Federal investigators said today there are strong indications that Midwest Express Flight 105 stalled -- literally stopped flying -- before crashing here Friday even though the jetliner theoretically had enough engine power to continue flight. All 31 people aboard were killed.
It has been established that one of two engines stopped working before the crash immediately after takeoff, but that alone is not a fatal occurrence. Investigators are attempting to determine what the pilot did in reaction to the engine failure, but discount obvious pilot error in their early analysis, they said. The plane reached an altitude of 900 feet when the pilot radioed he had an emergency. The plane then rolled and dived, action consistent with a stall.
In a stall, air stops moving over the wings rapidly enough to keep the aircraft aloft. The cockpit voice recorder shows that the stall warning sounded shortly after takeoff. That warning -- which sounds somewhat like a rattlesnake ready to strike -- predicts the probability of stall in the absence of pilot action. The sound continues to the end of the tape, sources said.
However, the tape does not continue to the instant of impact, indicating a possible electrical failure shortly after the stall warning sounded. That adds credence to the theory that something catastrophic was going on in the rear of the aircraft.
Investigators are concentrating on the possibility that the engine failure was "uncontained," which means that parts of the engine broke away, possibly severing vital control cables.
The aircraft, a twin-engine McDonnell Douglas DC9, has redundant cable-driven control systems, assisted with hydraulic "power steering." Engineers familiar with the aircraft are having trouble envisioning flying engine parts cutting through the engine casing, the aircraft's fuselage and two sets of control cables.
National Transportation Safety Board Chairman Jim Burnett said investigators found more engine parts as they continued their search of the runway area. So far, he said, 20 engine compressor blades or parts of blades have been found along with a few pieces of the engine covering.
The compressor is the part of a jet engine where air is ingested, then compressed as it is sent to a combustion chamber to be mixed with fuel and ignited. The exhaust powers the airplane and turns a turbine, which drives the compressor. Compressor and turbine blades spin at high speeds. The engine is supposed to contain those blades if they break loose.
The engines on this plane are JT8Ds, manufactured by Pratt & Whitney, a division of United Technologies Corp.
The investigation was hampered today by 1.49 inches of rain, which turned the field where the plane crashed into a quagmire and postponed for perhaps a day or two any attempt to extricate the suspect engine from the wreckage.