Accident Overview
On September 15, 2017, at 1615 central daylight time, a Beech A36 airplane, registration N18403, collided with a hay bale during a forced landing following a loss of engine power while on approach to the McAlester Regional Airport (MLC), McAlester, Oklahoma. The private pilot, who was operating the flight under 14 Code of Federal Regulations Part 91 as a personal flight, sustained minor injuries. The airplane sustained substantial damage. Visual flight rules conditions existed near the accident site at the time of the accident.
Flight History
The flight departed from Garner Field Airport (UVA), Uvalde, Texas, at 1357. The pilot reported purchasing fuel prior to takeoff, with both main fuel tanks and both tip tanks full. For takeoff, the pilot selected the right fuel tank and used a stopwatch to switch fuel tanks every 25 minutes during the flight. Approximately 8 minutes after takeoff, while climbing through 5,000 ft, the pilot noticed fuel leaking from the left fuel tank filler cap for a short period. The remainder of the flight was uneventful until the pilot prepared to enter a downwind leg at MLC, at which point the engine lost power. The pilot switched fuel tanks and attempted to restart the engine without success.
Forced Landing and Damage
The pilot stated that during the off-airport forced landing, the aircraft touched down hard. Both main landing gear were pushed up through the wings, and the right wing contacted a hay bale. The left wing remained attached to the fuselage. The right tip tank separated from the right wing, which remained connected to the fuselage by control cables and wiring. The fuel system was compromised due to impact damage.
Postaccident Examination
A postaccident examination of the wreckage was conducted on October 24, 2017. Both wings were detached from the airframe and stored outdoors. Both fuel caps were removed, inspected, and found to have cracks in the main O-ring seal. The left fuel cap was tested in place by applying air pressure to the fuel outlet line and plugging the vent system and tip tank fuel inlet. A soap-and-water solution applied around the cap bubbled, indicating an air leak. Air could be felt escaping from around the fuel cap outer seal and the center seal. The right wing was not tested due to impact damage. The aircraft logbook showed that the fuel cap O-rings were replaced with new O-rings during the annual inspection on April 1, 2016.
The engine, which was not damaged, had been converted from an IO-520 per STC SE10746SC. A borescope examination of the piston domes, cylinder walls, and valve faces showed normal wear and combustion deposits. The propeller was damaged during the accident, precluding its use for an engine run; a slave propeller was installed. The top spark plugs appeared normal in wear and color and were reinstalled.
The airframe was secured on a flatbed trailer. An alternate fuel system was rigged to the left wing fuel inlet line at the fuselage. The fuel line going into the JPI fuel flow transducer was disconnected, power was applied, and the fuel system boost pump was turned on until positive fuel flow was verified at the disconnected line. The line was reconnected, and the engine started on the first attempt, idling between 600 and 700 rpm. The rpm was increased to 1,000 rpm, then to 1,500 rpm, and a magneto check showed a drop of 60 to 80 rpm per magneto. The engine run was limited to 1,500 rpm due to fuselage security on the trailer. The process was repeated with an alternate fuel supply to the right-wing fuel inlet line, with the same results. When the fuel selector was switched to the off position with the engine running at 1,500 rpm, the engine ran for about 25 seconds before stopping. The engine started and ran smoothly as tested up to 1,500 rpm.
The airplane was equipped with a JPI FS-450 that monitored fuel flow, fuel used, and fuel remaining. The unit was removed and sent to the National Transportation Vehicle Recorder Division for examination. The device stores the last remaining record of fuel used and fuel remaining in gallons, but does not indicate which fuel tank contains the remaining fuel. Upon powering the unit, the display showed 45.4 gallons of fuel used and 66.6 gallons of fuel remaining. These amounts do not account for the unknown quantity of fuel that leaked from the left fuel tank filler cap. The pilot reported that at 1524, both fuel tanks were indicating about three-quarters full.