Mechanical Failure Traced To An 'Incomplete Weld' On The Left Propeller Shaft

Pilot error following a mechanical failure is the probable cause of an accident involving a replica Wright B Flyer which occurred in Springfield, OH, in July, 2011. The accident resulted in the fatal injury of the two pilots on board the airplane for the test flight.

According to the operator’s accident report:

"The experimental airplane was involved in the initial phases of flight testing. Flying qualities, stability and control and performance were  being tested. Depending on the weather conditions test points were selected from a flight test matrix. The pilots, always two in the aircraft, would brief the flight, fly the test points and document the results.

"Depending on how well the test conditions were met the pilots would show that test point as complete and select another test to fly. The morning of the accident the pilots brief was not attended by any other person; exactly what points they were testing is not known."

NTSB Identification: CEN11FA528
14 CFR Part 91: General Aviation
Accident occurred Saturday, July 30, 2011 in Springfield, OH
Probable Cause Approval Date: 01/15/2013
Aircraft: WRIGHT B FLYER INC WRIGHT B FLYER, registration: N453WB
Injuries: 2 Fatal.

The experimental amateur-built replica airplane was on a test flight with two pilot-rated occupants. Another pilot heard a radio transmission from the accident airplane indicating that they were going to land in a field about 5 miles north of the departure airport. Witnesses reported that the airplane’s engine rpm varied while it was flying at a low altitude. The airplane was then observed in a spiraling descent to the ground. Postaccident examination of the airplane’s left propeller shaft revealed a broken weld, which would have prevented the left propeller from being driven by the engine. Further examination of the joint identified incomplete weld penetration during welding, thus about 25 to 35 percent of the through thickness of the propeller shaft tube was not welded to the propeller shaft end. This incomplete weld penetration occurred in the inner areas of the joint. Visible defects, such as pores and voids, were observed in the welded areas. The part’s engineering drawing specifies complete weld penetration. The on-scene accident examination of the wreckage did not reveal any other preimpact anomalies. Despite the resultant partial loss of thrust, the flight crew should have been able to maintain control of the airplane during the forced landing attempt.

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

The flight crew’s failure to maintain airplane control following a partial loss of engine thrust during cruise flight. Contributing to the accident was the failed weld as a result of incomplete welding on the left propeller shaft, which led to the partial loss of engine thrust.

(Wright B Flyer replica pictured in file photo)

FMI: www.ntsb.gov