Two passengers seated in the rear of a ski-equipped Cessna 185F SURVIVED a fall of about 3,500 feet after the aircraft broke up in mid-air near Sept-Iles, Quebec on 17 February 1997. The pilot and aircraft owner were seated in the front seats and were fatally injured. (PICTURE)
The rear passengers reported that, while in flight at cruise altitude of about 4,500 feet asl or 3,500 feet agl, they suddenly noticed that their legs were hanging in the air and they were descending in a turn.The fuselage had separated between the front and the rear seats, and the engine had broken away. They tried to unfasten their seat belts, but centrifugal force prevented them from doing so. The forward fuselage had struck the snow-covered surface upside-down, penetrated through five to six feet of unpacked snow, and struck the ground. The rear of the fuselage struck the ground on the left side. The passenger seated on the right was not injured, and he made a fire to protect his companion from the cold and keep them both alive. Although the left passenger could not move around, he was able to call for help on his cellular phone one hour after the occurrence. About three hours later, they were rescued and transported to hospital for the usual examinations.
The TSB (Transport Safety Board) determined that an incorrectly tightened bolt and non-compliance with an airworthiness directive allowed the right ski and landing gear to separate from the aircraft in flight and strike the right wing. The aircraft subsequently broke up and fell to the ground in pieces.
The Airglas skis on the aircraft were subject to a mandatory Service Bulletin requiring modifications to prevent the skis from rotating downwards, which causes severe unbalancing of the aircraft and makes it hard to control. The bungees were to be replaced with a type that was more suitable for low temperatures. The bungee and forward steel cable attachments were to be relocated on the skis. As well, with the skis installed, the aircraft speed was to be limited to 160 KIAS, and a speed limit placard was to be installed on the instrument panel. The SB was subsequently superseded by an airworthiness directive (AD) which in Canada, limited the aircraft to 145 KIAS when the skis were installed. That AD had not been completed on the accident aircraft. (PICTURE)
BREAK-UP SEQUENCE
At cruise altitude, as the aircraft speed increased, the angle of attack decreased and the right ski rotated downward. It is possible this situation was aggravated because one nut was not tight enough, and the right ski was hanging lower than the left ski.The sudden increase in resistance when the ski rotated downward would have caused the aircraft to pitch down. The bungee stretched, probably resisted for a few seconds allowing the pilot to attempt to correct the attitude, then failed.
When the bungee failed, it allowed the ski to continue rotating. The bolts holding the metal plate on the ski tip failed in tension, allowing the steel cable to recoil and strike the propeller. The propeller plane of rotation was modified, this produced excessive tension on the engine mount brackets, which failed, and the engine separated from the aircraft. (PICTURE)
When the engine separated, the aircraft pitched up as a result of aerodynamic forces and the shift of its center of gravity. The ski then cut the right wing strut and the leading edge aft to the main spar. During this sequence, the forward carry-through structure was damaged, allowing the two wings to tear off. Finally, lacking a viable structure, the fuselage separated at the aft door pillar. Transfers of color from the ski were also found on the vertical stabilizer and left elevator, suggesting that the fuselage rotated to the right after losing the right wing.
ACKNOWLEDGEMENT
This article was reprinted from "REFLEXIONS", a Transport Safety Board of Canada publication.
This C130 was delivering supplies and scientists to the South Pole. It normally does a few touch and go's on the snow to test the surface and to expose any possible crevasses. The Herc had completed one touch and go, (you can see the ski tracks in the top of this photo), when for some reason the pilots elected to make it a full stop. The snow could have been too deep to complete a touch and go. The aircraft taxied and dumped some of its cargo to lighten its load. The Herc's left ski entered a crevasse. You can see the crevasses in the 4 photos.
The first and second pictures show the C130's left gear (ski) in the crevasse.
You can see where the crew dumped some cargo out in the top of this photo.
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