A Reaper drone’s propeller ‘decoupled’ in Mediterranean crash
A $13 million Air Force drone crashed in the Mediterranean Sea when its propeller “decoupled” from its engine, an Air Force report on the mishap concluded.
Released Wednesday, the report details how, late last year, the Air Force drone operator controlling the MQ-9A Reaper — who was remotely piloting it from a base in Missouri on the opposite side of the world — quickly realized the unmanned aircraft had suffered a catastrophic engine failure and intentionally ditched it into the sea. The wreckage was not recovered, the report said, leaving few clues to the root cause of the failure, the accident investigation board found.
But the report peels back a window on some unique details of the daily life of “geographically separated” pilots and sensor operators who fly unmanned aircraft for Air Force attack squadrons.
The report specifically noted that investigators found no errors or negligence by the drone’s pilot or sensor operator, the maintenance crews, or the leadership overseeing the operation that contributed to the crash. The crew, the report found, was fully qualified and medically cleared to fly, and even though the mishap’s severe damage doomed the Reaper from the first seconds, the crew performed correctly as they tried to keep it in the air.
Mechanically, the report found, the MQ-9A was mission-ready and its maintenance records were up to date for the Dec. 16, 2024 flight.
But the report also illustrates several quirks of Air Force unmanned aerial vehicle (UAV) operations. For one, though the MQ-9A itself belonged to the 432nd Wing based at Creech Air Force Base, Nevada, the flight crew was assigned to the 20th Attack Squadron in Whiteman Air Force Base, Missouri. But though the 20th Attack Squadron has been a Reaper flying squadron since 2011, with pilots, sensor operators, planners and other operational staff all at Whiteman, the MQ-9As are not based there.
In fact, a July 2024 open house at Whiteman marked the first time one of the unmanned aircraft had ever physically visited the base, according to an Air Force release.
Trouble during a crew swap
The report notes the accident occurred during a mid-flight crew swap, another common procedure in UAV operations, when a fresh pilot or sensor operator relieves the one flying the craft at the Ground Control Station. After launching at 1300 Zulu time, or 8:00 a.m. in Missouri, the drone flew uneventfully for almost two hours towards its target (neither the drone’s launch site or target were named in the report). At about 10 a.m., the first pilot swapped out with a second. That second pilot, the report noted, had not been scheduled to fly but had been asked by the squadron’s supervisor for the day to step into the flight to relieve the first pilot during the 8-hour mission. The crew’s sensor operator also swapped with a second operator an hour later.
The Reaper continued to fly “safe and pretty much untouched,” the pilot told investigators, until close to 1700 Zulu over the Mediterranean — noon at Whiteman — when the flight’s original pilot returned to the control station. As the two pilots began to review the flight to again switch spots, warning lights flared as the engine dropped “from a normal torque operating range to a complete loss of torque within one second.”
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The second pilot, who stayed at the controls for the remainder of the flight, increased the throttles to full power as they worked to understand the malfunction, but got no response from the engine.
Over the next few minutes, the crew ran emergency checklists and picked out an airfield for an emergency landing. But the pilot soon “correctly assessed the engine as unrecoverable,” the report found, and realized the now-powerless drone could not glide far enough to reach land.
In a last-ditch attempt to regain engine thrust, the crew tried a “rack swap” — switching workstations in the control center. Though MQ-9A pilots and sensor operators control different systems during flight, both of their workstations in the control center are configured to fly the Reaper, a redundancy that allows crews to reset the system and swap places when a malfunction lies within the hardware of the pilot’s station, the report said.
But the rack swap made no difference.
As the Reaper glided lower, a monitor detected metal particles in the engine’s oil, a sign of significant internal damage. The crew shut the engine down and 23 minutes after the first warning, the drone hit the ocean.
The drone’s engine, the report found, had received a 6000-hour overhaul nine months earlier, and a 200-hour inspection in October. The Reaper had flown 618 hours in 32 sorties since August with no serious mechanical issues or any metal detection warnings.
The cause, the report said, was a failure within the Splined Coupling Assembly, a connection point between the engine and the propeller. Most likely, the report said, the specific cause was a Spiral Retaining Ring, a part with a history of rapid wear in the Reaper’s engine. Wear on the ring across the fleet had led to a change in repair schedules in MQ-9As, mandating the part be changed out twice as often as originally intended.
“There are multiple possible causes for early Spiral Retaining Ring wear,” the report concluded, “but without recovery of the physical evidence, none could be verified.”
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