using both the position and the instru- ment errors, then the pilot will notice when his airspeed is below the published VMC. The increase of VMC with the wings level is not included (§ 2.5.10). CAS and both errors are re- quired to provide safe VMC and other limiting and operational speeds to the pilot. 2.4.4. Readers, like the writers of the GAMA Specification No. 1 and the reviewers of the FAA, might believe 1, 2 or even 4 kt is not that big of an (instrument) error, so why all the fuzz. But it is not about the few knots, it’s all about physics, about the forces and moments generated by the freestream air at the calibrated airspeed around the wings and the aerodynamic control surfaces that produce the lift and the control forces which are required to maintain the equilibrium of forces and moments, i.e. to maintain control of the airplane. The aerodynamic forces are propor- tional to the square of the airspeed (V2), as shown in the lift equation: Lift = CL ½ρV2 S. A few knots difference at a higher speed has a large influence on the generated control forces, which increase with increasing airspeed (V2). A rudder ratio changer in large airplanes prevents over- loading the vertical fin, by reducing the rudder deflection per degree of rudder pedal travel with an inverse quadratic function of the increasing airspeed rather than with a few knots. 2.4.5. Looking at his ASI, the pilot might consider to be at the correct speed, but his controls do not produce the control forces as expected or he might not have the control travel available that he needs; control might be lost. FAR 23 requires airspeeds to be provided accurately; rules were made many years ago with competence and should not be amended or neglected by igno- rance, because physics has no mercy. Pilots have the right to be made aware of the errors in the pitot-static systems for them to be able to apply the correct speed corrections and hence, apply the correct and safe operational and limiting airspeeds, which were determined in CAS, to conduct a flight and return home safely. Pilots cannot be allowed to "exclusively work with IAS". If they do, their airplane is not air- worthy as required by FAR 23. Pilots must work with CAS in graphs and tables in a type generic AFM, and must add the position error in the AFM and the instrument error of the particular ASI in the airplane to the CAS to obtain IAS to be able to relate to, to work with, airspeed indications and markings on the ASI in that specific airplane (tail number). 2.4.6. In GAMA Specification No. 1 many more statements are found that are not in agreement with FAR 23 and FAA Flight Test Guide. The writers and/or advisors of the Specification obviously had a disappointing low-level understanding of airplane speeds, performance, and control, and of FAR 23. An AFM prepared with their Specification No. 1 did not contribute to preventing the many fatal accidents referred to in § 1.1 above. GAMA made a huge mistake by not hiring aero- nautical expertise at MSc or test pilot school level. It is also incomprehensible that the FAA ap- proved GAMA Specification No. 1 and the many different AFMs that were prepared using the Specification. 2.4.7. An AFM is designated by number in the Type Certificate Data Sheet of the airplane, and is mandatory for the airplane to be operated airworthy. Many accidents occurred and were in- vestigated by TSBs around the globe, but obviously none of these boards reported errors in the AFM and recommended or mandated improvements during the past 50 years. Aviation is drifting into failure due to incompetence of key-personnel that the public relies on. 2.5. Minimum Control Speed VMC or VMCA 2.5.1. When an engine of a multi-engine airplane fails or is inoperative, the pilot needs to counteract the asymmetrical thrust yawing and rolling forces and moments using the rudder and ailerons continuously. Therefore, a flight with asymmetrical thrust is not a coordinated flight. The forces and moments generated by the aerodynamic controls rudder and aileron are propor- tional to the square of the airspeed (V2). So, whatever the attitude or configuration of the Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 13 airplane, there always is an airspeed below which the asymmetrical thrust, gravity induced forces, and other forces and moments can no longer be counteracted with rudder and ailerons, and an equilibrium of forces and moments can no longer be maintained. This airspeed is called the minimum control speed. FAR 23 defines minimum control speed as VMC for the takeoff configuration which is to be pub- lished in the AFM. Other publications also use VMCA, for VMC "in the Air, or Airborne". Both refer to the same speed. This review uses both abbreviations separately or combined as VMC(A), but in ad- dition also "actual VMCA", which is the VMC when the configuration, flap setting, bank angle, etc. are not as prescribed in FAR 23.149 for the takeoff configuration, and a higher airspeed is re- quired to maintain the equilibrium of forces and moments for actual circumstances, such as a larger bank angle, a non-feathered propeller, or other asymmetrical drag. A minimum control speed applies always in-flight in anticipation of, and following an engine failure, not only during takeoff. The actual VMCA increases above the published VMC with bank angle, i.e. during turns, as will be explained below. 2.5.2. During reviewing the GAMA Specification No. 1, several AFMs, and many investigation reports of accidents after engine failure, it was noticed that the pilots and the investigators were not aware of the real value of VMC, and of the associated conditions for VMC to be valid. Therefore below, in addition to the papers presented on the website of AvioConsult, a few highlights of VMC are explained using FAR 23, the FAA Flight Test Guide AC 23-8C, and courses of a test pilot school, one of which is for the prediction of VMC prior to conducting VMC testing. Copies of the applicable Regulatory paragraphs, Flight Test Guide and course manuals are brought together in one Background Info pdf file13 for the reader to verify what is written below. 