Accident Overview
On August 7, 2012, at approximately 1620 central daylight time, a Williams T-51 Mustang airplane, registration N151TA, performed a forced landing at Wittman Regional Airport (KOSH) in Oshkosh, Wisconsin. The commercial pilot sustained serious injuries, and the airplane was substantially damaged. The aircraft was registered to and operated by a private individual under 14 Code of Federal Regulations Part 91 as a test flight. Visual meteorological conditions prevailed, and no visual flight rules flight plan was filed. The flight was local and originating at the time of the accident.
Pilot's Account
According to the pilot, the test flight aimed to troubleshoot lower engine power and higher-than-expected operating temperatures noted during a previous test flight. After takeoff, the airplane did not perform as expected, and the engine was slowly losing power. The pilot observed a coolant temperature of 225 degrees Fahrenheit while the airplane was only 250 to 300 feet above ground level. The pilot communicated with air traffic control about his intention to return to the airport and initiated a turn. During the turn, the pilot heard and felt an explosion behind him and a burning sensation on his back. All forward visibility was lost as the windscreen became black with smoke, although he could see a small amount out the left side.
Despite the pain from the burning sensation on his left side and limited visibility, the pilot continued to fly the airplane. He extended the landing gear and conducted a forced landing in the grass, just short of the general aviation ramp.
Post-Accident Examination
A Federal Aviation Administration (FAA) inspector who visited the accident scene reported that the right main landing gear collapsed during the forced landing. The airplane continued an additional 300 feet before coming to rest. The left wing and left flap sustained wrinkling during the landing.
The aircraft was recovered and moved to the owner's hangar in Ohio for further examination. The FAA inspector overseeing the examination noted no negative properties or operational failures during testing of the cooling system. The number four spark plug was severely damaged. According to the pilot, examination of the engine revealed no additional anomalies. The pilot added that a cooling hose had separated from the radiator, which was located behind him. The radiator and cooling lines had not been boxed in, meaning the cooling system was not isolated from the cockpit.
Previous Issues
Several days before the accident flight, the engine and cooling system had operated at higher-than-normal power settings and coolant temperatures. After that flight, the coolant temperature reached the maximum range of 250 degrees Fahrenheit, and coolant purged itself from the system. On a subsequent flight, the coolant temperature gauge malfunctioned, and shortly after takeoff, the pilot observed smoke in the cockpit. As he returned to the airport to land, he noted high engine oil temperature and low oil pressure. Examination revealed an oil leak between the cylinder head and engine block. Following that flight, a replacement engine was installed, but the cooling system was not replaced.