Airworthiness Bulletin AWB 85-025 Issue 5 – 12 August 2021

requirements listed in the global aviation gasoline standards. Figure 5 – Lead Content vs. Aromatic Content (Source CRC Report No. 657 Rev. A, May 09, 2011, Page 46) AWB 85-025 Issue 5 12 August 2021 Page 5 of 13 Test Program - The test program compared the operating characteristics of a current configuration O-360-J2A engine on several fuels while instrumented to enable comprehensive data acquisition and analysis via a proprietary system made by AVL, Austria. The program was conducted at various engine speed (RPM), engine power (OBHP) and temperature operating points and environmental conditions including hot conditions at cylinder head, oil temperature and induction air limits, as follows. Hot Condition Temperature Targets Hottest Cylinder Head 500°F - 510°F (260.0°C – 265.6°C) Oil Gallery Temperature 245°F - 255°F (118.3°C – 123.9°C) Induction Air Temperature 103°F - 109°F (39.4°C - 42.8°C) Figure 6 – Hot Condition Temperature Targets The magnitude of changes in Cylinder Head Temperature (CHT) and exhaust Gas Temperature (EGT) need to be assessed against the inherent variability in engine operating parameters. Slight variations in engine speed, fuel flow, mixture distribution to each cylinder, and cycle-to-cycle combustion have an impact on the system. Even with the engine running at steady state conditions on US 100LL avgas, the measured CHTs and EGTs fluctuated within an operational tolerance of 4°F and 10°F respectively. A consistent directional trend in EGT was noted between AU 100LL and AU 100/130. With the exception of the 2700RPM, 145 OBHP, hot conditions set point the temperature change across all cylinders was within the EGT operational variability discussed above. No directional trend was noted in the change in CHTs with the temperature changes across all cylinders and at each test point, within the CHT operational variability tolerance. The measured change in EGT of approximately 20°F (11.11°C) during the hot conditions test phase, remains within the typical variation expected during normal engine operation. Changes in EGT can be expected with changes in engine power setting alone. For example, during the transition from a test point at 2700 RPM, 145 OBHP to 2652 RPM, 131 OBHP, (9.7% change in horsepower) the steady state temperature of EGT 2 and EGT 3 changed by an average of 31°F and 23°F respectively. Additionally, the sensitivity and variability in EGT is demonstrated in Figure 7 – Mixture Distribution Sweep, where manual leaning from best power to best economy results in an EGT increase of approximately 150°F. This is typical for the same cylinder head and valve configuration used in fixed wing applications. AWB 85-025 Issue 5 12 August 2021 Page 6 of 13 Figure 7 – Mixture Distribution Sweep It is recognised that a variation in EGT can be anticipated when switching between fuels possessing different aromatic contents. However, for a fuel that meets the Avgas specifications where the aromatic content only varies from 0–18% v/v the magnitude of the change in EGT values has been demonstrated to be minimal and not expected to have an impact on the operation or durability of an engine, on its own. Avgas Low Lead Future There is a limit to which the effect of reduction in lead (tetraethyl lead) may be offset by the base alkylate and aromatic content to achieve the required Motor Octane Number (MON) for the fuel. Historically, the lead concentration typically must exceed 0.28Pb, g/L. With lead being a toxic substance that can be inhaled or absorbed in the bloodstream, alternative unleaded fuel formulations are being explored. This effort is being led by the Piston Aviation Fuels Initiative (PAFI) research program as a partnership between the FAA, aircraft and engine manufacturers, fuel producers, the EPA and industry associations. AWB 85-025 Issue 5 12 August 2021 Page 7 of 13 For CASA, flight safety is of paramount importance in any switch to alternative fuels. Until a viable unleaded replacement fuel is found and certified, the current position will remain unchanged. It also needs to be recognised that the piston aviation fleet in Australia inevitably has to transition to an economical viable unleaded future. In that regard CASA will be guided by the outcome of the PAFI program, the implementation strategies promulgated via the Federal Aviation Administration Unleaded Avgas Transition Aviation Rulemaking Committee, the ASTM International fuel specification and associated legislative requirements passed by the Australian government. 