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USAF pinpoints root cause of F-22 Raptor’s oxygen woes (Read 3486 times)
 
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USAF pinpoints root cause of F-22 Raptor’s oxygen woes
Aug 2nd, 2012 at 9:46am
 
USAF pinpoints root cause of F-22 Raptor’s oxygen woes

By: Dave Majumdar Washington DC
11:23 24 Jul 2012   

The US Air Force has officially settled on the root cause of a series of "hypoxia-like" incidents that have been plaguing the service's fleet of Lockheed Martin F-22 Raptors.

The USAF had earlier narrowed down the potential root cause to either contamination or an air quantity problem. "We have eliminated one of the hypotheses that the air force scientific advisory board postulated as a potential root cause for the hypoxia-related incidents and that was contamination," says USAF chief of staff Gen Norton Schwartz. "We have the data that has confirmed that."

The USAF has also gathered data that indicates that the problem has to do with the amount of oxygen that is reaching the pilot, Schwartz says. Based on tests conducted inside an altitude chamber and a centrifuge, the USAF has concluded that a combination of hardware defects with the pilot's life support gear contributed to the problem.

"Part of that is the upper pressure garment of the g-suit assembly," Schwartz says. "Part of that has to do with hose and valve and connection hardware in the cockpit."

The USAF has a deliberate plan to modify and test that equipment under the "most demanding conditions," the general says. "That will begin to hit the field in September," he adds.

But despite the USAF having found the root cause of the hypoxia problems, the service will maintain most of the restrictions imposed upon the F-22 fleet until the all of the modifications reach operational flight crews. The aircraft is flying with an altitude restriction of 44,000ft and must remain within 30 minutes of an airfield-but there are also a number of maneuvering limitations that are in place.

"We are confident that we have managed the risk associated with continuing operations in the F-22," Schwartz says. "Minimized, perhaps not eliminated, until the modifications are in place."

Asked why the problems with the Raptor's life support systems were not caught earlier during the jet's extensive developmental and operational test phases, Schwartz says that human physiology is not well understood at the combination of altitude and g-loadings that F-22 pilots routinely operate at.

"This is a unique airplane," Schwartz says. "You can pull 6Gs at 50,000ft. Tell me what other airplane, ever, can do that?"

There are aspects of the Raptor's performance at high altitude, which from the standpoint of human physiology, are not well understood. "In some respects, the testing did not reveal the shortcomings we have recently discovered."

In the early days of jet aviation, Schwartz says, the aerospace physiology community played a very large role. But in recent years, that base of expertise has atrophied. "The engineering know how that's associated with that has diminished, I think, even on a national basis."

Schwartz says the lesson the USAF must draw from the F-22 experience is that the service must pay much more attention to man-machine interfaces when developing an aircraft that offers such extreme performance levels. "We missed some things, bottom-line," he says.

US secretary of defense Leon Panetta has mandated that the USAF will use a phased approach to lifting the restrictions on the aircraft. The USAF must demonstrate the results to Panetta after every step it takes, Schwartz says.

Panetta was briefed 20 July on the USAF's conclusions by USAF secretary Michael Donley and Schwartz, says acting assistant secretary of defense George Little.

Panetta is easing one condition on the USAF's Raptor operations-the jets will be allowed to deploy to Kadena, Japan, via a route over the northern Pacific island chain, Schwartz says. That would necessitate increasing the time and distance the aircraft is allowed to maintain away from an airfield from 30 minutes to 1.5 hours.

The deployment will take place "in days," Schwartz says. But the USAF tankers that will accompany the squadron-sized deployment must have an F-22 pilot onboard to provide guidance in case of an emergency, Schwartz says. Moreover, the tankers will carry enough JP-8 to refuel the F-22s at low altitude in the event the fighters are forced to descend.

The USAF is deploying the jets now rather than in September "because there is an operational requirement," Schwartz says. "And the birds are ready to go."
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Re: USAF pinpoints root cause of F-22 Raptor’s oxygen woes
Reply #1 - Jan 9th, 2013 at 6:08am
 
USAF to field F-22 life support mods this January

By:   Dave Majumdar Washington DC

The US Air Force expects to start fielding life support systems modifications for its fleet of Lockheed Martin F-22 Raptor air superiority fighters this January.

"UPG [upper pressure garment] valves are being shipped now, and the vests will be modified locally," says the USAF's Air Combat Command (ACC). "We expect units will start flying with the modified vests later this month, which alleviates the current restriction that has them flying without the vests at altitudes below 44,000 feet unless otherwise directed."

