Final Report: Thelma and Louise' maneuver cited in helicopter crash

AINonline
July 25, 2007, 5:52 AM

Eurocopter AS 350-B2, Meadview, Ariz., Aug. 10, 2001–The crash of Eurocopter N169PA during an uncontrolled descent in precipitous terrain about four miles east of Meadview was caused by “the pilot’s in-flight decision to maneuver the helicopter in a flight regime, and in a high density-altitude environment, in which the aircraft’s performance capability was marginal, resulting in a high rate of descent from which recovery was not possible,” said the NTSB. “Factors contributing to the accident were high density altitude and the pilot’s decision to maneuver the helicopter in proximity to precipitous terrain, which effectively limited any remedial options available.”

The helicopter was operated by Papillon Airways as a Part 135 air-tour flight. It left the company base at Las Vegas McCarran International Airport (LAS) to tour the west Grand Canyon area, with lunch and refueling stops. The helicopter was en route back to LAS when the accident occurred. The helicopter was destroyed and the pilot and five passengers were killed; a surviving passenger sustained serious injuries. VMC prevailed, and a VFR flight plan was filed.

The surviving passenger was the only witness. She and the other passengers had worn headsets to hear the pilot’s tour commentary and announcements. She did not hear any bells or horns before the accident, no warning from the pilot or any Mayday radio transmission. Everything “went quiet, the blades stopped turning and we fell.”

The main wreckage, contained in an area approximately 40 feet in diameter, was located about a quarter mile west of, and 1,800 feet msl below, the rim of the Grand Wash Cliffs. Site elevation was 4,041 feet msl. The terrain slope was estimated to be 40 degrees.

Examination of the engine found indications of normal operation at impact, and no evidence of preimpact failure. The helicopter’s gross weight was estimated to be about 4,515 pounds, with the center of gravity within the longitudinal and lateral limits for this weight.

According to Eurocopter’s analysis, the helicopter would have had only a marginal capability to slow to zero airspeed at the ridgeline elevation, and if the helicopter was in a vertical descent of greater than 421 fpm, insufficient power was available to arrest the rate of descent.

Passengers on a tour with the pilot about a month before the accident said he was talking all the time. At one point, he turned his head toward the back and was talking to the passengers as the helicopter flew toward a cliff. The passengers were trying to point out that he was flying toward a cliff, but he pretended he did not understand. One witness said she finally picked up the microphone and said, “They are really scared…turn around and pull up the helicopter,” and he did. She could not estimate how far they were from the cliff when the pilot terminated the maneuver.

The pilot pointed out the cliff was used in the film Thelma and Louise, and later asked if they wanted to know what it was like to drive a car off a cliff. Despite their all saying “no,” he proceeded to fly very fast toward the edge of the cliff and then dove the helicopter as it passed the edge.

A video provided by one of the passengers showed a view of the helicopter flying at an estimated 100 feet over Grand Wash Cliff plateau. Just past the cliff edge, the pilot initiated a dive, with about 10 degrees nose-down pitch. Observations of the sound change in the engine and rotor noise were consistent with a lowering of the collective and unloading of the rotor system during this maneuver. Tour pilots nicknamed this maneuver the Thelma and Louise descent.

Evidently, the accident pilot preferred to cross the cliff edge at low altitude and high speed. He would then enter a rapid descent by lowering the collective and nosing the helicopter over into a dive. The evidence of a compact crash site located at the base of the cliffs is consistent with a maneuver of this type in which the descent was not arrested.

Analysis of the site indicates that there was insignificant forward velocity and a very high vertical descent rate at impact. Ground scar evidence clearly establishes that the helicopter was not rotating or spinning and, thus, was under positive pilot directional control, which establishes that the tail rotor and yaw control system were fully functional.

The extremely hazardous nature of the accident-site topography makes it improbable that the pilot elected to land in response to any emergency, particularly when several other adequate locations would have been available. The investigation also could not determine why the helicopter arrived at the accident site location at a high rate of descent, apparently fully functioning with a running engine and driving rotor system.

A probable scenario involves the pilot’s decision to maneuver the helicopter in a flight regime, and at a high density altitude, that significantly decreased its performance capability, resulting in a high rate of descent from which the pilot was unable to recover before hitting the ground. Additionally, the high rate of descent occurred in proximity to precipitous terrain, which effectively limited any remedial options available.

The NTSB said there was no evidence of any meteorological phenomenon that contributed to the accident other than the high ambient temperatures and resultant high density altitude.

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