NTSB Identification: LAX97LA061 .
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14 CFR Part 91: General Aviation
Accident occurred Thursday, November
21, 1996 in FLAGSTAFF, AZ
Probable Cause Approval Date: 2/2/1998
Aircraft:
McDonnell Douglas MD-600N, registration: N630N
Injuries: 1
Uninjured.

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 as follows:
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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