Partial Loss Of Engine Power Due To The Fatigue Failure Of An Engine Cylinder...

Location: Honea Path, South Carolina Accident Number: ERA20LA326
Date & Time: September 21, 2020, 19:49 Local Registration: N1524M
Aircraft: Stearman E75 Aircraft Damage: Destroyed
Defining Event: Loss of engine power (partial) Injuries: 1 Serious, 1 Minor
Flight Conducted Under: Part 91: General aviation - Personal

Analysis: The airplane departed and was in a continuous climb at 70 mph, at 2,500 rpm. The pilot observed a cylinder depart the engine and experienced a partial loss of engine power. A video of the event recorded the sound of the engine becoming quieter and the tachometer showed a continuous 1,000 rpm reading following the separation. The video captured the airplane maneuvering over open fields suitable for a forced landing as it descended back towards the departure airstrip. The recording ended before the airplane was destroyed by contact with trees and terrain 500 feet prior to the landing strip.

Examination of the nine-cylinder radial engine revealed a separated cylinder, with all of its associated mounting studs fractured. Three of the mounting studs displayed features consistent with fatigue, likely due to inadequate torque applied at overhaul, which was completed less than 100 aircraft hours prior to the accident.

Probable Cause and Findings: The National Transportation Safety Board determines the probable cause(s) of this accident to be -- The partial loss of engine power due to the fatigue failure of an engine cylinder and the pilot’s subsequent decision to overfly several suitable forced-landing sites while attempting to return to the departure airstrip. 

FMI: www.ntsb.gov