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E.R.A.U. LIBRARY
AIRCRAFT ACCIDENT REPORT. REXALL DRUG AND
CHEMICAL COMPANY. LEAR JET 23, N235R.
CLARENDON, TEXAS
NATIONAL TRANSPORTATION SAFETY BOARD, WASHINGTON, D.C 23 APR 1966 Doe NTSB
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. 67 U.S. DEPARTMENT OF COMMERCE AE, National Technical Information Service SA-None I . ,
AIRCRAFT ACCIDENT REPORT
Adopted: December 19, 1967 REXALL DRUG AND CHEMICAL COMPANY LEAR JET 23, N235R Claren_don, Texas April 23, 1966 NATIONAL TRANSPORTATION SAFETY BOARD.
DEPARTMENT OF TRANSPORTATION WASHINGTON D.C. 20591
U.S. c::~~~~~:~:;...~, ,ma
~tlon~I Te~hnlcal lrlr.rmailon $trvl~1 Springfi1ld, Vlrgi11i1 211'1
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DATE EVALUATED -, U.S. OH'ARTMENT OF TRANSPORTATIOL-!
FE.OERAL HIGHWAY ADMINISTRATION RESEARCH AND DEVELOPMENT REPORT OUFH-'.AU OF PUBLIC ROAD:J
November 10, 1970 I
ABSTRACT ANO EVALUATION 1. STATE 2. ST ATE'_:; ,STUDY NO.
13. SPA ADMIN IDENT NO, .
. B-l-b3 Florida
23'7.0
4. STUDY TITL,,E Hesearch on Asphaltic Materials S. REPORT Tl TL E 6. AUTHOR(Sl H. E. Schweyer, Principal Investigator Research on Asphaltic Materi_als-- .. ,a,., .• J. C. Busot, Co-Principal Investigator • terminal Report ..
CC...------1 7. Rao DIVISION TO WHICH ASSIGN ED B. PROGRAM AREA Materials 4671-052 9. STUDY CONDUCTED BY • rU_n_i_v_e_r_s_i_t~y_o_f_· _F_l_o_r_i_d_a~-----·-· ----,----.,..,---------·-----------'---I -10. SPONSORING AGENCY: Florida Department of Transport at ion I 1. TYPE OF R6D: D THEORETICAL lfxlAPPLIED □ DEVELOPMENT 0MT6E □ OTHER R60 ' 12. STUDY STATUS ___ 6 YEAR OF' A ___ 6 YEAR STUDY □ ACTIVE ~ COMPLETE .~ JtJ!;J'TRACT ORIGINAL SY~ Authors IEDITEDl~BY: rJ_.~M~._R_i_c_e ___ ~--- Th,ii\s_ terminal report includes summar1e s of reports submitted during the course of a 6-year laboratory study of selected asphalt cements. Also included is an updating of basic rheological and· compositional information on several asphalts and a rheological evaluation developed using an Instron extrusion t'.echnigue. Rheological responses were studied by a computerized cluster analysis technique. This analysis was extended to durability responses using the Thin Film Oven Test and a special Weatherometer test, The clt.:s,:er technique enables classificatic;m of asphalts in groups with similar respon- ·. ~~t,~e !~:.~;~!!.~;~;.:~i~! .;~~;:.::~/4;) with leve_ls of perf_o~ance could pos~ibly b<e of •
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Other contributions m.ade during t~e course of the study were: (1) creep test data on asphalts at low temperatures for evaluation of viscoelastic behavior, and the prelim- inary development of a compression test for rheological tests over a wide range of temperatures; (2) comparative data of rheological responses in the sliding plate, cone- and•pl ate, and extrusion rheometer. providing information about the relative merits of these instruments which deform asphalt in different geometries; (3) new procedure for I composi.tional analysis and chem'ic.al evaluation of components; (4)_ Weath.ero. me. t_er proce.d-1 ure for use in co_njunction with the Thin Film Oven Test for the study of the response .:
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14. STATE HOW THE RESULTS OF THIS RESEARCH CAN SE USED OR APPLIED. The f'indings of the study are primarily of interest to .researchers involved in studies associated with rheology>dura- bility, and composition of asphalt cements. The applicability of the findings to the behavior of as halt in avements still has to be ascertained rior to any specific~tion 1s. COMMENTS: /formulation.