2.5.3. VMC is defined in FAR § 23.149(a) (and equivalent) as follows: "VMC is the calibrated air- speed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees". 2.5.4. This definition, intended for the design and certification of airplanes, is often inappropri- ately copied into Airplane Flight Manuals (AFM) but is usually misunderstood by pilots and acci- dent investigators. To improve the understanding of VMC, this paragraph briefly explains the siz- ing of the vertical tail, the effect of bank angle on VMC, and the flight test techniques used to de- termine VMC. Readers will be become familiar with the real value of the VMC that is published in the AFM of multi-engine airplanes and with the conditions for which the published VMC is valid, which is of vital importance for preventing engine failure related accidents and for getting home safely after an engine failure. Accident Investigations will also improve. 2.5.5. Limitations Due To the Size of the Vertical Tail. In Figure 4 below, the most important forces and moments are shown that act on a multi-engine airplane during steady straight flight when engine #1 is inoperative and the wings are kept level. As for any physical body, an airplane is in equilibrium if both the sum of the forces and the sum of the moments that act on the air- plane are zero. To counteract the asymmetrical thrust yawing moment, the deflected rudder generates a side force that causes a rudder yawing moment opposite of the thrust yawing mo- ment. The rudder side force however, also causes an acceleration to the dead engine side which results in a sideslip angle and in an opposite side force due to sideslip. The sideward acceleration continues and the resulting side force due to sideslip increases, until the sum of the side forces is zero. The aerodynamic rudder side force is proportional to the (square of the) airspeed (≡ V2). The lowest airspeed at which straight flight can just be maintained while either the rudder or the ailerons are maximum deflected and the asymmetrical thrust is maximum is called VMC, in this case VMC with the wings level. A sideslip however, also causes drag which reduces the remaining climb performance significantly and should therefore be kept to a minimum, especially during initial climb when an engine is inoperative, but also during cruise for maximum range. To 13 AvioConsult, Background information for the definition, theory, flight test and use of VMC, https://www.aviocon- sult.com/downloads/Background VMC(A) Regulations and Flight Test.pdf Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 14 achieve minimum sideslip hence drag, a small bank angle can be used (during straight flight), as explained next. 2.5.6. For explaining turns, pilots use the centripetal force, being a horizontal component of the lift of the wings in the earth axis coordinate system. However, following an engine failure, the required counteracting rudder side force affects the magnitude of the centripetal force. In addition, the increased drag due to sideslip might affect the remaining wing lift. Hence, the cen- tripetal force can only be used for coordinated flight, when all engines are operating and the controls are near center. This cannot be the case after engine failure, therefore airplane design engineers and test pilots use the body axis coordinate system in which a component of the weight, rather than the wing lift, provides the side force, because gravity (Weight) always acts on an airplane, whatever the bank angle or attitude. The lift of the wings acts in the direction of the z-body axis and hence, has no side component in the body-axis system, but the Weight does. When banking, a component of the weight (W) results in a side force due to bank angle (W⋅sin ϕ in Figure 5), that replaces the side force due to sideslip that was a consequence of the rudder deflection (Figure 4). The small bank angle decreases the sideslip angle of the airplane to a mini- mum, decreasing the total drag and hence, increases the (climb) performance. Side force W⋅sin ϕ acts in the center of gravity (moment arm is zero) and therefore does not cause a yaw- ing moment. As the rudder side force, generated by the vertical tail with rudder, no longer must act against the side force due to sideslip as well (see Figure 5), but only against the thrust yawing moment, the rudder deflection can be smaller, or the vertical tail can be designed smaller to save manufacturing cost and weight, and still comply with the Regulations. FAR 23.149 allows the engineer designing the vertical tail to use a bank angle of maximum 5° (away from the inop- erative engine), while maintaining straight flight, for sizing the vertical tail with rudder. In any Figure 4. Lateral-Directional forces and moments in body axis coordinate system, wings level. OEI, straight flight. Forces are not to scale. Figure 5. Lateral-Directional forces and mo- ments in body axis coordinate system, bank angle 5° into good engine. OEI, steady straight flight. Forces are not to scale. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 15 case, when maintaining a small bank angle into the good engine, VMC is lower than with the wings level, and the sideslip angle, hence drag, is minimal. 2.5.7. A smaller vertical tail requires a higher airspeed to counteract the same maximum thrust yawing moment; VMC will be higher. FAR 23.149(b) however, does not allow the vertical tail to be made so small that VMC for takeoff, i.e. during straight flight with max. 5° of bank, exceeds 1.2 times the stall speed (VS). Hence, the vertical tail is made just large enough to be able to main- tain straight flight at airspeed VMC while the thrust of the opposite engine is at the maximum takeoff setting, the rudder is maximal deflected and a small bank angle is being maintained as opted during sizing the vertical tail, which is usually between 3° and 5° away from the inopera- tive engine. Refer to Airplane Design Part VII, Dr. Jan Roskam of Kansas University (footnote 10 on page 3). The vertical tail with rudder is only sized large enough for maintaining straight flight at VMC at maximum asymmetrical thrust and with 5° bank into the good engine In-flight, the pilot controls the bank angle (if control is not lost) and hence, determines the mag- nitude of side force W⋅sin ϕ; the pilot controls the actual VMCA with bank angle and thrust. There- fore, the effect of bank angle (ϕ) and weight on VMCA is worth reviewing in greater detail. 