Page:CAB Accident Report, West Coast Airlines Flight 703.pdf/5

 Flight tests were conducted in another F-27 aircraft with landing gear and wing flaps down, with a gross weight approximating that of N 2703 at the time of the accident. Two descents were made at an airspeed of 109 knots and a rate of descent of 1,580 feet per minute. To maintain this rate of descent and airspeed, 30 p.s.i. torque pressure on each engine was required. This power setting resulted in approximately 10,500 r.p.m. on each engine, and a deck angle of 9 degrees nosedown.

West Coast Airlines' Flight Training Manual requires that a satisfactory simulated emergency descent be demonstrated on type rating checks. The simulated emergency descent maneuver is performed as follows. The check pilot tells the trainee pilot to make such a descent, whereupon the latter passes control of the aircraft to the check pilot. The check pilot reduces power to idle and lowers the landing gears and flaps. Meanwhile, the trainee pilot dons his smoke (oxygen) mask and turns on 100 percent oxygen, unplugs his hand microphone, plugs in his smoke mask microphone and establishes communication. He then resumes control of the aircraft and establishes an airspeed of 129 knots which results in a rate of descent of about 2,700 feet per minute. The maneuver is to be terminated by the check pilot as soon as practicable after a satisfactory rate of descent is established. The WCA Flight Training Manual does not specify either an entering or a terminating altitude for this maneuver.

The Board concludes that the maneuver being attempted at the time of the accident was a simulated emergency descent. This belief is based on witness statements and physical evidence. A simulated emergency descent was one of the prescribed manuevers to be performed during the subject flight. Correlation of witness statements with traces on the flight recorder tape revealed that this maneuver had not been performed prior to the final descent. The extended landing gear, the fully extended wing flaps, the missing left smoke mask, the unplugged lefthand microphone, the throttle controls, the low shaft horsepower on both engines, and the instrument flight shield being in use are all compatible with a simulated emergency descent. The tape of the flight recorder manifested a relatively uniform, but unexplained, airspeed and a rate of descent markedly less than that prescribed for a simulated emergency descent. Examination of the tape traces, particularly of the heading trace which showed slight and continuous corrections to a 270-degree heading, coupled with the fact that the aircraft was not equipped with an automatic pilot can only mean that the aircraft was being controlled up to the moment of water impact.

The possibility of a defective or malfunctioning control system was considered. However, examination of the entire system revealed no evidence of any jamming or binding of any control. The operational integrity and continuity of all control systems at the time of impact, was established. The aircraft structure manifested no failure prior to impact and there was no evidence of inflight fire, collision with any foreign object, internal explosion or decompression.

Engine and/or propeller malfunctioning was also evaluated as a possible causal factor. Flight tests conducted subsequent to this accident clearly showed that the aircraft would have had to have some power on at least one of the engines, in order to maintain the airspeed and rate of descent indicated on the flight recorder tape. However, both engines exhibited evidence of low rotational speeds, with correspondingly low shaft horsepower, at impact. Also, engine controls and propeller blade pitch angles were found in positions compatible with normal low engine power. There was no sign of operational distress in either engine or in the propellers. Therefore,