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TECHNICAL CCOROINATOR. DIVISION, REGION OR R&O DIVISION REXALL DRUG AND C!IDITCAL COMPANY LEAR JEI' 23, N235R CIARENDON, TEXAS APRIL 23, 1966 TABLE OF CONTENTS Page Synopsis , , , , ...... , ... , ................... .
l 1. Investigation ............................. .
1.1 History of Flight ................ ; ........ .
1. 2 Injuries to Persons , ....................... .
1. 3 Damage to Aircraft ....................... ..
1. 4 other D3mage .............................. .
1.5 Qrew Information .......................... .
1. 6 Aircraft Infonnation ...................... . 4 1,7 Meteorological Infonnation ................ .
1.8 Aids to Navigation : .................... • ... .
l. 9 Communications .... • ........................ .
1.10 • Aerodrome and Ground Facilities ....... : ... .
1.11 Flight Recorliers .......................... .
1. 12 Wreckage ................................ , .. 8 1.13 Fire ........... , .......................... . 11 1.14 Survival Aspects ......................... ..
1.15 Tests and Research ......................... . 11 1. 16 Other ...................................... .
2-. Analysis and Conclusions .................. .
2.1 Analysis ................... • ............... .
2.2 Conclusions ............................... .
(a) Findings ............................. .
(b) Probable Cause ....................... .
3 . Recommendations ........................... . 16 . / ., ...
" "_j ·' File No. 2-ll79 NATIONAL TRANSPORTATION SAFErY BOARD DEPARTMENT OF TRANSPORTATION AIRCRAFr ACCIDENT REPORT Adopted: December 19 1967 REXALL DRUG AND CHEMICAL COMPANY LEAR JEr 23, N235R CLARENDON, TEXAS APRIL 23, 1966 SYNOPSIS ~A Rexall Drug and Chemical Company Lear Jet, N235R, crashed approxi- mately 1.5 miles southwest of Clarendon, Texas, at about 1238 on April 23, 1966. Both of the crewmembers were fatally injured. There were no passengers. The aircraft was destroyed.
The flight, for the purpose of'issuing a type rating to the pilot, was returning to Fort Worth from Amarillo, Texas. During an unrestricted climb to Flight Level 410, there were numerous routine communications between various air traffic control facilities and the flight. The last intelligible transmission WJilS an acknowledgement of instructions to change radio frequencies, at approximately 1234. About 54 seconds later an open microphone carrier tone, lasting 15.5 seconds, was received from the air- craft. At 1235:40 the radar target from the aircraft disappeared. The weather existing at the time of the accident included cirrus clouds and moderate to severe turbulence associated with a jet stream with wind velocities in excess of 75 knots.
The Board determines that the probable cause of this accident was the loss of control of the aircraft, in turbulent, instrument conditions, which could have been caused by a failure of both gyro horizons. ( ). ,,., ' \- - 2 - 1. INVESTIGATION 1,1 History of the Flight A Rexall Drug and Chemical Company Lear Jet, N235R, arrived at Amarillo, Texas, at 1112I/ on April 23, 1966. There were no reported discrepancies with the aircraft, The pilot and the Federal Aviation Agency (FM) Operations Inspector, who was giving the pilot a flight check for a tYJ)e rating, proceeded to the Flight Service Station (FSS) where a weather briefing was received. An Instrument Flight Rules (IFR) flight plan was filed to Fort Worth, Texas, via selected airways to Bridgeport, Texas, and then direct to the Fort Worth outer marker. The estimated time en route was 45 minutes, with a true airspeed of 440 knots at Flight Level 410 (FL 410). During the taxi-out the flight was issued a clearance as filed.
At 1226 the flight departed on Runway 3, with instructions to maintain runway heading for a vector.to J-58, the initial airway. At 1231:30, the flight was 21 miles east of the Amar~llo VORTAC, and control of the flight was transferred to Albuquerque Air Route Traffic Control•Center (ARTCC). Ten seconds later they i;-eported leaving FL 240. At approximately 1234 a radar hand- off was effected 38,miles ~om the Amarillo VORTAC, and the flight acknowledged the new frequency for the Fort Worth Center. At 1234:54 an open microphone sound began on the Albuquerque frequency and lasted 15.5 seconds.
