August was quite the month for the DoD’s rotary aircraft, with two platforms grounded due to technical issues – while the United States Air Force also was able to take delivery of its latest platform. Even if some of the rotors weren’t moving, it might have been enough to make aviation watchers’ heads spin.
The Air Force had been forced to ground its entire fleet of CV-22 Osprey indefinitely, following four incidents of “hard clutch engagement during flight” since 2017, with two of those occurring just in the previous six weeks. On August 16, Lt. Gen. Jim Slife of the Air Force Special Operations Command was forced to issue the “safety standdown” due to the increased number of incidents.
The CV-22 Osprey, produced by Bell Helicopter Textron in Amarillo, TX, is a tiltrotor aircraft that combines the vertical takeoff, hover, and vertical landing qualities of a helicopter with the long-range, fuel efficiency, and speed characteristics of a turboprop aircraft. The mission of the CV-22 is to conduct long-range infiltration, exfiltration, and resupply missions for special operations forces.
There are currently 52 CV-22s in service with the Air Force.
Ospreys Grounded
As of press time, the Air Force has continued to determine the cause of the issue and has been working to “develop risk control measures to mitigate the likelihood of catastrophic outcomes.”
“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,” command spokeswoman Lt. Col. Becky Heyse said in a statement to Breaking Defense.
No injuries or deaths have been caused by the issue “due in large part to the skill and professionalism of our Air Commandos who operate the CV-22,” Heyse added. It is unknown how long the aircraft will be grounded.
Marine Ospreys Still Flying
The Air Force’s decision to ground the CV-22 Osprey was made after two accidents that killed nine United States Marines earlier this year involving the Marine Corps’ MV-22B version of the aircraft. In June, an Osprey crash in California killed five Marines, while a prior crash in Norway in March also resulted in the death of four Marines.
However, the U.S. Marine Corps said last month that it would not ground its MV-22 Osprey fleet over a clutch problem. The service has known about the issue with hard clutch engagement since 2010, and as a result has trained its pilots on how to respond when such emergencies happen, Marine Corps spokesman Maj. Jim Stenger said in a statement to reporters.
This problem typically occurs when the clutch, which connects the propeller’s rotor gear box to its engine, slips and subsequently causes the Osprey to transfer the power load to the other engine almost instantaneously so the aircraft can keep from crashing. The original gear box’s clutch then reengages, the power load transfers back in a span of milliseconds and the large transfer of torque causes the Osprey to lurch.
The Marine Corps has distributed guidance on the hard clutch engagement issue, while the service would conduct briefings with Osprey aircrew and maintainers. The Marine Corps is now planning to work with the V-22 program office and industry partners to develop additional alert indicators in the cockpit over the long term, which could alert pilots when a clutch problem is emerging.
The Marines currently maintain a fleet of about 296 Ospreys, and they have flown them for 533,000 flight hours.
History of Osprey Issues
Since 2010, the V-22 program has experienced a total of 15 instances of hard clutch engagement, including 10 with the United States Marine Corps Ospreys.
The United States Navy also confirmed last month that it has not experienced any problem with its CMV-22 variant, the newest in the Osprey fleet, which began its first deployment in the summer of 2021.
A defense official said that more than two-thirds of these clutch-related problems have occurred seconds after takeoff when power is quickly applied. As a result, the Marine Corps has said it will reinforce its takeoff maneuvers, and further remind aircrews of the importance of checking gauges. Those instruments often alert the aircrew that such a problem is about to occur so the pilots can quickly and safely land the aircraft.
The Army Grounded its Chinooks
The United States Army doesn’t operate the Osprey, but instead faced its own rotary aircraft issue last month – and announced on August 31 that it was forced to ground its entire fleet of CH-47 Chinook helicopters while it works to fix fuel leaks that caused an unspecified number of engine fires.
The Army announced in a statement that it would ground the entire fleet of about 400 aircraft, “out of an abundance of caution,” but also added no deaths or injuries resulted from the fires.
“The Army has identified the root cause of fuel leaks that caused a small number of engine fires among an isolated number of H-47 helicopters and is implementing corrective measures to resolve this issue,” Army spokesperson Cynthia Smith said in an email to Military.com on Wednesday. “The safety of our soldiers is the Army’s top priority, and we will ensure our aircraft remain safe and airworthy.”
The Chinook has been a workhorse of the U.S. Army fleet since it was first introduced more than 60 years ago. It has carried troops and cargo on battlefields from Vietnam to Afghanistan and Iraq. The current model, the CH-47F, is the Army’s “only heavy-lift cargo helicopter supporting combat and other critical operations.”
Honeywell International, which manufactures the engines of the Boeing-made Chinook, has reported that the issue is likely related to a problem with the O-rings, which are used to create a seal between engine parts to prevent leaks.
First MH-139A Grey Wolfs Delivered
It hasn’t been all bad news for the U.S. military when it comes to rotary aircraft. In August, Boeing announced that it had delivered the first four MH-139A Grey Wolf helicopters to the United States Air Force after the aircraft had received certification from the Federal Aviation Administration (FAA).
The Grey Wolf is based on the commercial AW139, made by Italian-based Leonardo, and it had previously been evaluated by Europe’s civil aviation safety authority. However, Boeing still was required to obtain the FAA certification before the helicopter could be delivered to the Air Force for evaluation.
The program is currently about a year behind schedule, but with the aircraft now delivered, the service can start its military utility testing.
“This milestone really represents the beginning of Air Force testing for the Grey Wolf,” said Lt. Col. Mary Clark, a Grey Wolf pilot with the 96th Operations Group, who previously worked on requirements for the program. “We can now open up those test points for the military and push the envelope more to ensure we’re delivering that operational capability the units need out of the helicopter.”
The Grey Wolf has been touted as a modern, versatile aircraft offering greater range, speed, and endurance than the UH-1N Huey it will eventually replace. The Air Force expects to buy a total of 80 MH-139As to replace its aging Huey fleet. The Air Force intends to buy five Grey Wolf helicopters for $156 million in the fiscal year 2023 (FY23) and has already procured the first eight MH-139As. Boeing successfully beat out Lockheed Martin and Sierra Nevada Corp. for the $2.4 billion contract in 2018. The Italian-based Leonardo builds the commercial A139 in Philadelphia, which Boeing then modifies with military-specific technologies as the MH-139A Grey Wolf.