2.5.8. Effect of Bank Angle and Weight on VMCA. When, during the design phase of the air- plane, the size of the vertical tail with rudder is either known or assumed, graphs can be calcu- lated using lateral-directional equations of motion with the stability derivatives of the airplane to show the effect of bank angle and weight on VMCA while the thrust is maximum asymmetrical, refer to paper The Effect of Bank Angle and Weight on VMCA14. The resulting graphs presented in Figure 6 and Figure 7 below are calculated in this paper using stability derivative data of a sample 4-engine turbojet airplane. Such calculations are usually also done to predict VMC prior to con- ducting VMC flight-testing with prototype airplanes. Data of a twin-engine airplane were not avail- able; the shape of the graphs is approximately similar for all multi-engine airplane types, though. 2.5.9. Figure 6 shows that the sideslip angle β is near zero, i.e. the drag is minimal, when the bank angle is 3° away from the inoperative engine for this swept wing airplane. The correspond- ing standardized VMC (with maximum rudder deflection) that is published in the AFM is 95 kt. The small bank angle should be, and sometimes is included as an associated condition in the legend of one engine operating performance diagrams for the presented data to be valid. 2.5.10. As already mentioned above, bank angle not only has great effect on sideslip, hence on drag and performance, but bank angle (ϕ) and Weight (W) both have also great influence on the actual VMCA of the airplane, being the VMCA which the pilot will experience in-flight, through side force W⋅sin ϕ, as is illustrated in Figure 5. Figure 6 and Figure 7 show that the actual VMCA of this sample airplane increases from the published 95 kt to 119 kt if the wings are only kept level. For small twins this increase will be ≈ 6 kt. In addition, keeping the wings level or banking to either side results in a large sideslip. Sideslip is a result, not a cause, and increases the drag and hence, reduces the climb performance or leaves no positive climb performance at all (in small twin en- gine airplanes). 2.5.11. Another important observation of Figure 6 should be that when banking more than 6° into the good engine, the rudder deflection should be reduced and reversed to maintain the bal- ance of forces and moments, i.e. to maintain control. Sometimes, test pilots increase the bank angle to the point where the rudder deflection is zero, the third test point in Figure 6. At that point, the sideslip angle is near 14°, the angle at which the fin with deflected rudder is very close to a stall, and hence, the drag very large. This might be the reason that FAR 23.149 allows "not more than 5° ". Figure 6 proves that it is a myth that banking into the good engine(s) is favoura- ble to the safety margin above VMCA. VMCA increases considerable with banking to either side to values above VMC for straight flight. 14 AvioConsult - Harry Horlings, The Effect of Bank Angle and Weight on VMCA, https://www.avioconsult.com/downloads/Effect of Bank Angle and Weight on Vmca.pdf Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 16 2.5.12. Figure 7 shows the effect of bank angle and weight on VMC. VMC when maintaining a 3° bank into the good engine decreases with increasing weight. When the wings are kept level, weight has no influence on VMC; the side force due to weight (W∙sin ϕ = 0). This graphs also shows that VMC with a small bank angle away from the failed engine is highest at low weight, which is the worst-case weight for VMC during straight flight while maintaining a small bank an- gle, which is the reason that low weight is used to determine VMC (for straight flight − FAR 23.149). VMC increases with weight when the bank angle into the dead engine increases. At high weight (takeoff), VMC increases considerable while banking. This increase is not included in Fig- ure 6. 2.5.13. It will be clear that the requirement for maintaining straight flight while also maintaining a small bank angle away from the inoperative engine must be made well known to the pilots of multi-engine airplanes to avoid the loss of control when maximum thrust is needed on the oper- ating engine. The saved weight and manufacturing cost of a smaller vertical tail (hardware) needs to be replaced by a quite 'heavy' associated condition / warning in the AFM (software) for only maintaining straight flight and a small bank angle while an engine is inoperative and the asymmetrical power setting is, or is increased to maximum. This prerequisite for maintaining control after engine failure is regrettably not presented anymore in most AFMs, in multi-engine rating coursebooks, and in investigator training manuals; it is forgotten knowledge during the past 50 years. 2.5.14. Flight-Testing To Determine VMCA. During the flight-test to determine VMCA in accord- ance with the FAA Flight Test Guide3, the airplane is in the same configuration as was used to de- sign the vertical tail, of which the most important factors are the lowest weight possible (small- est side force W⋅sin ϕ), an aft center of gravity (smallest rudder moment arm), maximum power setting that the pilot can set from the cockpit on the operating (critical) engine (maximum thrust yawing moment) and a feathered propeller, if applicable and automatic (lowest propeller drag). This configuration results in the 'worst-case' VMC (for straight flight). Two types of VMC are deter- mined, first the static VMC and then the dynamic VMC. Figure 7. Effect of bank angle and weight on VMC(A). NOTE. C-130 pilots know this figure, because it is like the Weight and Bank Angle figure in the C‑130 Performance Manual SMP-777. Figure 6. Effect of bank angle on VMCA, and on rudder, aileron, and sideslip angles. Equilibrium flight at maximum thrust, for a sample airplane. