Air Force Special Operations Command has stopped all flights for its entire fleet of CV-22 Osprey tiltrotor aircraft, citing safety issues over the last two months.
Lt. Gen. Jim Slife, head of Air Force Special Operations Command, on Tuesday ordered the stand-down of the service's 52 Ospreys "due to an increased number of safety incidents," according to an emailed statement.
"Since 2017 there have been four incidents involving hard clutch engagement during flight with 2 occurring in the past 6 weeks," Lt. Col. Rebecca Heyse, director of U.S. Air Force Special Operations Command Public Affairs, said in a statement.
Heyse added that the "length of the standdown is unknown" but that the command is working "to fully understand this issue and develop risk control measures to mitigate the likelihood of catastrophic outcomes."
News of the stand-down follows two fatal Osprey crashes this year that left a total of nine Marines dead. In addition, an ejector seat issue grounded the Air Force's F-35A Lightning IIs for two weeks.
The Osprey is a revolutionary, yet controversial, aircraft for the military. It combines the vertical takeoff and landing capabilities of a traditional helicopter with the long range of a turboprop plane.
The Navy's CMV-22 Osprey units are continuing to fly, but Cmdr. Zach Harrell with Naval Air Forces Public Affairs said the service is "aware of the issues affecting the U.S. Air Force CV-22 fleet and are closely monitoring our CMV-22 aircraft for similar occurrences."
The Marine Corps did not immediately respond to Military.com when asked whether the clutch issue extended to its fleet of Ospreys as well.
The Air Force began fielding its version, the CV-22, in 2007.
Heyse said the issue involves the hard clutch engagement, a part of the gearbox that connects the Osprey's Rolls-Royce engines to the rotor. The clutch is slipping, forcing the craft to land in order to regain stability. No airmen have been hurt or killed by the issue.
"At this point, there have been no injuries or deaths, due in large part to the skill and professionalism of our Air Commandos who operate the CV-22," Heyse said in an email. "The safety of our Airmen is of the utmost importance, therefore no AFSOC CV-22s will fly until we will determine the cause of the hard clutch engagements and risk control measures are put in place."
The stand-down follows a deadly crash this past June, when five Marines onboard an MV-22B Osprey were killed when the aircraft crashed near Glamis, California.
Additionally, in March, an Osprey crashed near Bodo, Norway, while participating in a military exercise, killing four Marines. That aircraft was based out of Marine Corps Air Station New River in North Carolina.
Investigators concluded that the pilots for the aircraft that crashed in Norway turned too sharply, causing the craft to lose altitude and speed, and ultimately crash.
Those crashes were the first deadly incidents with the aircraft since 2017. Between 1991 and 2006, while the aircraft was undergoing testing, there were four crashes resulting in 30 deaths.
The stand-down of Air Force Special Operations Command's Ospreys comes just weeks after the Air Force, Navy and Marines had to ground hundreds of jets after a widespread issue with ejection seats was discovered.
The Air Force also stood down its F-35s to investigate the parts. As of this week, the fighter jets are back in the air.
– Konstantin Toropin contributed to this report