Summary
On 16 December 2024, at approximately 17:00:00 Zulu time, an MQ-9A Reaper, tail number 13-4225, descended from its cruising altitude and impacted the water in the Mediterranean Sea. The aircraft had been launched by a launch and recovery element crew and control was transferred to a mission control element at Whiteman Air Force Base, Missouri. The mishap involved personnel from the 20th Attack Squadron. There were no reported injuries, no damage to civilian property, and no fatalities. The aircraft was not recovered, resulting in a loss valued at $13,154,585.00.
Sequence of Events
At 17:00:18 Z, the engine torque display dropped from normal operating range to zero within one second. The aircraft lost airspeed and began an uncontrolled descent. At 17:00:46 Z, throttle was increased to full power, but torque did not respond. Over the next 16 minutes, the mishap crew executed multiple emergency checklists to maintain control and restore thrust. At 17:16:00 Z, metal debris was detected in the engine oil, indicating internal damage. The pilot shut down the engine, and the crew performed a forced landing into the water. At 17:23:02 Z, datalink was lost, and the last data showed altitude near the water surface.
Investigation Findings
The Accident Investigation Board determined, by a preponderance of evidence, that the cause was a failure within the Splined Coupling Assembly. This failure led to a sudden and permanent mechanical decoupling of the propeller from the engine, resulting in unrecoverable loss of thrust. Data logs showed that after decoupling, the Digital Electronic Engine Controller and the Engine Fuel Interface Unit indicated different but accurate speeds, which can only occur if the propeller is decoupled from the engine. General Atomics Aeronautical Systems Incorporated reported the Spiral Retaining Ring as the most likely cause, but the definitive cause could not be discerned because the wreckage was unrecoverable.
Probable Cause
The accident was caused by a failure within the Splined Coupling Assembly, which caused the propeller to decouple from the engine, leading to a total and permanent loss of thrust. The most probable component failure was the Spiral Retaining Ring, but without recovery of the aircraft, the exact failure mechanism could not be confirmed.