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Oxygen-generator inquiry covers AF fighters

The Air Force investigation into problems with the F-22’s oxygen-generation systems extends beyond the Raptor and includes fighters the service has been flying for decades.

A safety investigation board, headed by an Air Force flag officer, is looking at problems with the On-Board Oxygen Generation Systems of the F-16, F-15E, A-10, F-35 and T-6 aircraft, service officials said May 6, three days after all F-22s were grounded because of a spike in hypoxia incidents during flight.

“The OBOGS safety investigation is looking at all oxygen generation systems, casting a broad net for comparison of designs and functionality, thereby peeling back all aspects to seek any peculiarities of design, operation and performance,” said Capt. Jennifer Ferrau, an Air Force spokeswoman representing Air Combat Command.

“No particular subsystem had stood out as an area of concern, so this investigation seeks to identify any area of concern,” she said.

The board conducting the investigation includes safety investigation officers, pilots, doctors, engineers, maintainers and other specialists.

Hans Weber, who sat on the Federal Aviation Administration’s Research, Engineering and Development Advisory Committee and is the president of Tecop International, a San Diego consulting firm, said the Air Force likely does not yet have a good idea of what the problem with the OBOGS is.

“I’m sure it’s a surprise to everybody with a system that has been in operation for decades that all of a sudden, they run into problems with it,” he said.

Each generation of aircraft improves upon the technology, Weber said.

It is possible that during the drive to shrink and lighten the OBOGS for the F-22, engineers may have inadvertently introduced a problem; there may be something unique about the F-22’s OBOGS design, Weber said.

“We haven’t had any such problem for a long, long time; that tells us something,” he said.

The Air Force would not release any other details about the investigation, except that the OBOGS-specific investigation started in January. Nor would the Air Force say whether pilots flying aircraft other than the Raptor had experienced hypoxia-related incidents.

The fact that the service ordered a fleetwide stand-down of the Raptor indicates a potentially significant problem, but it does not indicate a systemic issue with the U.S. tactical aircraft fleet, said Mark Gunzinger, an analyst at the Center for Strategic and Budgetary Assessments in Washington and a former Air Force pilot.

Just to be safe

“There is not a huge, major problem with the entirety of the tactical aviation force, but it’s better to be safe than sorry,” he said.

However, Weber said the fact that the entire Air Force tactical fighter fleet is being investigated suggests that a wider problem with the OBOGS exists.

“The fleet investigation has a fairly high hurdle. There has to be something that is a big question mark or something that is a suspect part or system,” he said. “What they’re telling us here is that the investigation has not fingered any particular part.”

Both agree that there is a particular problem with the Raptor, however.

“The F-22 grounding itself implies that this is probably something that is a little more than a normal thing with the system,” Gunzinger said.

However, problems with subsystems are not unusual. The B-52 bomber, for example, has had problems with its brakes in previous years, he said.

The OBOGS’ most likely problem is the long-term reliability of certain components, Weber said. Parts that operated normally during tests might be wearing out more quickly than expected, he said, which could lead to the eventual modification and replacement of the parts as a potential fix.

If the problem’s cause is a subsystem that can be easily replaced, the grounding should be resolved fairly quickly, Gunzinger and Weber said. However, deeper structural defects with the OBOGS will take longer to fix.

In either case, in the longer term, modifications are likely to be necessary to resolve the problem, Weber said.

However, “I wouldn’t anticipate that this would be a very lengthy grounding,” Gunzinger said.

Weber said that of the aircraft named, the F-35 is most likely at risk for a similar problem. Both the F-22 and the F-35 use late-model OBOGS designs built by Honeywell. The other aircraft are at less risk because they have older systems built by another manufacturer, Cobham.

Neither company offered substantial comment.

The Pentagon’s F-35 program office said that while the F-35 had absorbed many lessons from the F-22 program, the systems onboard the newer jets have little in common with the Raptor.

“The F-35 and F-22 have common aircraft and oxygen-system suppliers, but the systems are very different. The program has leveraged the lessons learned from F-22 development to enhance the F-35 across all subsystems, including the Onboard Oxygen Generating System,” said F-35 program office spokesman Joe DellaVedova.

The F-35 program is supporting the investigation into the Raptor OBOGS problem, DellaVedova said.

“At this time, the program office does not see any commonality in the potential causal factors that the F-22 program is investigating,” he said.

The Navy said the F/A-18 fighter is not under investigation. The jet is known to use an OBOGS similar to those on Air Force planes that has had problems in the past.