6. Recommendations A. Operating Procedures and Limitations Pilots should observe the following precautions: Perform a complete run up and stabilised hover check prior to every flight. Do not initiate flight if there is an indication of engine rough running, induction backfire or sudden airframe yaw. If any of the above symptoms are experienced during flight, discontinue the flight, and have an appropriately Licensed Aircraft Maintenance Engineer (LAME) check valve condition. The LAME should listen for sound of leakage at each intake valve while performing a differential compression test in accordance with the latest revision of Lycoming SI No. 1191. A cylinder borescope inspection should also be performed as outlined in paragraph ‘C’ (below) Note: If a leak path past an intake valve is detected, contact Lycoming Technical Support for further guidance. Refer to Lycoming SI No. 1577 for additional information and reporting requirements. Aircraft Performance Limitations Air cooling alone, may be insufficient to adequately cool all cylinder components in some elevated temperature operating environments. For the above reason, it is critical that all aircraft operational and performance limitations as given in the applicable aircraft Pilot’s Operating Handbook (POH) and Engine Operation Manual are strictly observed. Powerplant limitations are given in Section 2 of the Robinson POH which identifies the Cylinder Head Max Temperature as 500°F (260°C). The colour code instrument markings for the Cylinder Head Temperature (CHT) identifies the Green arc from 200 to 500°F (93 to 260°C) with the Red line at 500°F. AWB 85-025 Issue 5 12 August 2021 Page 8 of 13 The edge of the Red line identifies the operating limit and the pointer should not enter Red during any normal operations. These limitations need to be considered concurrently with the applicable Lycoming Operations Manual which states: − Never exceed the maximum red line cylinder head temperature limit, and − For maximum service life, cylinder head temperatures should be maintained below 435°F (224°C) during high performance cruise operations and below 400°F (205°C) for economy cruise powers. Furthermore, Section 5 of the POH provides the following pertinent details on aircraft performance relative to operating temperatures: − Satisfactory engine cooling has been demonstrated to an Outside Air Temperature (OAT) of 38°C (100°F) at sea level or 23°C (41°F) above ISA altitude. Note: All associated aircraft performance data presented in the POH which is charted against OAT is limited to +40°C (+104°F). Figure 8 shows a scatter chart of maximum OAT’s from Engine Data Management (EDM) systems installed on Robinson Helicopters operating in Australian regions north of the Tropic of Capricorn. The following items should be considered to reduce the impact of “hot” operations: • Ensure operating parameters meet charted values. • Fly the aircraft in accordance with the manufacturer’s guidelines. • Avoid manoeuvres which may interrupt/distort relative airflow for engine cooling. • Plan operations around the coolest time of the day. AWB 85-025 Issue 5 12 August 2021 Page 9 of 13 Figure 8 - Maximum OAT (°C) per Flight Be aware that there is a cumulative effect of elevated temperatures on cylinder assemblies which will degrade the properties of those materials over time. Even a cylinder displaying a moderate CHT, can be suffering accelerated wear. Be mindful that a single probe CHT will not necessarily be indicative of all cylinders, nor represent even and consistent cooling of the entire cylinder assembly. CHT is also not necessarily indicative of actual valve temperatures. (°C) For maximum service life of the engine, Lycoming recommends: − maintain CHT between 150°F and 435°F, during continuous operation, and − prior to engine shutdown idle until there is a decided decrease in CHT. AWB 85-025 Issue 5 12 August 2021 Page 10 of 13 Operating Factors Intake valve deposit formation, wear and leaks may also be aggravated by: - ‘Hot Loading’ and/or ‘Hot Refuelling’ (extended ground operations) in high ambient temperature conditions. It is therefore recommended that wherever possible these operations are avoided or limited. - Inadequate engine cool down prior to engine shutdown. It is recommended that an extended cool down regime is initiated to ensure that engine CHT is as low as reasonably practical prior to engine shut down. This may require several minutes of run time to maximise the benefit. If the ambient ground air temperature conditions impact a pilot’s ability to induce an adequate drop in CHT prior to engine shut down consideration should be given to suspending operations. NOTE: Robinson has published a HOT CLIMATE COOL DOWN PROCEDURE for insertion within Section 4 of the POH to avoid potential unintended consequences resulting from inadequate engine cooldown during aircraft operations in hot climates. B. Oil Type/Grade Analysis has verified that the coke-like deposits on the convex side of intake valves was primarily derived from residual lubricating oil, (not fuel or air-borne contaminants). Coking can form as a thin-film layered deposit (varnish or staining) or in thick clumps. Determining the initiation source of coke formation is difficult as it can be attributed to a combination of influences including, but not limited to. • operational conditions such as hot shutdown • exposure to abnormally high conductive or convective temperatures • prolonged aircraft inactivity leading to moisture absorption of coke deposits. As indicated in Figure 7 there can be a wide variation in operating temperature. Selecting a high viscosity straight weight oil due to high daytime ambient temperatures may exceed the low temperature range of the oil during colder, early morning engine starts. Additive