What happened
On the morning of April 19, 2014, a Cessna 188B Ag-Truck, registration RP-R146, was conducting agricultural spraying operations in the Tagnanan area of Mabini, Compostela Valley. The aircraft, operated by Philippine Agricultural Aviation Corporation, was performing its eighth swathing mission of the day at an altitude of approximately 30 to 40 feet AGL.
While executing a shallow left turn at an airspeed of 85 kph, the pilot experienced a loud explosion and intense vibrations, accompanied by heavy white smoke emitting from the engine. The pilot attempted to restore power and engaged the fuel booster, but the engine failed to recover. Due to the low altitude and limited time, the pilot performed an emergency forced landing into a nearby banana plantation, roughly 25 meters from the edge of the active runway at Gadi Airstrip.
Upon impact with the uneven terrain, the aircraft sustained substantial damage. The engine continued to emit thick white smoke, prompting the pilot to quickly evacuate the cockpit. The pilot successfully exited the aircraft and moved to a safe distance, where local residents provided assistance. There were no injuries reported in the incident.
The investigation
The AAIIB investigation focused on the mechanical state of the engine and the maintenance oversight of the operator. Physical inspection of the engine cowling revealed significant damage to the upper crankcase of cylinders number 5 and number 6, including a large, four-inch diameter hole caused by a fracture.
Findings
- The primary cause of the engine power failure was the failure of 12-point spiral lock nuts that secure the connecting rod assembly for engine cylinders 5 and 6.
- Maintenance personnel for the operator failed to perform necessary duties to ensure the continued airworthiness of the aircraft.
- The operator's Approved Maintenance Organization (AMO) lacked a robust, independent quality assurance system to monitor maintenance compliance.
- A failure to comply with a critical service bulletin from Teledyne Continental Corporation, issued in 1999 regarding crankshaft fracture risks, was identified as a contributing factor.