Occurrence
On August 21, 2023, at approximately 0730 local time, an Ag Cat G-164A agricultural aircraft, registration RP-R4456, operated by South Pacific Aerial Spraying Services (SPASS), experienced a loss of engine power during the initial climb after take-off from Lambayong Airstrip in Barangay Zeneben, Lambayong, Sultan Kudarat, Maguindanao, Philippines. The aircraft was on its fifth load of chemicals for a swathing operation when the pilot noted engine vibration followed by a decrease in engine RPM and eventual power loss. Unable to dump the chemical load, the pilot executed a forced landing in an open area. The aircraft touched down on its main landing gear, swerved left, and collided with two gemelina trees, coming to rest inverted at coordinates 6°51'27"N, 124°38'44"E, heading 291 degrees. The sole occupant, the pilot, sustained minor injury. Visual meteorological conditions prevailed at the time.
Investigation
The Aircraft Accident Investigation and Inquiry Board (AAIIB) of the Civil Aviation Authority of the Philippines conducted the investigation. The aircraft, manufactured by Allied Agcat Productions in 2015, was powered by a Pratt & Whitney R-1340 AN-1 HYD engine. Post-accident on-site examination revealed visible cracks near the spark plug on cylinder number three. The engine was removed and subjected to a teardown inspection at the SPASS hangar, witnessed by an AAIIB investigator. The inspection showed that the cylinder head had completely separated from the barrel between the cooling fins. The separation was attributed to pre-ignition or detonation stresses, which prevented the pushrods from operating the valves, leading to a total loss of engine power. No post-crash fire was observed, and the cockpit remained intact, contributing to survivability. The aircraft was not equipped with flight recorders, and no CAAP regulation required them.
Cause
The probable cause of the accident was the failure of the number three cylinder, resulting in a total loss of engine power.