The Air Force knows what failed on Osprey in a crash in Japan. It is still looking for why it failed
WASHINGTON — The Air Force Special Operations Command said Tuesday it knows what went wrong with the CV-22B Osprey that led to a November crash in Japan that killed eight service members. But it still doesn’t know why the failure happened.
Hundreds of Osprey aircraft from the Air Force, Marine Corps and Navy have been grounded since December 6 because of the crash. There are two investigations investigating the crash in Japan: a safety investigation board, which conducted a privileged internal review privately to help inform pilots and crews, as well as an accident investigation board, the official administrative review. Both are still ongoing.
In addition, Air Force Special Operations Command is undergoing its own extensive review of its CV-22 Osprey program, and while the command has said it knows what failed, it has not made those details public.
“At this time the material failure that has occurred is known, but the cause of the failure has not yet been determined. Technical tests and analyzes are carried out to determine the cause of the material failure, a crucial part of the investigation. Any disclosure of findings before the conclusion of the investigation is premature and presumptuous,” the Air Force Special Operations Command said in a statement released Tuesday.
The Air Force, Navy and Marine Corps have been coordinating efforts to determine when the Osprey crews can safely return to the airspace. Each service will make its own decision, and the Air Force said it will return its fleet of about 50 Ospreys to flight, “the priority is to inform our purposeful return to flight and ensure that CV-22 aircrews and maintainers have the information they need to prevent future accidents.”
The Osprey is a tiltrotor aircraft that can fly both as a helicopter and as an airplane.
Late Monday, NBC News reported that the crash was related to chipping of the Osprey’s proprotor gearbox. When wear and tear causes small pieces of metal to break off the aircraft’s gears, it can release hazardous metal waste that can damage the engines. The gearbox has been scrutinized in several Osprey accidents and some parts of it have worn out faster than expected. In January 2023, the Department of Defense awarded Bell-Boeing $12.7 million to improve gearbox design for all Air Force, U.S. Marine Corps, and Navy Osprey variants.
The Air Force Special Operations Command could not say whether a transmission chip caused the accident. However, it would not be the first time that a chip problem was linked to an accident involving the Air Force Special Operations Command Osprey.
In July 2013, an Osprey suffered a proprotor gearbox chip in flight. Due to the size of the debris, the entire gearbox had to be replaced. According to data obtained by The Associated Press, an Osprey made a precautionary landing in January 2014 after experiencing another in-flight gearbox chip.
Chipping can be caused by a variety of factors, including a lack of lubrication of the gears, or the fact that the gear teeth are subject to overload, said Rex Rivolo, a retired Air Force pilot who analyzed the Osprey for the Pentagon’s Test and Evaluation Office . 1992 to 2007 as an analyst at the Institute for Defense Analyses.
The Osprey has a chip detector that alerts the crew if metal fragments are detected, alerting them that pieces of metal are breaking off the gears. “The procedure is to land immediately,” Rivolo said. “Most chip warning lights are made of very small pieces of metal and are harmless, and the plane lands safely.”