Primary finding
Probable cause
The pilot's improper planning/decision, and failure to verify the airplane's performance data. The airplane's lack of climb capability with the newly manufactured propeller was a related factor.
Investigator assessment
Analysis narrative
The pilot had manufactured a new propeller for his airplane. Before taking off on the first flight after certification, he performed taxi and runup tests on the engine and airplane. After takeoff, the airplane did not climb very fast and reached an altitude of only about 50 feet. After realizing that the airplane was not performing as expected, he attempted to stay over a clear field. To do this, he had to make a shallow turn, and the airplane started to descend. The airplane then struck trees at approximately 3,500 feet from the departure end of the runway. A postaccident investigation revealed no evidence of mechanical failure of the engine. When questioned, the pilot said that he expected the new propeller to produce 110 horsepower at 4500 rpm or 65 horsepower at 3000 rpm. However, during takeoff, the rpm only reached about 2600 rpm.
Source record
Factual narrative
On December 12, 1995, about 1625 central standard time, N823GM, a McKibben GN-1 Aircamper operated by a private owner as a 14 CFR part 91 personal flight, crashed in Mayhew, Mississippi. Visual meteorological conditions prevailed at the time and no flight plan was filed. The airplane was substantially damaged and the private pilot was not injured. The flight was originating at the time of the accident. The pilot stated that before to the accident he had performed 10 hours of taxi and runup tests. He had decided on the type of propeller by the designer's suggestions and he manufactured the propeller himself. He stated that his horsepower ratings were at 4,500 rpm it should be 110 horsepower and at 3,000 rpm it should be 65 horsepower. The pilot performed static runups on the engine and it came up to 2,500 rpm. During takeoff the aircraft did not accelerate as rapidly as he would have expected. The airplane did not climb very fast and reached an altitude of approximately 50 feet. After realizing the airplane was not performing as it was to be expected he attempted to stay over a clear field. To do this he had to make a shallow turn and the airplane started to descend. The airplane then struck trees about 3,500 feet from the departure end of runway 18. A post-accident investigation revealed that there was automotive fuel in the fuel tanks, fuel lines, filter, and the carburetor. There was no evidence of mechanical failure of the engine. There has been repeated requests to receive a written statement and pilot operator's report from the pilot but the pilot has ignored all requests. -