PADUCAH, KY, USA
N72DE
Ekstrom-Farrington TWINSTAR
The gyroplane was on short final, about 15 feet above the ground, when it went into an uncommanded right turn and right roll. The heading changed 180 degrees, and the gyroplane impacted sod near the runway threshold. The gyroplane had a rotor brake mechanism which was activated by pushing the cyclic control full forward. A through-bolt which had attached the two lateral control arms to the yoke assembly, was discovered missing, and the right lateral control arm had separated from the yoke assembly. The kit manufacturer was considering implementing a clamp-type rotor brake system, much like a bicycle's, to prevent rotor brake forces from passing through the flight control system.
On August 25, 1998, about 1600 Central Daylight Time, a homebuilt Twinstar gyroplane, N72DE, was substantially damaged during landing at Farrington Airpark (FIO), Paducah, Kentucky. The certificated private pilot was uninjured, and visual meteorological conditions prevailed at the time of the accident. No flight plan was filed for the local instructional flight, conducted under 14 CFR Part 91. According to the pilot, the gyroplane was on short final, about 15 feet above the ground, when it went into an uncommanded right turn and right roll. The heading changed 180 degrees, and the gyroplane impacted sod near the runway threshold. A Federal Aviation Administration (FAA) Inspector examined the wreckage. He reported that a through-bolt (AN type), which had attached the two lateral control arms to the yoke assembly, was missing, and that the right lateral control arm had separated from the yoke assembly. Additionally, no maintenance work had been performed just prior to the accident. The inspector also noted that the gyroplane had a rotor brake mechanism which was activated by pushing the cyclic control full forward. The president of the company that owned the accident gyroplane, as well as manufactured the Twinstar kits, stated that the missing bolt could not be found. He also checked the rotor system after the accident, and noted no blade damage that might have been caused by a bolt passing through it. He said that the bolt may have failed through repetitive use of the rotor brake over a long period of time, or through one heavy application of the rotor brake. He felt that normal use of the rotor brake should have produced less stress on the bolt than would normal flight operations. He also noted that the rotor head had been off and on several times, and raised the possibility that the bolt could have been overtorqued. The president stated that he sent an advisory to other kit owners to check the bolts, and that he was considering implementing a clamp-type rotor brake system, much like a bicycle's, to prevent rotor brake forces from going through the flight control system.
Failure of a through-bolt that attached the lateral control arms to the yoke assembly, due to unanticipated rotor brake forces through the flight control system.
Source: NTSB Aviation Accident Database
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