Page:CAB Accident Report, West Coast Airlines Flight 703.pdf/4

 The cockpit and cabin conditioning mixing valve was found set at one-third open to cabin heater air and two-thirds open to cabin blower air. The cabin heater assembly was tested for combustion product leakage by applying 5  p.s.i. pressure to the chamber with the inlet and exhaust ports blocked. Leakage caused the initial air pressure to drop to zero in 10 seconds. Further tests of this cabin heater assembly were conducted at West Coast Airlines' maintenance base at Seattle, Washington, and the at Columbus, Ohio. These tests showed the major leak to be at a crack where the crossover passage was welded to the combustion chamber. The heater was operationally tested following replacement of the igniters, and air samples taken at this time showed no evidence of carbon monoxide in the ventilating airstream.

The instrument flight shield (hood) was found fastened in place before the left windshield. The smoke mask for the pilot occupying the left seat was missing from its normally stowed position and was not recovered. The smoke mask for the pilot occupying the right seat was in its normally stowed position. The microphone on the left was unplugged but still hanging on its hook, and its male jack fitting was badly corroded. The landing gear control handle was down with the gates locked. The gust lock handle was in the off position. The left altimeter had a setting of 30.04 and indicated 2,345 feet; the right altimeter had a setting of 30.22 and indicated 580 feet. The left clock was stopped at 2·53, the right at 2:53. The company's policy required the clocks to be set on Pacific Standard time. The right fuel quantity indicator read 1,290 pounds, while the left indicator read 1,400 pounds. This aircraft was not equipped with an autopllot.

All of the aircraft's maintenance records were reviewed. The records indicated only routine maintenance during the six months period prior to the accident. All discrepancies in the aircraft's flight log, which was recovered from the wreckage, were noted as having been corrected. No satisfactory explanation can be given for the difference between the two altimeter settings.

The flight recorder with its tape was recovered undamaged from the wreckage and the tape was read by Board personnel. The recorder on the WCA F-27 aircraft derives its electrical power from 28-volt direct current and 115-volt alternating current, single phase. The recorder is automatically actuated when flat pitch (ground line) is terminated and, conversely, turned off when flat pitch is selected. The circuitry responds to the propeller buzzer cut-out relay and controls AC power to the flight recorder. The tape Indicated that this recorder operated continuously during the entire flight.

Examination of the tape traces during the final 127 seconds prior to impact established the following: Flight 703 started a descent from 7,498 feet m.s.l., 127 seconds prior to impact, and continued this descent to the lake's surface which is 4,180 feet m.s.l. The average rate of descent was 1,566 feet per minute. The airspeed varied between 102 and 113 knots, with an average of 107.8 knots. The magnetic heading varied between 269 degrees and 278 degrees. The vertical acceleration was almost constant at .95 g., with some variations between 1.1 g. and .8. The flight recorder tape revealed no evidence of an attempted flareout just prior to impact. (See Attachment A.)