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 17 2.5.15. The static VMC is the VMC for maintaining straight flight while an engine is inoperative. The airspeed is slowly reduced (keeping the wings level) until the heading can no longer be main- tained using maximum rudder or aileron deflection, or up to the FAR defined maximum control force limits (150 lbf for rudder pedal, 25 lbf for roll control). This first data point is the wings- level VMC (Figure 6 - top). Then, while applying the same bank angle that was used to design the vertical tail (3° to 5° away from the inoperative engine), the speed is (and can be) further re- duced until again the heading can no longer be maintained. This speed is the static VMC of the airplane and is usually between 6 (small twin) and 25 knots (B707) lower than the wings-level VMCA. This VMC is obviously only valid during straight flight when the small favorable bank angle is being maintained. When the bank angle for zero rudder (Figure 6 – bottom) is attained, VMC is a bit lower, but the sideslip (drag) increases. VMC for other bank angles is never determined be- cause of the many variables that affect the balance of forces and moments and therewith VMC. The VMC prediction method was used to calculate the actual airspeed for every bank angle be- tween − 15° and + 15° for which either the rudder or the aileron deflection is maximum, or the sideslip angle is 14°, being the stall angle of attack of the fin with deflected rudder (large cam- ber), as shown in Figure 6 The VMC data on the left edge (lowest weight) in Figure 7 coincides with the VMC data in Figure 6. A higher weight affects the actual VMC. With zero bank angle, weight has no effect (side force W∙sin 0° = 0). 2.5.16. The dynamic VMC is important for regaining control immediately following the sudden failure of an engine during the resulting dynamics, and is determined by cutting the fuel flow to the critical engine at several speeds down to the speed at which either the heading change is maximum 20°, the bank angle does not exceed 45° and no dangerous attitudes occur. 2.5.17. The static VMC is usually higher than the dynamic VMC. The highest of static and dynamic VMC will be published as the VMC of the airplane in the AFM, but a VMC applies during the whole remainder of the flight, including the final turn for landing. Flight testing (and demo) of VMC is not without danger; therefore, the test data are acquired at a safe altitude and extrapolated to sea level. 2.5.18. FAR 23.149(b) defines VMC for the takeoff configuration, for straight flight (climb out) at maximum thrust, and to be always as low as the red (radial) line on the ASI or as placarded. But a VMC applies during the whole flight when an engine is inoperative, which might be the reason that VMCA (VMC in the Air) is used in many publications, including in the subject AFM. VMCA is de- fined in POH § 0.6, while in the manual also the undefined VMC is used. So, it is recommended to add the FAR 23 VMC definition for the takeoff configuration and straight flight, modified for pilots, and explain in the VMCA definition that an actual VMCA always applies in anticipation of, and fol- lowing an engine failure during the remainder of the flight, that VMCA increases during turns to an undetermined actual value, and that VMCA can be ‘managed’ with the throttle of the operating engine and with the bank angle. 2.5.19. Definition Of VMC in an AFM. FAR 23 prescribes the airworthiness standards to be used by airplane design engineers (§ 2.3.1 above), including requirements for the case one of the en- gines is inoperative, including the provision of the minimum control speed VMC. The VMC defini- tion in an AFM is often copied out of Federal Aviation Regulation (FAR 23.149) or equivalent, as quoted in § 2.5.3 above. Once the airplane is in operational use, for which the AFM applies, pi- lots should not keep the wings level to within 5° of bank, left or right, as the definition suggests. On the contrary, in order to ensure that control of their airplane after engine failure can be maintained when maximum thrust is set, and that the remaining climb performance is maximum achievable while one engine is inoperative, pilots need to maintain straight flight and the same small bank angle that was used to design the vertical tail and that was also used to determine the AFM-published VMC during flight testing, which is usually between 3° and 5° away from the inoperative engine, as was illustrated in Figure 6 and Figure 7 above. A larger bank angle, or a bank angle into the inoperative engine, will disturb the balance of side forces and yawing mo- ments and will result in lateral accelerations and yawing moments (and sideslip) that cannot guaranteed be balanced using the aerodynamic controls, simply because the vertical tail with Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 18 rudder (and the ailerons) were not sized large enough to do so when the thrust is maximum. The words suddenly made inoperative and critical engine in the VMC definition in an AFM do not make sense at all for, and are misleading to, pilots; a VMCA applies during the entire flight, prior to and following the failure of any engine, not only the critical engine, and during climb, cruise and ap- proach or go-around when any of the engines already failed during takeoff. The above quoted FAR definition of VMC is deficient for use in an AFM. 2.5.20. The actual VMCA that a pilot will experience in-flight will be affected by any change of lat- eral or directional forces and moments, for instance by an accidently deployed thrust reverser or cowling, an opened cargo hatch, a non-feathering propeller, a camera mounted on a wingtip, un- balanced wing fuel, or a bad functioning throttle friction and, last but not least, yet often occur- ring, intentional or uncontrolled banking at too low a speed and too high an asymmetrical thrust level (to quickly return to the runway for landing). 