NTSB Identification: FTW00LA042.
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Accident occurred Sunday, December 12, 1999 in STERLING CITY, TX
Probable Cause Approval Date: 03/02/2001
Aircraft: King LANCAIR 235/320, registration: N717SK
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.

During descent, the propeller separated from the experimental airplane. The pilot initiated a forced landing to a county road, and during the approach, the left main landing gear 'struck the bottom wire of a two wire service line,' which crossed over the road. The airplane 'stalled,' yawed 20 degrees to the left, and 'hit the middle of the road on all three [landing] gear.' It then headed off the left shoulder of the road where the right wing hit a road sign, shearing off the outboard 4 feet of the wing. The propeller system was not recovered. Examination of four of the six propeller attaching bolts revealed that they failed as a result of fatigue. The shank of one of the bolts, in the area located immediately adjacent to the fracture face had been subjected to 'extensive rubbing damage.' Two of the submitted bolt pieces contained washers. Examination showed that both washers were permanently deformed into dish shapes and were galled by rubbing. Rubbing and galling damage was also found on contact surfaces of the self locking nuts on all four bolts. The 3-bladed wooden experimental propeller had 47.4 hours since installation. The combination of low time since installation and rubbing damage on the bolts indicates the application of inadequate pre-stress (low torque) during propeller installation.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The fatigue fracture of the propeller attaching bolts, due to improper torque during the installation of the propeller by other maintenance personnel. A factor was the lack of suitable terrain for the forced landing.

Full narrative available

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