Accident
On April 26, 2019, at about 1455 central daylight time, a Beechcraft E-50 airplane, registration N29Y, sustained substantial damage during an accident near Sheldon, Missouri. The commercial pilot was not injured. The airplane was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
Flight
The flight originated from El Dorado Springs Memorial Airport (87K), Missouri, destined for Atkinson Municipal Airport (PTS) in Pittsburg, Kansas. It was the airplane's first flight since an annual inspection completed that day. After climbing to about 3,000 ft above mean sea level, the pilot configured for cruise. Approximately ten minutes into the flight, the right engine began emitting sputtering noises and backfired. The pilot advanced the left engine throttle and observed a large, dark, mostly black smoke trail from the left engine about one minute later. At about 1,700 ft msl (800 ft agl), with both engines losing power, the pilot executed a forced landing to a tilled dirt field. He did not have time for an emergency shutdown. The main landing gear was extended; during the landing roll, the nose landing gear wheel collapsed, causing substantial fuselage damage. The nose and both propellers struck the dirt. The pilot egressed without further incident.
Aircraft Information
The airplane was a Beechcraft E-50. The pilot reported 70 gallons of 100 low lead fuel onboard; an FAA inspector later found about 60 gallons (30 in each main tank). Maintenance records showed no uncorrected discrepancies. The mechanic reported the annual inspection began in early March 2019; no major discrepancies were noted. During inspection, a small amount of water was found in the fuel sumps, described as typical. The right engine had a bad exhaust valve on one cylinder, which was replaced. Both engines were ground run at various power settings without noted discrepancies.
Postaccident Examination
Postaccident examination revealed difficulty manually manipulating the fuel tank selector and carburetor heat levers. The airplane lacked an outside air temperature gauge. Fuel samples from left and right side sumps showed no anomalies, but the left engine fuel strainer contained about one teaspoon of debris. Engine control cable continuity was established; both crankshafts rotated with drivetrain continuity. A hole was found at the exhaust valve seating point on left engine’s number 6 cylinder and right engine’s number 2 cylinder. Left engine’s number 4 cylinder had internal head damage, and its piston had a hole and damage. Both oil screens were full of debris. Spark plugs showed normal wear or oil fouling. The propeller governors contained small metal particles; the right side lacked a screen.
Laboratory Examination
Components submitted to the NTSB Materials Laboratory included the left engine’s number 4 piston and number 6 cylinder, the right engine’s number 2 cylinder, and both oil screens. All cylinder heads had fractured, missing material between the exhaust valve and a spark plug port. Piston compression and oil rings were fractured with missing pieces. Damage was consistent with detonation. Oil screen particles were mostly thin flakes; spectroscopy showed high peaks of carbon, oxygen, bromine, lead, and traces of iron, aluminum, chromium, and nickel.
Engine and Operational Notes
Both engines were equipped with Bendix PSJH-78D pressure carburetors. The Beechcraft E-50 Flight Handbook states mixture control is automatic and must remain full forward; manual leaning is only for emergencies. The Lycoming Engines Operator’s Manual for GS-480 series engines similarly advises not manually leaning engines with pressure carburetors. Lycoming’s online educational article discusses detonation, its causes, and prevention.