2.5.21. The actual VMCA is in fact and in general the lowest airspeed which can be obtained with full directional or lateral control deflection and should be a factor of concern when the asymmet- rical thrust is or is increased to maximum (during a turn). The one engine inoperative climb performance is only maximal if a small bank angle is being maintained away from the inoperative engine; the bank angle for minimum sideslip can be less than 5° when the airspeed increases. The manufacturer should include this bank angle in the leg- end of the performance graphs of the AFM. 2.5.22. In the new FAR § 23.2135 (c) the VMC definition is: "VMC is the calibrated airspeed at which, following the sudden critical loss of thrust, it is possible to maintain control of the air- plane. For multiengine airplanes, the applicant must determine VMC, if applicable, for the most critical configurations used in takeoff and landing operations". After reading the explanation of VMC above, readers will agree that this definition is even worse than the old one (§ 2.5.3 above). VMC does not only apply during takeoff and landing operations, as accident statistics prove. VMC is determined for recovery and thereafter maintaining straight flight only, while also maintaining a specific bank angle (FAA Flight Test Guide AC 23-8C3). The rule makers were obviously still not aware of the forces and moments acting on an engine-out airplane, including the role of the 5° bank for small twins, as described above. It is now entirely up to the manufacturer to provide pilots with a definition that explains VMC and/or VMCA so excellent and unambiguous, that acci- dents after engine failure will never ever occur anymore. This review proves that manufacturers are not ready to do so. Supervision with higher level knowledge is still required. 2.5.23. Takeoff Speeds. The AFM-published VMC is one of the factors used for calculating the takeoff speeds, including the rotation speed VR and the takeoff safety speed V2. Since the pub- lished VMC is valid only while maintaining a small bank angle (3° to 5° away from the inoperative engine at the option of the manufacturer), both calculated takeoff speeds are also valid only while maintaining this bank angle, unless the 6 – 25 kt higher VMC for wings level (depending on the type of airplane), which is also determined during flight-testing, is being used. Manufacturers regrettably never include this higher wings-level VMC in their AFM, which could be the cause of many occurrences of Loss of Control just after liftoff. They don’t mention the increased sideslip hence drag, i.e. the reduced or negative Rate of Climb, either. 2.5.24. The VMCA data presented in Figure 6 and Figure 7 above apply for maximum asymmet- rical thrust. The actual VMCA decreases when reducing the asymmetrical thrust a little. This de- crease can be temporarily used by pilots to conduct a turn, following a straight climb to a safe altitude. This asymmetrical thrust reduction reduces the thrust yawing moment and therewith the required counteracting rudder deflection; the actual VMCA is lower. During turns, the sideslip increases though, and therewith the Rate of Climb. Some altitude might have to be sacrificed during turns, but control will be maintained. Engine-out flight is never a coordinated flight. Pilots need to be made aware and reminded of the significance of VMCA for engine-out flight in the AFM, as FAR 23.1583(a)(1) requires, not only of VMC for takeoff (§ 2.2.10 above). Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 19 2.5.25. Examples of controlling VMC(A) and of the significance of VMC(A) are included in the follow- ing abbreviated accident reports: The distribution of engine thrust for keeping the actual VMCA under control, and for allow- ing safe turns, when one or more engines are inoperative, was applied by a competent Boeing 707 flight crew after both engines #3 and #4 separated off the right wing above the French Alps (31 March 1992). During the turns for the approach, the copilot reduced the thrust of outboard engine #1 a bit and increased the thrust of inboard engine #2, thus re- ducing the sum of the asymmetrical thrust yawing moments while maintaining the same total thrust level. He in fact decreased the actual VMCA. He also recommended a minimum speed of 200 kt to the captain, who was the pilot-flying, and selected flaps one to unlock the outboard ailerons, therewith increasing the lateral control power. They landed safely on Airbase Istres − Le Tubé in France. Knowledge of forces and moments saved lives. Well done! Not all pilots think of managing forces and moments. Six months later, on 21 Dec. 1992 a Boeing 747 freighter also lost the two right engines #3 and #4 shortly after takeoff from Amsterdam Airport. Despite the damaged leading edge of the right wing, the airplane remained controllable and completed nearly two full descend- ing turns at less than maximum thrust on engines #1 and #2. When, during a right-hand turn to position for the approach, the thrust on both left-hand engines was increased to maximum, control was lost and the airplane went down in a suburb of the city. The asym- metrical thrust yawing moment had increased above the level that could be counteracted by the aerodynamic controls. The pilots were regrettably never made aware of the effect of bank angle and thrust on the actual VMCA of their airplane. The investigators of the acci- dent interviewed the Boeing 707 pilots, but did regrettably not conclude the increase of VMCA due to the inappropriate increase of thrust during the turn as cause of the accident. 2.5.26. Conclusion of the above is that VMC(A) varies with bank angle and thrust level. Manufac- turers are regrettably not required to publish the bank angle that was used to determine VMC, neither in the VMC definition, nor with VMC data in the AFM, while some manufacturers do publish the bank angle for minimum drag/maximum performance in the legend of OEI performance charts (Piper in the PA-44 POH, and Lockheed in C-130 manuals). The AFM should remind pilots with: 'Published VMC(A) is valid for straight flight only while maintaining a 5° bank angle into the good engine when the asymmetrical thrust is maximum. VMC(A) increases during turns', and: 'The pilot controls the actual VMC(A) with bank angle and (asymmetrical) level of thrust’. 