Accident Summary
On April 3, 2021, at about 1248 eastern daylight time, a Mooney M20C, registration N2953L, sustained substantial damage in an accident near College Park, Maryland. The private pilot, who was the sole occupant, was not injured. The flight was operated under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot and Witness Accounts
The pilot stated that during preflight inspection he discovered water in the left fuel tank. He sampled the tank five times until no water was visible, then dried the collection tube and sampled twice more with clear results. He did not drain the selector valve sump drain. He selected the left fuel tank for takeoff and performed an engine run-up, noting only a discrepancy with the auxiliary fuel pump, which he left off. During takeoff, after rotating at 83 mph, the engine began to cough and sputter. He looked left but continued straight ahead; the next memory was the sound of ground contact. The airplane came to rest upright near the departure end of the runway.
A pilot-rated witness reported that the engine was running rough while still on the ground about halfway down the runway, with rapid power loss, surging, and then a nose-up elevator deflection after the abnormal engine sound.
Video Evidence
A video provided by the airport manager showed the airplane over the runway in a slight nose-up attitude, less than a wingspan high, with main landing gear extended. The airplane gained slight altitude, then began to descend. While at low altitude, the left wing dropped, and the airplane descended nose-low, with the left wing impacting the runway. The airplane rotated clockwise and came to rest upright.
Postaccident Examination
Examination revealed substantial damage to the left wing. From the left fuel tank, 8 ounces of water were drained. Water was detected in the flexible fuel hose from the firewall fitting to the engine-driven fuel pump inlet. Additionally, about 5 ounces of a fluid containing equal parts fuel and water were drained from the carburetor bowl.
An on-wing pressure check of the fuel caps, using a maintenance procedure for later models, showed large bubbles around the outer perimeter of the left fuel cap and small bubbles on the aft side of the right fuel cap near the lever. No bubbles were noted around the axle for either cap. The outer perimeter of both fuel tank access panels tested without leaks.
The fuel caps were sent to the manufacturer for testing. Both had loose handles with very little resistance and no audible snap when closed and locked. The left cap could not be tested due to extensive leakage; the right cap failed pressure testing. Disassembly revealed both contained unapproved, modified, or missing parts. After reassembly with new hardware, both passed acceptance testing, including pressure testing to 25 psig. Returned to the salvage facility for on-wing testing, both caps again leaked.
Further testing at the manufacturer involved each wing plate with its attached doubler, adapter, and fuel cap. Using a fixture, no leakage was noted between the fuel cap and adapter, but leakage occurred between the adapter and doubler of each assembly at low pressures (0.45 psi and 0.28 psi), increasing with pressure.
Maintenance History
Postaccident examination of the fuel tanks per Mooney Service Bulletin M20-230 revealed no anomalies; all drain holes were open and fuel tank drain valves were correct, with no capability for trapped water.
Airworthiness Directive (AD) 85-24-03, effective January 6, 1986, required inspection of fuel tank bays and ribs, and a visual inspection of fuel caps per Mooney Service Bulletin (SB) M20-229 (dated February 12, 1986). SB M20-229A later specified pressure testing by applying 0.5 psi to the fuel vent line and checking for leaks around the cap.
The mechanic who performed the airplane's last annual inspection in July 2020 stated he complied with AD 85-24-03 by applying window cleaning solution to the wing around the fuel caps and blowing into the vent tube by mouth pressure, observing no bubbles.
One co-owner reported that on February 4, 2021, he and the other co-owner replaced the o-rings of each fuel cap due to water in the fuel tanks. This action seemed to diminish water infiltration during rain. Additionally, wing covers were used when the airplane was on the ramp, but these were off when the pilot arrived. The mechanic was not contacted about the water issues.