The Fort Worth Center controller who had assumed control responsibility for the flight was observing the progress of the aircraft radar target along J-58, while awaiting the initial radio contact from the flight. At 1235:40 the secondary radar (beacon) target from N235R disappeared. The controller instantly 1/ All times herein are central standard, based on the 24-hour clock, - 3 - turned up the primary radar gain in order to locate the aircraft "sk:'..:1 paint" but no target was observed. Radar contact was lost about nine miles east of the impact site. A flight check revealed that the minimum altitude for both primary and secondary radar coverage in this area is 20,000 feet.
The aircraft crashed 1,5 miles southwest of Clarendo:1, Texas, at approxi- mately 1238, during daylight. The geographic coordinates are 34°55'6" N.
latitude and 100°54 13" W, longitude, and the elevation at the crash site is 2,820 feet m.s.l.
Witnesses in the area reported hearing the aircraft making a loud, shrill, , noise before they observed it. Some also heard one or two booms which they associated with a sonic boom. They generally agreed that the sky was overcast, and reported good visibility althoug9 it was raining. Witness observations of the aircraft were inconsistent and no meaningful flightpath was established from this source.
1.2 Injuries to Persons Passengers Others Injuries Crew Fatal 2 0 0 Nonfatal 0 0 None 0 0 1.3 Damage to Aircraft The aircraft was destroyed by impact.
1.4 Other Damage None 1,5 Crew ~nformation Pilot William M. Majowski, age 28, held airline transport pilot certificate •., No. 1433989 with a rating for airplane multi-engine land and commercial privileges - 4 in airplane single engine land. His FM first-class medical certificate was issued February 11, 1966, with no limitations. He was hired by the Rexall Drug and Chemical Company on June 7, 1965. Company records indicate that he had accumulated 2,554 total flying hours of which 380 hours were in the Lear Jet.
Operations Inspector James D.,Sweep, age 45, held airline transport pilot certificate No. 385428 with ratings in the DC-3 and Lear Jet Model 23, and commercial privileges for airplane single engine land and sea, and flight instructor.
His FAA first-class medical certificate was issued April 18, 1966, with the limitation that, "Holder shall possess corrective glasses for near vision while exercising the privileges of his airman's certificate."
He was.employed by the FM in July, 1961, and had accumulated 8,387 total flying hours of which 529 hours were in jet aircraft and 48 hours were in the Lear Jet. He attended ground school at the Lear Jet facility in Wichita, Kansas, received flight training from Executive Jet Airways, Inc., Columbus, Ohio, and was issued .a type rating in the Lear Jet Model. 23 on May 28, 1965.
He was conducting hi's tenth type rating check at the time of the accident.
Statements obtained from tμe previous applicants he had checked indicate that all flights were conducted in accordance with established procedures.
1.6 Aircraft Information N235R, a Lear Jet Model 23, serial number 23-032, was manufactured on June 24, 1965, and at the time of the accident had accumulated a total of 436.7 hours. It was maintained in accordance with FM requirements. The last 100-hour inspection was completed April 20, 1966.
- 5 - The aircraft was equipped with two General Electric Model CJ-610-4 engines installed as follows: Position Serial No.
Total Time 241006 241003 The aircraft was serviced with A/50 type jet f'uel and anti-icing additive, The approximate gross weight at takeoff was 11,668 pounds, well below the allowable of 12,500 pounds, The center of gravity was at 25,0 percent, which is within the allowable limits of 16 - 31.5 percent, 1,7 Meteorological Information The Weather Bureau (WB) aviation area forecast prepared at Fort Worth, valid for the 12-hour period begin¢ng at 0700 was in part as follows: Weak, nearly stationary, front near Fort Smith-Waco line Westwaid will move little during day. Widely scattered thunderstorms developing• northwestern Texas during early morning, will spread into central Oklahoma by 1900. North and west of front generally ceilings 300-6oO overcast, 1-3 miles light drizzle, fog, locally ceiling zero, sky obscured, ' • light· drizzle and fog, Variable layers to 20,000 feet. Cumulo- nimbus tops to 45,000 feet. Conditions improving by late morning to ceiling 800-1, 500 feet overcast, 2- 5 miles, fog, occasional light drizzle with scattered thunderstorms, light rain showers.
Moderate, locally heavy, icing in cumulonimbus and occasional moderate rime icing in clouds elsewhere above freezing level Severe turbulence all levels near thunder- 11,000-12,000 feet, ' storms.
