Page:CAB Accident Report, Flying Tiger Line Flight 282.pdf/11

 An analysis of available meteorological information indicates that, at the time of the accident, Sweeney's Ridge would have been obscured by clouds and light rain. Winds would have been from the west-southwest at 30 to 35 knots, with occasional gusts to 45 knots. This would have created moderate to severe turbulence and a marked downdraft condition in the lee of Sweeney's Ridge. Turbulence would have been encountered throughout the flightpath, increasing in intensity as the flight approached the ridge.

The ATC clearance and routing provided was in accordance with the crew's request and all ground electronic navigational aids were operating satisfactorily. The Gap homer and the Outer Marker compass locator frequencies were selected on the aircraft's ADF receivers and the loop bearing of the No. 2 ADF system validates electrical power at impact. Even assuming a malfunction of the aircraft's VOR course deviation needle, adequate guidance to a safe altitude was possible from the localizer course, the outer compass locator of the instrument landing system or the Gap low frequency homer. Also, three separate sources of heading information were available.

The phraseology "Radar Contact" is used when radar identification of an aircraft is established. This term, as presently defined, indicates that the air traffic controller has identified the aircraft on the radar display and that radar service in the form of radar separation, radar navigational guidance, or radar monitoring can be provided within the limitations of the facility. Critical obstruction clearance criteria for the Runway 28 departure at San Francisco, and limitations of the facility radar equipment, precluded radar vectoring service until the aircraft reached 1,500 feet. If the foregoing limitations were unknown to the crew, they may have believed the aircraft was under continuous radar surveillance from the time departure control reported radar contact. The crew may have disregarded their instruments believing their flight was monitored by the radar controller and, because of the turbulent weather conditions encountered, they may have concentrated their efforts on maintaining control of the aircraft. In those circumstances, the crew may have failed to detect errors in the instrument presentation to the extent that there were in fact erroneous indications portrayed.

It is possible that a contamined switch could cause intermittent large errors in navigational information displayed on the pilot's instrument. A review of log discrepancies on a number of L-1049 aircraft presently owned and flown by the Flying Tiger Line revealed navigation errors in the VOR system that may have been caused by contamination of the radio relay switch, even though the VOR navigation selections had been properly made.

Flight 282 made a left turn of approximately 55 degrees shortly after takeoff. The reconstructed flightpath indicates that this heading was maintained until impact. Since the relay switched in N6915C were destroyed by fire, it was impossible to determine whether contamination existed. However, the radio transmission before impact indicates the copilot's concern about the position of the aircraft. The turn after takeoff and the subsequent concern of the copilot could be attributed to a malfunctioning VOR since it is the prime navigation aid. The straight track flown after the turn indicates that the pilot was using at least some of the aircraft's navigation instruments for guidance.