2.5.27. To prevent accidents after engine failure, the manufacturer should describe how the published VMC(A) is determined, when this VMC(A) is valid, and elaborate on the variation of VMC(A) with bank angle, thrust, and other effects. An improved VMC(A) definition for pilots could be: 'Minimum Control speed VMC(A) is the lowest airspeed which can be obtained during steady straight flight while maintaining 5° bank towards the good engine, with full rudder and/or aileron control inputs when one engine fails or is inoperative, and the opposite engine is set at maximum thrust. The actual VMC(A) increases while banking to either side and with the thrust level of the good engine and hence, is controlled by the pilot'. 2.5.28. Pilots receive their multi-engine rating in Part 23 airplanes, and take this experience with them during their whole career in Part 23 and Part 25 airplanes. Wrong learned is wrong applied. Even Boeings 747 crashed after engine(s) separation because the pilots were not made aware of the increase of VMC(A) to a much higher actual VMC(A) while banking at maximum asym- metrical thrust. ICAO would call this a Systemic Error. GAMA Specification No. 1 must therefore provide adequate guidance on engine-out flight to prevent future Systemic Errors as well. 2.5.29. The actual VMCA depends on many factors, the worst cases of which are used during flight-testing. Actual VMCA can also be lower than the AFM-published VMCA, for instance due to a Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 20 forward cg. The paper Airplane Control and Analysis of Accidents after Engine Failure15, explains almost all about VMCA, and analyses a few accidents after engine failure. So far, the airspeed theory. In the next chapters, the Beech 200 POH will be reviewed. 2.6. Copies of the applicable regulations, flight test guide and course books are compiled in one Back- ground Info pdf file16 for the reader to quickly and easily verify the above. 3. Review of EASA Approved pages DA 42 AFM 3.1. AFM § 1.5 Definitions and Abbreviations 3.1.1. CAS. "Calibrated Airspeed. Indicated airspeed, corrected for installation and instrument errors. CAS equals TAS at standard atmospheric conditions (ISA) at MSL." 3.1.1.1. This definition is not the definition of CAS, but describes how to calculate CAS after reading IAS in the cockpit. As is described in § 2.2.4 above, CAS is much more than the "Indicated Airspeed corrected for the pitot-static position error and the airspeed in- strument errors". CAS is the source of both IAS and TAS. The limiting and the operational airspeeds and the performance of a type of airplane, such as a DA 42, are determined in CAS using a calibrated pitot-static system (in another airplane, or using other flight test techniques). TAS should not be mentioned here, but CAS in the TAS definition, instead. The installation error is normally called position error. This error is due to the position- ing of the pitot-tube(s) on the fuselage in disturbed air, rather than in the undisturbed air in front of the airplane (Figure 2 on page 4). When the pilot needs the calibrated airspeed while in-flight to find performance data in the AFM, or to calculate TAS, he has to add the instrument error (from the calibration report of the indicator) to IAS first, and with this sum, called the instrument corrected airspeed, find the position error in a graph in the AFM. 3.1.1.2. A correct definition of CAS is (§ 2.2.4 above): CAS is the calibrated airspeed in undisturbed air with respect to the standard atmospheric pressure and temperature at sea level. Refer also to the CAS equation in Figure 3. 3.1.2. IAS. "Indicated Airspeed as shown on an airspeed indicator". 3.1.2.1. The IAS as shown on an ASI is the calibrated airspeed comprising the inherent pitot-static position error and the instrument error of the installed airspeed indicator (Figure 2 on page 4). IAS is not the corrected CAS, because the errors are inherent; the pilot does not apply a correction from CAS to IAS. However, for the IAS to be valuable, i.e. to become equal to CAS, the pilot has to add both (positive or negative) errors to the IAS to obtain CAS, for instance the safe rotation speed. The pilot needs to increase or decrease the airspeed of the airplane until the pointer of the ASI indicates the calculated CAS, i.e. the corrected IAS. The IAS indicated by two ASI’s in one cockpit may disagree with ± 4 kt due to different instrument errors. A correct definition of IAS is: ‘IAS is the airspeed indicated on an air- speed indicator and is CAS including the pitot-static position and instrument errors.’ It cannot be said that IAS is CAS corrected for the errors, because there is nothing to cor- rect, the errors are unavoidable. 3.1.3. TAS. "True Airspeed. The speed of the airplane relative to the air. TAS is CAS corrected for errors due to altitude and temperature". 3.1.3.1. Pilots need TAS is for navigation (§ 2.2.2). TAS is calculated from CAS using both the actual ambient pressure altitude and the outside air temperature, using an 15 Harry Horlings, AvioConsult, Airplane Control and Analysis of Accidents after Engine Failure, https://www.aviocon- sult.com/downloads/Airplane Control and Analysis of Accidents after Engine Failure.pdf. 16 AvioConsult, Background information for the definition, theory, flight test and use of VMCA, https://www.aviocon- sult.com/downloads/Background VMC(A) Regulations and Flight Test.pdf Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 21 E6‑B flight computer or an on-board computer. The difference between CAS and TAS is not an error, but is the consequence of not being able to construct a reliable and accu- rate TAS indicator that uses the ambient pressure and temperature at the flying altitude. TAS is the true airspeed of the airplane in undisturbed air with respect to the ambient pressure and temperature. 3.1.4. VmCA. "Minimum Control Speed. Minimum speed necessary to be able to control the air- plane in case of one engine inoperative". 3.1.4.1. VMCA and the flight test technique to measure it in-flight is explained in § 2.5 above. 