- 6 - The 06:JO chart for the 300 mb. level (approximately 30,000 feet) showed a broad southwesterly flow of air over the Southern Plains and a double jet stream structure. One jet stream was shown· extending, in part, from south- western New Mexico northeastward to southwestern Minnesota, and the other extended from extreme southeastern New Mexico to just east of Amarillo, thence northeastward through the accident area. The winds associated with both streams were in excess of 75 knots.
The 1200 winds aloft observation at Amarillo was, in part, as follows: Heigl)t (m.s.l.)
Direction (True) Velocity 25,000 feet 220 degrees knots 30,000 32,000 35,000 38,000 40,000 At the time of the accident WB criteria for forecasting severe turbulence included vertical win~ shear in excess of 6 knots per 1,000 feet and horizontal shear greater than 4o."knots per 150 miles·· in association with a jet stream.
' .
The 1245 observation on the Amarilio WSR-57 wea~her radar showed that the accident site was in a broken area of ·echoes.from light rain showers reaching the surface, and thunderstorms with light rain showers reaching the surface.
The.tops of detectable moisture were from 15,000-20,000 feet.
The 1242 special surface weather observation at Amarillo, 4o miles north-
west of the accident, was: Estimated 8,000 feet broken, high overcast, 10 miles, light rain, wind 120 degrees, 9 knots, altimeter setting 30,11, few scud east.
- 7 - The 1239 special surface observaticn at Childress AFB, 42 miles south- east of the· accident was: Balloon ceiling 900 feet overcast, 3 miles, thunderstorm,
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light rain showers, fog, altimeter setting 30.07, pressure falling rapidly.
The freezing level at Amarillo was 11,000 feet.
Pilots flying in the general area at the time of the accident reported turbulence and IFR conditions above FL 310. Additionally, weather satellite photographs of the general area, taken within one hour of the accident, re- vealed dense cirrus clouds of the type frequently associated with jet streams.
These clouds, the conditions described above, and other meteorological data satisfy the necessary criteria, ~s determined by meteorological research associated with high altitude turbulence, to clearly indicate that turbulence of at least moderate intensity existed above the 30,000-foot level.
1.8 Aids to Navigation There were no reported discrepancies wit·h any of the navigational aids.
1-9 Communications All communications between th.e flight and the air traffic control facilities were routine. The open microphone sound, recorded on the Albuquerque center frequency, was analyzed by the Federal Bureau of Investi-
I
gation. They reported that the sound level increases in excess of three
I
volume units from beginning to end, and" ... contains the same general noise distribution as the known transmissions from N235R . . . " and different from the sounds of transmissions from other aircraft recorded on the tape.
- 8 - 1.10 Aerodrome and Ground Facilities Not applicable.
1.11 Flight Recorders The aircraf't was not required to have flight recorders and none were installed.
1. 12 Wreckage The aircraft crashed in gently rolling terrain of relatively soft sandy soil up to two feet deep, with an underlying hard packed crust. The impact left three distinct craters which were interconnected by a narrow scar and aligned on a bearing of 030-210 degrees. Parts of the aircraft were found approximately nine feet deep in the center crater. The bulk of the wreckage was thrown out in a fan shape with a centerline of 210 degrees.
The north and south craters contained parts of the left and right wing tip tanks respectively, and the center crater contained many heavy components from the fuselage. Despite the extefilsive breakup, parts of all major portions of the structure and control surfaces were founp. at the site.
The nose section of the fuselage disintegrated, The largest pieces of pressurized section were a 40-inch length of cabin door surround structure , and a crushed mass of keel beam atta~h fittings, fnselage fuel cell material, and control cables and pulleys. The tail ,cone was represented largely by three pieces of skin and stringers ranging from four to six feet in length.
Plastic material from the windshield and windows was recovered from the center crater. No piece had a maximum dimension of over four inches, and most pieces were delaminated or pulverized. The complete upper and - 9 - lower cabin door hinges were fo\illd attached to portions of t~e cabin or door structure.
The wings were generally fo\illd as small pieces of upper and lower skin, separated access plates, short sections of spar caps and webs, and heavy fittings. The largest piece of wing was a four by five-foot section of the left wing skin.
The horizontal stabilizer separated into t_wisted pieces of spar cap, relatively large pieces of interspar skin panels, and individual fittings.
