U.S. Air Force Special Operations Command (AFSOC) is still investigating the root cause of the slippage of a sprag clutch in one of the engines of the Bell [TXT]/Boeing [BA] CV-22 in two recent incidents that caused a temporary grounding, lifted last week.
“We’ve had 15 of these [incidents] across the [V-22] fleet over the last dozen years or so,” Air Force Lt. Gen. James Slife, the AFSOC commander, told an Air & Space Forces Association Warfighters in Action forum on Sept. 7. “Four of them have been AFSOC. 11 of them have been Marine [V-22s]. We’ve all understood that this is a mechanical problem. What’s eluded us is the root cause. Why is the clutch slipping in the first place? At AFSOC, we’ve had two of these events in the last couple of months now. My standdown was an opportunity for us to bring some attention to this in the engineering enterprise.”
“When we actually looked at the data behind all of these [incidents], what we found was that virtually all of them occurred in the exact same regime of flight,” Slife said. “Virtually all of them occurred with gearboxes with the same amount of flight time in the gearboxes…Getting down to that level of analysis allowed us to modify some of our operations practices to put some restrictions in place to keep our crews out of the environments in which this is most likely to happen while we continue to search for the root cause issues.”
“Late last week, we were able to hammer out the specific operational restrictions we were going to put in place,” he said. “It’s things like how we manage our power settings during take-off, how frequently we do vertical take-offs, versus short take-offs. If you’ve got a runway available, use the runway–those types of things. I feel pretty comfortable that appropriate mitigation measures are in place. In AFSOC, we haven’t had a catastrophic mishap…Each one of them results in kind of a Christmas tree of caution lights in the cockpit, and some pretty swirly flight control input. I’m really proud of how our crews have been able to safely land these airplanes, but I’d rather they not have to demonstrate their superior skill because we put superior controls in place to prevent them from having to do that.”
In one of the recent CV-22 sprag clutch incidents, an aircraft in an Arctic exercise in northern Norway had to make an emergency landing last month in the nature preserve of Stongodden on the island of Senja.
“We’re in the midst of a recovery process to get that airplane to a place where we can swap out the engines and the gearboxes and all of the things that need to be replaced,” Slife said on Sept. 7. AFSOC has had an inventory of 52 CV-22s out of a planned 54.