3.1.4.2. VMCA (as to be spelled i.a.w. CS - Definitions17) is definitely not the "minimum speed necessary to be able to control the airplane in case of one engine inoperative", but is the lowest speed at which the thrust yawing and rolling moments (or motions) can be counteracted with rudder and ailerons after a sudden engine failure and thereafter to maintain straight flight only, provided a small bank angle (max. 5°; the exact magnitude as opted by the manufacturer) is being maintained away from the inoperative engine (CS 23.1493). Not maintaining this small bank angle, for instance by keeping the wings level or during a turn with a larger bank angle, increases the actual VMCA that a pilot will experience in flight above the VMCA that is published in the AFM (Figure 6 above), and hence above the red radial line on the Airspeed Indicator (ASI). The increase of VMCA with the wings level can be 6 kt or more above the published VMCA for a small twin. If the – not indicated– actual VMCA increases above the actual calibrated airspeed of the airplane, control will be lost – by definition and, to most pilots who don't know all about VMCA, also by surprise. In addition, banking away from the small favourable bank angle to either side not only increases actual VMCA, but also the sideslip angle, increasing the drag and reducing the climb performance. As Figure 6 also shows, the rudder deflection needs to be decreased and reversed at a bank angle larger than 5° into the good engine for the sample air- plane, for maintaining the equilibrium of forces and moments, i.e. to prevent the loss of control. 3.1.4.3. The abbreviation VMC is often used, also in CS-23, but CS – Definitions17 defines the Minimum Control Speed, take-off climb, as VMCA (Airborne) to distinguish it from the other VMC's, such as VMCL (landing) and VMCG (ground – take-off run). VMCA (for VMC in the Air or Airborne) not only applies during take-off climb though, but also during the remainder of the flight while one of the engines is inoperative. 3.1.4.4. Many accidents happened after engine failure during take-off when the pilot decided to return for landing as soon as possible, and turned the engine-out airplane at low speed and altitude right away to the downwind leg in the traffic pattern, rather than climbing straight ahead first until reaching a safe altitude where the airspeed can be in- creased (with >20 kt) and single-engine turns can be made safely. 3.1.4.5. When the airspeed is as low as or just above the AFM-published VMCA, near full rudder is already required for counteracting the asymmetrical thrust yawing moment, and less or no remaining rudder is available for directional control during a turn. As the turn is initiated, control will be lost immediately. It also happened that pilots did not apply adequate rudder to stop the yaw, to maintain the heading; partial rudder increases the actual VMCA as well (a higher airspeed is re- quired for an adequate rudder side force to act against the same thrust yawing mo- ment). This often caused the Loss of Control and casualties as well, because of the low altitude from which recovery is not possible before colliding with the ground. This also 17 EASA CS - Definitions, https://www.easa.europa.eu/en/downloads/1674/en, Section 2. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 22 occurs during engine-out training. Refer to the YouTube video by AvioConsult18, and to the report in footnote 15 on page 20 in which such an accident with an EMB-120 is re- viewed and analysed using FDR data and an animation video. 3.1.4.6. CS 23.149 allows the manufacturer to determine VMCA during straight flight with either the wings level or with a small favourable bank angle of up to 5°. The differ- ences are the magnitude of VMCA and the remaining sideslip angle, i.e. drag. Again, when keeping the wings level, the actual VMCA is higher than VMCA when maintaining a small bank angle away from the inoperative engine; the sideslip angle can be up to 14° hence, the drag is also higher, decreasing the remaining rate of climb (§ 2.5.9 above). There- fore, the manufacturer should publish the bank angle that was used to size the vertical tail, to determine VMCA, and for minimum drag together with VMCA and other V-speeds, such as V2, VYSE and VXSE, in the AFM. 3.1.4.7. An improved definition of VMC or VMCA, that complies with airplane design methods (sizing the vertical tail) is presented in § 2.5.27 above. 3.1.4.8. It is strongly recommended to include the following WARNING: Use up to full rudder to maintain straight flight. Do not initiate a turn away from the small favourable bank angle while the asymmetrical thrust is maximal and the airspeed is, or is close to VMCA. Not only the loss of control is imminent, climb performance might become less than positive as well. The AFM-published VMCA is not a safe minimum air- speed for making turns at full asymmetrical thrust, but is safe for straight flight only while maintaining the small bank angle away from the inoperative engine. 3.1.5. VSSE. "Minimum Control Speed for Schooling. Minimum speed necessary in case of one engine intentionally inoperative / idle (training purposes)". 3.1.5.1. EASA CS/FAR 23.149 (d) define VSSE as "a minimum speed to intentionally ren- der the critical engine inoperative that must be established and designated as the safe, intentional, one engine-inoperative speed". VSSE, the Safe Single Engine speed, is defi- nitely not a minimum control speed ("for Schooling"), but a high enough speed at which an engine can be safely made inoperative just prior to a VMCA demo or engine-out flight training. VSSE is the speed from which the airspeed is slowly decreased down to VMCA while maintaining straight flight (§ 2.5.15 above). If during training the airspeed is not decreased below VSSE, the pilot will not learn to appreciate both VMCA and the manoeu- vring restrictions that come with it. 3.1.5.2. Mentioning the critical engine by the rule makers is incorrect. Pilots should be trained to handle (the airplane after) failure of either engine. Just like VMCA, only one VSSE is to be published that applies for either engine that is to be rendered inoperative. VSSE is calculated by the manufacturer and is not determined during flight testing. 3.1.5.3. VSSE is not published in the DA 42 AFM, only its inappropriate definition. 