Accident Overview
On April 25, 2013, at approximately 1806 central daylight time, a Beech 35-C33A, registration N2713T, was substantially damaged during a forced landing following a loss of engine power near Knoxville, Tennessee. The commercial pilot sustained serious injuries. The airplane was registered to a private individual and operated under 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the post-maintenance test flight. The flight departed from Downtown Island Airport (DKX), Tennessee, at 1756.
Pre-Accident Maintenance and Pilot Actions
According to mechanics at a repair facility that had just completed work on the engine, the airplane owner had reported engine roughness and a fuel pressure fluctuation at 7,500 feet. He reported that turning on the auxiliary fuel pump smoothed the engine operation, and he continued the flight without further incident. The mechanics subsequently checked the fuel screens and fuel system components. They performed an extensive ground run-up and, after satisfactory results, flew the airplane to another facility for further inspection. During that inspection, they checked the ignition system, cleaned and gapped all spark plugs, tested spark plug wires, and checked all fuel screens, finding no abnormalities. A suction test from the firewall fuel fitting showed no bubbles indicating air leaks after 5 gallons of fuel flow on either tank selection. All fuel tank vents were clear. All engine compartment fuel hoses were cleaned and examined without anomalies. The engine-driven fuel pump inlet fitting was found loose; it was removed, cleaned, and reinstalled. Fuel flow was tested with the boost pump at the firewall and fuel divider, showing good uninterrupted flow. The fuel strainer was debris-free. All fittings were reconnected, and the system was pressure tested with no leaks. Several full-power run-ups were satisfactory, and screens were clean afterward. All performance parameters were normal.
The Accident Flight
The accident pilot, who was also a mechanic, performed a post-maintenance test flight. He conducted a preflight inspection and a full power run-up with the auxiliary fuel pump on and off, checking all systems; no anomalies were noted, and all systems checked satisfactorily. Takeoff power, fuel flow, and ground roll were normal. As a precaution, he turned on the auxiliary fuel pump before takeoff, and fuel flow was steady in the green arc. Shortly after rotation, the engine began to shudder, and fuel pressure dropped. During climb, approximately 100-200 feet above ground level, the engine lost about 70-80% of power and then lost all power. The pilot cycled the auxiliary fuel pump and mixture, with no change. He noted that he could not confirm total power loss because the propeller may have been idling at 600-800 rpm with a full power setting. The airplane could not maintain lift, and a forced landing was executed.
Post-Accident Examination and Engine Testing
According to a Federal Aviation Administration inspector, the airplane came to rest in a field in a residential area with substantial damage. The right wing outboard leading edge was buckled aft. The engine was separated from the firewall and engine mounts. The engine was removed and sent to Continental Motors Incorporated under NTSB oversight. Prior to test running, impact damage was noted, and minor parts were replaced. During testing, the engine started immediately on the first attempt and ran for 10 minutes before suddenly losing power, attributed to distortion at the throttle body from impact damage. Fuel flow to and from the fuel manifold was confirmed. The engine was restarted, a magneto check performed, and it ran at full power for about 20 minutes without abnormalities. After cooling and restarting, another test run showed no abnormalities. The magnetos were bench tested and partially disassembled with no discrepancies.
Operational Procedures
A review of the pilot operating handbook and pilot's abbreviated checklist revealed that the published procedures and limitations stated: prior to takeoff, the auxiliary fuel pump should be turned off for takeoff. The airplane was also placarded stating that "AUX FUEL PUMP OPERATION" for takeoff and landings should be in the off position except in case of loss of fuel pressure.