An Air Force MQ-9 Reaper drone worth $13 million plunged into the Mediterranean Sea last December after its propeller disconnected and fell off in midair, according to the findings of an official accident investigation.

The incident highlights the vulnerability of even the most advanced military aircraft when a small but critical component fails.

The MQ-9, assigned to the 432nd Wing at Creech Air Force Base in Nevada, was found to have likely experienced a mid-flight failure of a crucial ring that secured its propeller in place. This failure led directly to the loss of the propeller and ultimately to the crash on December 16.

The Reaper, operated remotely by a pilot and sensor operator from the 20th Attack Squadron at Whiteman Air Force Base in Missouri, had taken off from an undisclosed location within the U.S. European Command’s area of responsibility, the accident investigation board’s report, released on July 30, revealed.

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At approximately 5 p.m. Greenwich Mean Time, the drone was cruising at normal altitude and speed when the engine torque suddenly dropped, losing all torque within a single second.

In the same moment, the engine speed surged beyond its normal operating limits, and warning alerts began to appear. Although the pilot responded by pushing the throttle to full power, the torque remained at zero.

Initially, the Reaper managed to maintain altitude, but soon it began losing airspeed and started to descend.

Recognizing the seriousness of the situation, the crew initiated emergency procedures in an attempt to control the descending aircraft.

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They turned the Reaper toward the airport from which it had departed and identified a remote, uninhabited location that could serve as a safe spot for a forced landing if the situation worsened.

Roughly 15 minutes into the emergency, the drone’s systems detected metal debris in the engine oil. Because of this discovery, the crew decided against attempting an engine restart. Shortly afterward, the engine shut down completely.

As the Reaper continued to lose altitude, the operations superintendent on duty instructed the crew to crash it into the sea, which they did at 5:23 p.m.

The drone sank into the Mediterranean and could not be recovered, leaving investigators without the physical evidence needed to confirm the exact cause of the failure. Nevertheless, General Atomics, the manufacturer of the Reaper, analyzed the aircraft’s data logs and determined that it had lost engine torque when the propeller “decouple[ed]” from the engine.

The report noted that two of the aircraft’s systems began recording different speeds, something that could only occur if the propeller had disconnected.

Investigators reported that General Atomics identified the most likely cause as the failure of a spiral lock ring inside the gearbox. The company declined to provide further comment.

According to the report, these rings are known to suffer from excessive wear and tear over time, sometimes to the point of failure.

Honeywell, which manufactures the MQ-9’s engine, had responded to this issue in recent years by replacing the rings after every 3,000 flight hours in an effort to reduce failures.

The report noted that this change did lead to a reduction in such incidents. However, the Reaper involved in the December crash was only about halfway to its next scheduled overhaul and ring replacement. This means the ring failed much earlier than expected.

Investigators explored several theories about why the ring might have worn out prematurely. Because the aircraft remains unrecoverable at the bottom of the sea, they could not confirm any of those possibilities.

Even so, the investigation concluded that the flight crew followed all required procedures, and there was no evidence that mission planning or preflight checks contributed to the mishap.

The crash underscores the reality that a single mechanical failure, especially in an essential component like a propeller retention ring, can lead to the loss of an entire aircraft.

At the same time, it demonstrates the complexity of military aviation, where human skill and technological safeguards cannot always overcome the sudden breakdown of a small but indispensable part.

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