3.1.5.4. Rendering an engine inoperative means shutting it down intentionally as would occur during an actual engine failure. The AFM of the DA 42 however, does not allow shutting down an engine using the fuel selector valve (CAUTION in AFM § 3.5.3 on page 3-24). When the engine is shut down using the ENGINE MASTER switch, the propeller will also feather which results in controllability that is not realistic after a real engine failure; the actual VMCA will be lower than with an unfeathered propeller. When an engine is left running in flight idle, rather than shut down, the actual VMCA might be higher than the published VMCA because of the increased propeller drag and 18 The Real Value of VMCA – How to Prevent a Dead Engine from Turning into a Killing Engine. https://youtu.be/Wbu6X0hSnBY. Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 23 thrust yawing moment. Control might even be lost at an airspeed above the red lined VMCA. 3.1.5.5. Pilots should realize that rendering an engine inoperative at VSSE does not demonstrate the dynamic motions after a sudden failure as would occur at the lower take-off speed or VMCA. The use of VSSE as "minimum speed" does not provide realistic engine failure dynamics and control "for schooling". 3.1.5.6. When it is not allowed by the manufacturer or owner to shut down an engine for a VMCA demo, a power level or an RPM/load% that equals the drag of an unfeathered propeller should be made available and used during the demo. This RPM/load% is not provided in the DA 42 AFM. 3.1.6. VYSE. "Best Rate of-Climb Speed for one engine inoperative". 3.1.6.1. For VYSE to be the "Best Rate of-Climb Speed for one engine inoperative", also a small bank angle away from the inoperative engine is required. This bank angle is smaller than for VMCA because VYSE is a little higher than VMCA, and should be mentioned in the legend of single engine performance graphs. See further § 4.16.1 below. 3.1.7. VXSE, VREF and VR are not defined in AFM § 1.5. 3.1.8. Please use upper- and lower-case letters correctly in abbreviations throughout the AFM. All V's (Velocities) should be capitalized (EASA CS-Definitions17). 3.2. AFM § 2.2 Airspeed 3.2.1. Column IAS. In the table in this paragraph and throughout the AFM, limiting and opera- tional airspeeds are presented as KIAS. This suggests that the position and instrument errors are accounted for in the airspeed indication system of the airplane, but this will not be the case. A few remarks: 3.2.1.1. Airspeeds are indicated on the display of the Garmin G1000 Integrated Avion- ics System and on the mechanical back-up Air Speed Indicator. 3.2.1.2. As described in § 2.3.10 above, IAS is equal to CAS + the position error of the pitot-static system + the airspeed instrument correction. Unless the “instrument” errors of the Garmin 1000 and the backup ASI are zero or exactly the same, the IAS's displayed on both systems are not equal. Therefore, the question can be raised for which system the IAS in the table in AFM § 2.2 applies, for the G1000 or the back-up ASI? And also, for which G1000 and back-up ASI serial numbers (§ 2.3.10). CAS data would apply to both systems, and to all airplanes of the same type. 3.2.1.3. CS 23.1581 (d) requires "All Aeroplane Flight Manual operational airspeeds must, unless otherwise specified, be presented as indicated Airspeeds". The consequence of requiring IAS in an AFM is that each individual copy of an AFM will be unique, because of unique instrument errors and, as many of these speeds are pub- lished on "approved" pages, each AFM-copy requires approval by EASA/FAA as well. Im- agine a series of 500 airplanes sold of the same type and configuration, then EASA will have to approve the indicated airspeeds in 500 AFM's, rather than in only one, the type- specific AFM in which CAS is used. When during maintenance an ASI is removed and re- placed, the IAS might also change when the instrument error differs from the error of the replaced instrument, which would require EASA/FAA approval again. See also § 2.3.16 above. The requirement is not in agreement with CS 23.1587 (d) (10), next paragraph. 3.2.1.4. CS 23.1587 (d) (10) requires "The relationship between IAS and CAS deter- mined in accordance with CS 23.1323 (b) and (c)", but only for commuter category aero- planes. So, the question is whether the airplane is certified and in use in the normal or utility, or in the commuter category. When the airplane is in use for training pilots for a Limited Review DA 42 Airplane Flight Manual AvioConsult Copyright © 2023 – 2026, AvioConsult. All Rights Reserved 24 professional career as airline pilots, then commuter category requirements should apply to teach the pilots all aspects of operating a multi-engine airplane, hence CAS should be used in the AFM. 3.2.1.5. As already mentioned in § 2.4.1 above, the use of IAS throughout an AFM raises the question whether the writer of the AFM knows the instrument error of an in- dividual ASI in a particular airplane. The answer is, he cannot; he obviously considered the instrument error to be zero as inappropriately ‘recommended’ by GAMA. The man- ual writer can only have airspeed data in CAS which are provided by the flight test de- partment, the airplane design engineers, and the performance engineers, including the position error of the pitot-static system following its calibration during flight-testing, which applies to the same series of an airplane type. The instrument errors of each indi- vidual ASI or air data system are not known to the writer, because these vary with each instrument or air data system. GAMA recommends the use of IAS, and hence of a zero- instrument error, but this is definitely not in compliance with FAR 23. A small instrument error or air data conversion error has a large effect on the control power of rudder and ailerons at the limiting and operational airspeeds (§ 2.4.4 above). So, in a common AFM that applies to a series of airplanes of the same type, IAS cannot be used, unless the air data computer allows the entry of position correction data of the pitot-static system and of the instrument and/ or pressure conversion system errors, in- cluding updating after maintenance-replacement and calibration. The stall speed, VMCA and other speeds in CAS are the same for all similar types (tail num- bers) of airplanes for which the