The Air Force has determined that a 2017 mishap that led to the disappearance of an MQ-1B Predator remotely piloted aircraft was due to a lost satellite link and the inability to reestablish the link for “unknown reasons,” the service’s Air Combat Command (ACC) said Jan. 7.

The aircraft was lost in the U.S. Central Command (CENTCOM) area of responsibility on Sept. 4, 2017, while being controlled via the 432d Air Expeditionary Wing at Creech Air Force Base, Nevada. The operating aircrew lost the ability to control the aircraft about 16 hours into the mission, and the current location of the Predator remains unknown, according to an ACC Abbreviated Accident Investigation Report released Monday.

An MQ-1B Predator from the 62nd Expeditionary Reconnaissance Squadron Detachment 1 takes off from the flightline at Jalalabad Airfield, Afghanistan, Feb. 4, 2016. The MQ-1B is an armed, multi-mission, medium-altitude, long-endurance remotely piloted aircraft is employed primarily as an intelligence-collection asset and secondarily against dynamic execution targets. (U.S. Air Force photo/Tech. Sgt. Robert Cloys)

“The cause of the mishap was a lost link event followed by an inability to reestablish link for unknown reasons,” ACC said in a press statement accompanying the report. “A lost link event occurs when the aircraft crew loses satellite link with the aircraft.”

At the moment of the mishap, the MQ-1 was operating normally at a medium altitude of 13,000 feet, the report said. After standard crew changeover briefs, the mishap crew lost complete video and command link and was no longer able to monitor or control the aircraft. Weather was not a factor, nor were the cockpit equipment and its maintenance. The crew initiated an emergency checking for aircraft that have lost a satellite link, but the issue was not resolved.

The aircraft wreckage has yet to be found, and thus the hardware could not be analyzed, per the report. Radar controllers and one fighter aircraft were unable to detect the MQ-1 in the area of the lost link event.

The estimated cost of the missing MQ-1B is just over $4 million, the report said. No known injuries or damage to other government or private property were reported. General Atomics Aeronautical Systems Inc. manufactures the Predator.