The US Air Force is continuing its investigation into oxygen issues on its F-35As at Luke AFB, Arizona, including examining why the problem appears to be confined to one air base.

Luke AFB’s F-35As have been grounded since 9 June, after five pilots experienced “hypoxia-like symptoms” over the previous month. The air force began surveying pilots’ confidence at Luke when the incidents began in May and later expanded the survey across all USAF F-35 pilots, Col Todd Canterbury, director of the USAF F-35 Integration Office, told reporters on 19 June at Paris air show. Canterbury emphasised during his briefing that the service is not calling the incident a hypoxia problem, but rather a physiological event that could include hypoxia, hypocapnia or even hyperventilation.

In its examination, the air force looked at the aircraft’s low-rate initial production numbers as a possible common thread, Canterbury says. But the service found that Nellis AFB, in Nevada, Hill AFB, in Utah and Luke AFB have LRIP 6, 7 and 8 aircraft. Pilots at Luke AFB are operating Block 2b and 3i software.

"It’s too early to identify a root cause," he says. "But they specifically looked at production lots, they looked at software variants, all the components have software pieces, they drilled all the way down to oxygen control, drill all the way down to maintainers that maintain that system to see if there was a procedure that they didn’t comply with, so that’s the granularity that they’re really drilling down to."

Canterbury appeared to step away from prescribing a fix for the aircraft’s on board oxygen generator system (OBOGS), even after officials at Luke voiced concerns about the OBOGS’ robustness last week. Although the USAF’s pilot survey identified some areas where the service could focus its technical expertise, Canterbury is cautious over funding a fix before the root cause is found.

"It’s far too early to identify any single technical area where we can pour resources to get those fixed," he says. “We don’t want to chase rabbits and waste taxpayer money on that."

In the meantime, the commander at Luke AFB can make local decisions to increase pilot confidence and decrease their vulnerability to oxygen issues, such as implementing an artificial speed restriction, he adds.

"We know exactly what altitudes that this instance happened," he says. "So if they simply stay out of that altitude regime for a little while, [it will] build their confidence."

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