packages in multigrade oils extend the operating temperature range and provide superior lubrication of the engine. To determine what grade of oil to use refer to the latest revision of Lycoming SI No. 1014 – “Lubricating Oil Recommendations”. C. Maintenance Cylinder Borescope Inspection Implement regular borescope inspections as a first line of defence in detecting the onset of valve problems. The cylinder borescope inspection enables timely and direct visual examination of the internal cylinder components and should be used in conjunction with the “Differential Pressure Test” to assess the condition of the valves to identify visual signatures and abnormal operating patterns. AWB 85-025 Issue 5 12 August 2021 Page 11 of 13 1. With the spark plugs removed, position the piston at bottom dead centre at the end of the intake stroke. 2. Insert the borescope through the upper spark plug hole and inspect the intake valve and valve seat. 3. Inspect for signs of leakage or damage indicated by localised discolouration or erosion on the valve face and seat circumference. See previous example images. 4. Remove intake pipes and move the piston through the intake stroke whilst observing the valve through the intake ports. 5. Inspect for accumulation of carbon deposits around the valve stem, guide and fillet. See Figure 8. 6. Deposit formation may also impact valve rotation which is essential to valve longevity. Valve rotation assists in equalizing the heat load around the circumference of the valve face and helps keep the valve and seat clean and free of deposits. A build-up of deposits will ultimately impact heat transfer efficiency with a consequential increase in localised temperature and hot spots. If you find a burnt/damaged valve, closely inspect the valve tip (where the rocker arm contacts the intake valve) and associated rocker arm ‘toe’ for linear wear marks, (indicating limited or no valve rotation). NOTE: In order to improve valve seating and minimize compression loss, a new intake valve, incorporating a rotator cap is available by retrofit in accordance with Lycoming SI No. 1280, Revision D. Alternatively, Cylinder Kit No. 05K29866 can be procured which includes the new rotator type intake valve configuration. Lycoming have also advised that new and aftermarket O-360-J2A and O-540-F1B5 engines shipped from Lycoming will have this new rotator type intake valve configuration incorporated. 7. Report all borescope inspection findings, including nil defects, to CASA per Section 7, (below). Maintenance considerations to maximise engine cooling efficiency: • Cooling scroll inlet metal lips-to-fanwheel clearance is within Maintenance Manual specification. • Mixture control at carburettor is at full-rich position when mixture knob is fully in. Figure 8 - Valve Intake Port AWB 85-025 Issue 5 12 August 2021 Page 12 of 13 • Integrity of engine baffles and cooling panels. • Cooling hoses are properly routed, secured, and in good condition. • Correct spark plugs (Lycoming SI No. 1042 refers). • Magnetos are properly timed. • Integrity of exhaust riser-to-cylinder head gaskets • CHT gauge calibration Strict adherence to the aircraft and engine manufacturer’s maintenance schedule together with associated instructions for continuing airworthiness is essential for optimum performance and longevity of the engine. Cylinder Assembly In-house Repairs All maintenance involving the valves, valve seats and valve guides must be performed to a high precision standard to avoid concentricity/perpendicularity issues and suboptimal valve contact with seat face. If valves require refacing, remove the minimum amount of material to clean up pits in the valve face or to correct any apparent warping condition. After refacing the total runout of the valve face and edge thickness must be within Lycoming published limits. Whenever a new valve seat is installed, its matching valve guide must be replaced. This will assure concentric grinding of the new seat. Refer applicable engine Overhaul Manual for valve seat replacement instructions, dimensional limits, and necessary tooling. 7. Reporting Report all instances of premature intake valve and valve seat degradation to CASA via the DRS system available on the CASA website. Details of the maintenance history for the engine should be provided in addition to information concerning the method of failure detection, the location and condition of the defective parts in addition to modification status. Operational parameters should also be reported i.e., OAT, RPM, MAP, CHT, Oil Temp, Est. Fuel Burn (lbs/hr) together with any other information on possible triggers for the reporting of occurrences involving an engine backfire or aircraft yaw/twitch event. This information will facilitate a detailed review of potential failure causes and contributing factors. AWB 85-025 Issue 5 12 August 2021 Page 13 of 13 8. Enquiries Enquiries with regard to the content of this Airworthiness Bulletin should be made via the direct link email address: AirworthinessBulletin@casa.gov.au or in writing, to: Airworthiness and Engineering Branch National Operations and Standards Civil Aviation Safety Authority GPO Box 2005, Canberra, ACT, 2601