Inquiry into Grand Canyon helicopter crash cites loss of control in tight manoeuvre

A protracted and complex helicopter accident investigation has led the US National Transportation Safety Board (NTSB) to press the Federal Aviation Administration to mandate from 2007 cockpit image recording and 2h cockpit voice recorders to be installed in all new-build turbine aircraft carrying six or more passengers.

The investigation examined the 10 August 2001 Grand Canyon sightseeing flight by a Papillon Airways Eurocopter AS350-B2, which ended with a steep descent to impact, killing the pilot and five of the passengers. The one surviving passenger was seriously injured.

According to the NTSB report, there is no evidence to indicate a pre-impact mechanical malfunction. It says: "Given the density altitude, helicopter performance considerations, and virtually all of the signatures [evidence] at the [impact site] and in the wreckage...a probable scenario involves the pilot's decision to manoeuvre the helicopter in a flight regime, and in a high density-altitude environment, which significantly decreased the helicopter's performance capability."

This combination, says the NTSB, resulted in a high rate of descent from which the pilot was unable to recover before impact, partly because of the proximity to steep terrain, which "effectively limited remedial options available". No emergency call was heard by air traffic control or aircraft in the vicinity, and the surviving passenger - who was wearing a headset - told the NTSB that she "did not hear any bells or horns before the accident and did not hear a verbal warning from the pilot".

The NTSB's call for flight recorders came from the fact that the probable cause was, in the end, determined by the exhaustive process of eliminating alternative possibilities, as well as examination of the crash site and study of the conditions on the day. The inquiry found nothing to criticise as regards the pilot's ability, experience, training, state of mind, or the maintenance of the helicopter.

According to an NTSB analysis of secondary radar returns, the accident occurred soon after the helicopter had passed at low level over a ridge at the edge of the Grand Wash Cliffs, at which point pilots normally descend about 1,000ft (300m) to 4,500ft altitude, the correct separation height for the direction. Captured on video taken by previous Papillon passengers and seen by the NTSB, this can be done fairly vigorously and is nicknamed the "Thelma and Louise" manoeuvre after the film in which two women intentionally drive a car at speed over a Grand Canyon cliff.

Papillon Airways says that, as a party to the investigation, its preliminary conclusions "are not consistent with those of the NTSB".



Source: Flight International