The left boss .of the stabilizer hinge forging failed and the hinge pin had separated from the right boss. The failed parts of the stabilizer attach and h!inge fittings were examined carefully. All fractures, cracks, brinelling, etc. appeared to be typical of failure resulting from gross overloads. There was no evidence of any repeated impact on the stabilizer structural up-and-down stops.
The recovery and identification of parts of the control surfaces varied from 70-100 percent, except the ailerons which were too mangled to estimate.
Almost the .entire spanwise length. of both elevators was identified.
The left elevator was in_ four pieces ranging in length from nine inches at the tip to 30 inches at the inboard end. The right elevator was in two main pieces, one 73 inches long and another nine inches long. Four of the five elevator hinge brackets and part of the fifth were identified. These were separated from the surrounding structure. The bearing in one outboard bracket turned freely, but the others were missing or damaged. The elevator and rudder co\illterweights were never identified although one small piece of
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- 10 - lead was found which was not associated with the aileron weigits. The trailing edge strips which are glued to all primary control surfaces separated, and little of this material was found.
The horizontal stabilizer jackscrew • was less thar. one-half turn from the full aircraft nosedown stop, which is the normal range. The aileron and rudder electric trim actuators were compared with undamaged units, and each was found to be in a near neutral position.
The spoiler actuators were fully retracted, which is the spoilers down position. The wing flap actuator was torn from its attach points. The landing gear actuators for the left main gear and nose gear were in the gear up position. The right main gear actuator was in the midpoint position.
The rotating components of both powerplants disclosed moderate to heavy rotational damage. None of the bearings examined exhibited evidence of operational distress, nor was any evidence of fire or operation at ele- ., vated temperatures found.
Both starter-gen~rators were recovered and exhibited similar rotational damage to the rotor housings. The two batteries were heavily damaged, but the g_uick disconnect fittin,gs were still attached to the battery posts.
V • The two static inverters were destroyed by impact .. However, the eight P/N 2359 transistors were examined for evidence of overheat conditions such as would cause the inverters to program off the line. Six of the eight transistors were still operational, but the other two were impact damaged.
None showed any sign of an overheat condition. A standby rotary inverter was examined and showed no evidence of rotational scoring.
t
- 11 - Only one gyro horizon, unidentifiable as to side, was recovered. This attitude indicator revealed impact damage compatible with a presentation of five degrees noseup and ten degrees left wing down. The "power off" warning flag for this instrument is spring loaded to the "power off" position and was impact-formed in this position.
The ·two VOR receivers indicated bearings of 1i8 degrees and 288 degrees, but no determination of "To" or "From" signals could be made. A c·ourse line indicator was recovered and determined to be indicating an aircraft heading of 180 degrees.
The rotary-type vertisyn and directisyn source selection switches were found in the primary position. These switches allow the pilot to select the secondary or copilot's gyro or directional information to be displayed on his instruments if the primary system is inoperative.
1.13 Fire There was no evidence of f~re on any part of the aircraft or on the ground in the· impact area.
1.14 Survival Aspects • This was .a nonsurvivable accident.
1.15 Tests and Research A review of the flutter substantiation disclosed that it was based on ground vibration tests and analysis. The aircraft was calculated to be
g/
free of flutter to speeds in excess of 1.2 Vn/Mn (400 knots to 20,500 feet and 0.90 Mach above). Flight flutter tests had been conducted to 386
gJ vJMn ~efers to the design dive speed or Mach number for the
particular regime of flight.
- 12 - knots and 0.86 Mach. Static balance of the elevator was provided by weights in the tip overhang. Production balance limits ·or Oto 0.5 inch-pounds nose heavy on each elevator had been established. The ~lutter speed was highly sensitive to, and rapidly reduced by, increasing amounts of under- balance ( tail heavy).
A questionnaire regarding the operational experience of the electri- cal/instrument system of the Lear Jet was circulated to 73 owner/operators.
