FALL RIVER, MA, USA
N8447
LACH BENSEN B-8M
AS THE PILOT WAS FLARING TO LAND, THE ROTOR CONTROL ARM (CONTROL STICK) FAILED AT A LOCATION JUST ABOVE THE PILOT'S HEAD. THE GYROCOPTER THEN ROLLED OVER AND CRASHED. A METALLURGICAL EXAMINATION REVEALED THE CONTROL ARM HAD FAILED FROM FATIGUE. THE FATIGUE ORIGINATED WHERE THE CONTROL ARM HAD BEEN CHAFED BY A LOOSE CLAMP.
On Thursday, September 2, 1993, at about 0830 EDT, a Lach Bensen B-8M, N8447, owned and operated by Walter Lach of Fall River, Massachusetts, rolled over and crashed during a landing at the Fall River Municipal Airport. The gyrocopter was substantially damaged. The pilot, who was the sole occupant, was seriously injured. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight was conducted in accordance with 14 CFR 91. The pilot reported that as he was flaring to land, the rotor control arm (control stick) failed. The gyrocopter then went out of control, the engine RPM began increasing, and the gyrocopter roller over and crashed. A post-accident examination of the gyrocopter revealed the control arm had failed in an area above the pilot's head. The fracture was 90 degrees to the longitudinal axis of the control arm. An examination of the rotor control arm revealed that it had been manufactured from unalloyed aluminum tubing. The tubing was about one inch in diameter with a wall thickness of about 1/16 inch. Hardness of the tubing averaged 84.2 HRF, which was consistent with unalloyed aluminum. Metallurgical examination of the rotor control arm revealed that it had failed from fatigue. Fatigue had originated in two areas on the outer diameter of the control arm, where it had been chafed by a loose clamp. Fatigue had progressed through the wall thickness of the control arm, then it continued circumferentially in both directions. The fatigue crack had progress about half way around the tube before final overstress failure occurred.
FATIGUE FAILURE OF THE GYROCOPTER'S MAIN ROTOR CONTROL ARM. fACTORS RELATED TO THE ACCIDENT WERE: A LOOSE CLAMP ON THE ROTOR CONTROL ARM, DUE TO INADEQUATE MAINTENANCE OR INSPECTION, WHICH RESULTED IN CHAFING OF THE CONTROL ARM.
Source: NTSB Aviation Accident Database
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