History of Flight
On July 21, 2012, at approximately 0830 central daylight time, a Mooney M20E airplane, registration N1310W, was substantially damaged during a forced landing following a loss of engine power. The pilot was diverting to Marked Tree Municipal Airport (6M8) in Marked Tree, Arkansas, and was on approach to runway 36 when the forced landing occurred. The pilot sustained minor injuries; the passenger was uninjured. The airplane was registered to and operated by the pilot under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and the flight operated on an instrument flight rules flight plan. The flight originated from West Memphis Airport (AWM) in West Memphis, Arkansas, at about 0804, with an intended destination of Sullivan Regional Airport (UUV) in Sullivan, Missouri.
The pilot reported that approximately 5 minutes after reaching a cruise altitude of 6,000 feet mean sea level, the engine began running rough with an accompanying partial loss of power. The engine exhaust temperatures on all four cylinders dropped from about 1,350 degrees Fahrenheit to below 1,000 degrees Fahrenheit. Other engine indications appeared normal. The pilot's attempts to resolve the issue were unsuccessful, leading him to divert to 6M8. As the flight approached the airport, the engine continued losing power. Unable to maintain a proper glide path to the runway and concerned about an inadvertent aerodynamic stall, the pilot executed a forced landing to a bean field short of the runway.
Pilot Information
The pilot held a private pilot certificate with single-engine land and instrument airplane ratings. He was issued a third-class airman medical certificate on June 25, 2012, with a restriction for corrective lenses. The pilot reported approximately 2,148 hours total flight time, with about 1,900 hours in Mooney M20E airplanes. His most recent flight review was completed on February 6, 2011.
Aircraft Information
The accident airplane was a 1963 Mooney M20E, serial number 198. It was a four-place, single-engine design with retractable tricycle landing gear, powered by a 200-horsepower Lycoming IO-360-A1A engine, serial number L-2994-51A. Maintenance records indicated the most recent annual inspection was completed on July 12, 2012, at a total airframe time of 5,137.19 hours. At that inspection, the engine had accumulated 1,907.19 hours since overhaul. No maintenance entries followed the annual inspection. The recording tachometer indicated 5,138.37 hours at the time of the accident.
Maintenance records showed repairs to the airplane fuel system in July 2010, including an overhaul of the fuel injection servo, with a tachometer reading of 5,024.9 hours at that time. The pilot reported no fuel system-related repairs since purchasing the airplane in March 1989, except occasional fuel injector cleaning.
Meteorological Information
Weather conditions recorded at West Memphis Airport (AWM), about 25 miles south of 6M8, at 0853, were: wind from 070 degrees at 6 knots, 10 miles visibility, clear sky, temperature 28 degrees Celsius, dew point 23 degrees Celsius, altimeter 29.98 inches of mercury.
Wreckage and Impact
The airplane remained upright and came to rest about 325 feet from the arrival end of runway 36. The landing gear separated from the airframe, and the right wing was substantially damaged. The cockpit and cabin remained intact.
A postaccident examination was conducted after recovery. The engine was removed from the airframe for recovery. Engine control continuity was intact prior to engine removal. Fuel samples showed no visible sediment or contamination, consistent with 100 low lead aviation fuel. Fuel flow was confirmed from each wing tank to the firewall fuel fitting. Electrical continuity from the cockpit ignition switch to firewall leads was confirmed.
The engine crankcase and cylinders appeared undamaged. Internal engine and accessory section continuity were confirmed via crankshaft rotation. The fuel flow divider appeared undamaged; fuel injector lines were intact, and nozzles were unobstructed. Spark plugs were unremarkable. Intake and exhaust systems appeared intact. No anomalies were observed with the engine-driven fuel pump except minor internal corrosion deposits. Both magnetos produced spark across all leads when tested. No anomalies consistent with a loss of available engine intake air were observed.
Tests and Research
Bench testing of the engine fuel injection servo revealed that the unit performed as expected at each test point. Fuel flow rates stabilized at each test point and approximated specifications for an in-service servo unit. However, variations in fuel flow rate were observed during testing, with a range inconsistent with normal servo function.
A teardown examination of the fuel servo revealed a missing section of an O-ring installed on the mixture control lever assembly. An O-ring fragment was located on the surface of the mixture control valve plate, measuring approximately 7 mm by 2 mm, which appeared to correspond to the size of the missing O-ring section. No other anomalies were observed in the fuel servo unit.