Fifty-two responses were received. Fifty percent indicated they had ex- perienced gyro horizon failures or malfunctions, but only six operators attributed the failures to AC power loss.· Several commented further that these AC power losses we·re subsequently found to have been caused by mal- functions in either the vertisyn or directisyn systems. Additionally, 38 percent reported inverter failures. Only four.of the 26 operators reporting gyro failures had accuniulated over l,000 hours on their aircraft. The average service life experience by these operators, for various components, is as follows: Vertisyn 318 hours D~rectisyn 325 hours Static Invefter - 391 hours 1.16 Other AC electrical power is normally developed in the Lear Jet by two 115 volt, 400 cycle static inverters, each capable of delivering 250 volt- amperes. The system is designed to have only one inverter at a time supply power. Either inverter supplies AC power to the 26 volt AC circuit and the
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- l3 - respective primary or secondary bus; however, power to the other bus is available oniy through a bus tie breaker. In addition, N235R had a rotary inverter installed as a standby source of AC powe::-.
From the evidence it is concluded that the Lear Jet, like most high performance swept-wing aircraft, has low inherent lateral directional sta- bility. Accordingly, the aircraft would be difficult to control during operation in turbulent, instrument conditions with the gyro horizon and yaw damper inoperative. The Flight Manual states that the yaw damper must be operative for all flight conditions except takeoff.
2. ANALYSIS AND CONCLUSIONS 2.1 Analysis There was no evidence of inflight powerplant or flight control mal- function. Portions of all control surfaces in the impact area and ~he lack of hammering on the stabilizer up and down stops indicate that no flutter was encountered.
The flight departed normally, entered a broken to overcast cloud deck
at approximately io,ooo feet, and was probably in clouds throughout the
remainder of th~ flight.
' Since there was no climb res~riction imposed, the normal en route climb performance of the aircraft would have placed the flight at approximately FL 330 by 1234. At this time they acknowledged a radio frequency change from the Albuquerque to the Fort Worth Center. Although this transmission was normal, the flight was well above the 30,000-foot altitude at which they ----, - 14 - would have entered the moderate to severe wind shear turbulence associated with the jet stream. The"l5.5-second open microphone carrier signal from N235R was recorded at 1234:54 on the Albuquerque frequency, indicating a disruption of normal cockpit duties shortly after 1234, and before the frequency change was accomplished. Although there was no voice transmission during the carrier signal certain meaningful information was derived. The increase in sound level indicates not only the availability of LC power during the upset, but also the rapid buildup of airspeed at this critical time. The crew's preoccupation with the emergency and subsequent loss of control is evident in that they never accomplished the change to the newly assigned frequency ..
The Board concludes that there was a loss of control of the aircraft which could have been caused by the failure of both gyro horizons during turbulence. While only one was recovered, if the other had not also failed, a cross-check of other instruments,would have quickly identified the re- maining operative.gy,ro horizon and the upset should not have occurred. An unsatisfactory tr.end of in-service failures of the Lear vertisyn package is amply demonstrated in the questionnaire survey of operators. Attempting to , / control the aircraft by means of slcondary attitude reference under turbulent, instrument conditions is an extremely difficult task in this aircraft. The gyro horizon failures may have resulted from an AC power failure; however, the rotary-type vertisyn and directisyn selector switches were in the pri- nary position, and the third inverter was not rotating at impact. This does not preclude the possibility of progressive electrical difficulty resulting - 15 - in eventual total AC power loss. On the contrary, the 180-degree heading on the AC-powered course line indicator tends to confirm such ar. emergency.
This heading is incompatible with either the last established airway er the impact heading. Apparently AC power was available to the compass after the gyro horizons had failed and the aircraft was upset, bu~ was interrupted prior to impact. Additionally, several operators have reported that AC electrical failures were caused by malfunctions in the vertisyn or directisyn systems.
2.2 Conclusions (a) Findings l. The aircraft was airworthy and the crew properly certificated for the flight.
2. The gross weight anq e.g. were within allowable li~its.
3. The crew experienced a loss of primary attitude reference (both gyro horizons).
4. An upset occurred as a result of inade~uate attitude reference
while flyin.g under instrument flight conditions ir. turbulence.
5. The •Board is unable to establish the source of the electrical d:i.fficult;i;.
(b) Probable Cause The Board determines that the probable cause of this accident was the loss of control of the aircraft, in turbulent, instrument conditions, which could have been caused by a failure of both gyro horizons.
- 16 - 3. RECOMMENDATIONS The Board believes that various modifications which have been accomplished in the instrumentation and electrical systems of the aircraft since this acci- dent negate the requirement for additional recommendations at this time. Among the improvements was the installation of an attitude indicator powered by a source separate from the aircraft primary electrical system.
BY THE NATIONAL TRANSPOR Member II060