Accident Details
On December 31, 2019, at approximately 1415 central standard time, an Enstrom F28A helicopter, registration N57SJ, sustained substantial damage when it nosed over during a forced landing following a partial loss of engine power. The nose-over resulted in separation of the tailboom and damage to the main rotor system and fuselage. The helicopter was being used for an instructional flight under Title 14 Code of Federal Regulations Part 91, operated by a private individual. Visual meteorological conditions prevailed, and the flight was not operated on a flight plan. The local flight originated from Salaika Aviation Airport (07TA) in Danbury, Texas, at an unconfirmed time.
Flight History
The certificated flight instructor reported that he and his student had departed for a second pattern during a training mission. After the helicopter turned onto the crosswind leg of the traffic pattern, the engine suddenly began to run rough and lost significant power. The instructor took control and executed an autorotation into a clearing. After flaring and touching down, the helicopter's skids sank into soft mud, the rotor blades contacted the ground, and the helicopter rolled onto its side. Both the student pilot and flight instructor were not injured.
Post-Accident Examination
Following the accident, an examination of the engine revealed that a portion of the intake valve for the No. 3 cylinder had broken off and migrated into the No. 1 cylinder. There, it became lodged between the No. 1 intake valve and its seat, holding that valve in the open position, which contributed to the partial loss of engine power. The operator reported this finding.