Accident Summary
On 4 May 2023 at 7:33 Zulu time, an unmanned MQ-9A Reaper, tail number 18-4369, suffered a propulsion system anomaly approximately 9.5 hours into its flight. The mishap aircraft (MA) experienced an engine abnormality in which engine speed exceeded maximum operating limits, prompting the mishap crew (MC) to shut down the engine. The MA subsequently descended and impacted the water at an undisclosed location within the United States Africa Command (AFRICOM) Area of Responsibility (AOR). The MA was destroyed. There was no reported damage to civilian property, no injuries, and no fatalities. The loss of government property was valued at $21,794,224.
Sequence of Events
The MC, operating the MQ-9A remotely from a Mission Control Element (MCE) consisting of a mishap pilot (MP) and a mishap sensor operator (MSO), was conducting a mission. During the mishap flight, a mechanical failure within the MA's engine caused abnormal contact between rotating and static components. This led the Digital Electronic Engine Controller (DEEC) to decrease torque and then increase fuel flow in an attempt to maintain normal engine speed. The torque decrease resulted in a complete loss of thrust, initiating an uncontrolled descent. The increased fuel flow also produced indications of an engine fire to the MC. The MP shut down the engine due to the fire indication and loss of thrust.
With the engine out, no suitable recovery element or alternate airfield was within glide range. The MC, in coordination with the Air Operations Center and Persistent Attack and Reconnaissance Operations Center, intentionally directed the MA over water toward potential recovery assets. However, the MA continued descending until impact. The MA could not be recovered, preventing post-mishap inspection of the engine.
Cause Determination
The Abbreviated Accident Investigation Board President determined, by a preponderance of the evidence, that the cause of the mishap was a mechanical failure within the MA's engine at a mission location that prevented the MA from returning safely to a recovery location. Multiple potential mechanical failures could have caused the internal abnormal contact, but without engine inspection, a specific cause could not be identified.