The Raptor, which is regarded as the USAF's premier air-to-air fighter, had been operating under a number of operational limitations because of a suspected problem with the aircraft's onboard oxygen generation system (OBOGS). The problem was severe enough that the USAF was forced to ground the Raptor for four months in 2011 after more than a dozen "physiological incidents" with symptoms resembling hypoxia. After the USAF concluded that the pilot's Combat Edge upper pressure garment was the source of the problem, the service has slowly been lifting restrictions on the Raptor's operations. Other than the altitude limitation, the only other remaining restriction on F-22 is that the aircraft is currently precluded from executing the Alaska air sovereignty mission.

Once an automatic back-up oxygen system (A-BOS) is fielded, F-22s based at Joint Base Elmendorf-Richardson will be cleared to perform the air sovereignty mission over Alaska. "This meets the condition for approving F-22s to resume the air sovereignty mission in Alaska," ACC says. "A-BOS units are now installed on aircraft for evaluation purposes, and we remain on track to begin modifications to other aircraft--starting with Elmendorf--within the next couple months."

Currently, other aircraft, mostly Boeing F-15C Eagles, have been covering for the Raptors.

The USAF is also investigating the Raptor's OBOGS oxygen schedule, which might be providing too high an oxygen concentration, leading to a condition called acceleration atelectasis. "We're analyzing the O2 scheduling issue, but there's no firm timeline associated with testing or potential modifications so I can't characterize how far along that is other than to say it's ongoing," ACC says. "The major step taken by the task force with respect to O2 concentration last spring was to reduce pilots' susceptibility to atelectasis by discontinuing the requirement to fly at a "max" OBOGS setting."

Kevin Divers, a former USAF F-22 flight test engineer and aerospace physiologist, says, "Atelectasis was a problem before the "max" setting requirement, so norm doesn't reduce it from where it was when the issues started happening."

Further, Divers says, the USAF has already studied a modified Raptor's oxygen concentration schedule in detail. "It was all set to go, just not funded," he says. But ACC counters, "Further adjustments to O2 scheduling require more study, since the benefits or unintended consequences of revising the schedule are not as clear-cut as some sources might suggest."

But Divers goes further, he says that the USAF has missed the true root cause of the Raptor's oxygen woes. "They still are missing it and there will be issues that creep up," he predicts. "The vest fix will make them more comfortable, but won't solve the root cause."
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Flight Restrictions Lifted for F-22s with Auto Oxygen System
Reply #2 - Apr 4th, 2013 at 6:46pm
 
Flight Restrictions Lifted for F-22s with Auto Oxygen System
Apr. 4, 2013 - 01:43PM   
By BRIAN EVERSTINE - defensenews.com

Most of the Air Force’s F-22 fleet has returned to unrestricted flight operations after being limited for nearly a year to flying within 30 minutes of a safe landing area and at lower altitudes because of safety concerns.

Air Combat Command announced today that the restrictions mandated by then-Secretary Leon Panetta in May have been lifted for F-22s that have been retrofitted with automatic backup oxygen systems. The new oxygen systems will be installed on all of the stealth fighters by July 2014.

F-22s have resumed aerospace control alert missions in Alaska and are no longer restricted to flying within a 30-minute flying distance from a suitable airfield, said ACC spokeswoman Kelly Sanders.

The Air Force grounded the F-22 fleet for four months in 2011 after more than a dozen pilots complained of hypoxia — nausea, dizziness and disorientation — while in flight. The Defense Department placed limits on altitude and flying distance from airfields in May, weeks after two F-22 pilots appeared on “60 Minutes” and said they were afraid to fly the plane.

In July, investigators traced the primary cause of pilot hypoxia to a leaky valve in the pilots’ Combat Edge life-support vest, which caused the vest to inflate unnecessarily at lower altitudes and restricted the pilots’ ability to breathe. New valves were installed in January.

The Air Force also determined the F-22 should be equipped with an automatic backup oxygen system, instead of the manually operated backup that had been installed on the jet. In a fatal crash in Alaska in November 2010, Air Force pilot Capt. Jeff Haney was unable to activate the manual backup oxygen as his plane spun out of control, according to a crash investigation. Haney’s death led to two years of investigations and charges that the Air Force was not adequately addressing pilots’ complaints.

Installation of the backup oxygen system began at Nellis Air Force Base, Nev., in January. F-22s in Alaska that handle the aerospace alert mission installed the system in February.

Earlier this month, F-22s from the 94th Expeditionary Fighter Squadron deployed to Osan Air Base, Korea, as a part of exercise Foal Eagle.
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