An overheated engine brought down a MQ-1B Predator over Turkey while the drone was collecting intelligence on the Islamic State in 2015, according to a newly released report.
A mechanical failure led the engine to overheat causing the Oct. 19, 2015, crash, according to an accident investigation report released Friday by Air Combat Command.
"The cause of the mishap was a pinhole leak in the elbow radiator of the coolant supply line," the document states.
In a release, the command said maintenance personnel who worked on the drone didn't realize the coolant line and a secondary mechanical line were too close to each other in the aircraft, "resulting in rubbing, chafing, and the pinhole leak."
"The loss of coolant inadvertently resulted in increased fuel flow, further degrading engine performance," the release states.
The aircraft was operated by airmen from the 20th Reconnaissance Squadron, Whiteman Air Force Base, Missouri.
The Air Force was still able to maintain contact with the aircraft and took it down in an unpopulated field, the Pentagon said at the time.
In addition, the report said the crew attempted to return the aircraft to its appropriate base after noticing "abnormal engine temperatures" but were unable to fly the MQ-1 at a safe altitude in a mountainous region.
"Despite implementing recovery procedures, there was no change to the overheat condition, and the aircraft continued to fly at a lower altitude," the release said.
The crew force-landed the drone in an unpopulated field with no risk to civilians or civilian property. The loss of the aircraft was valued at approximately $4.7 million, the command said.
That same month, another MQ-1 crashed in Iraq just southeast of Baghdad after the crew and the aircraft "lost link" with each other. The aircraft was recovered by Iraqi police and returned to coalition forces, the Pentagon said, as reported by Defense News.
The service plans to retire the MQ-1 -- in service for more than 20 years -- by 2018 and will move to an all MQ-9 Reaper remotely piloted combat aircraft fleet, officials announced last month.
The Air Force as of Sept. 30 had 129 Predators and 195 Reapers in the inventory, including both the active component and the National Guard, according to the service. Both aircraft are made by General Atomics Aeronautical Systems Inc. of San Diego.
