NTSB Identification: LAX97LA061.
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Accident occurred Thursday, November 21, 1996 in FLAGSTAFF, AZ
Probable Cause Approval Date: 02/02/1998
Aircraft: McDonnell Douglas MD-600N, registration: N630N
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The helicopter was being flight tested to validate certification criteria for height velocity curves at a maximum gross weight and zero airspeed at a high density altitude airport. On the fourth test profile, the pilot allowed the aircraft to descend below the target altitude of 800 feet agl by almost 70 feet. The ground test engineers observed the drift down and didn't advise the pilot because they assumed he had already begun the autorotation after he had made the 3 second call, and also they believed their ground equipment was inaccurate. The pilot delayed the autorotation for about 8 to 12 seconds and then lowered the collective. The aircraft landed hard exceeding the maximum load for the landing gear system. The horizontal speed at touchdown was 52 knots instead of the target speed of 65 knots. The test helicopter was equipped with standard analog altimeters with pointers that have a lag time instead of the more accurate real time digital altimeters.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's inattention to the altitude and inadvertent late entry into an autorotation maneuver below the established minimum test altitude with a helicopter operating at maximum gross weight in a high density altitude environment that led to a subsequent hard landing. Contributing were the lack of positive communications between ground test personnel and the pilot regarding the low altitude, and the lack of accurate in-flight and ground altimeter equipment. Full narrative available
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