Brig. Gen. Brook Leonard, the 56th Fighter Wing commander, explains what was found during an investigation into F-35 issues on Luke Air Force Base. Sam Caravana/

Military investigators have not discovered the cause for recent bouts of hypoxia-related incidents impacting F-35 pilots at Luke Air Force Base, but the West Valley base may resume flights as early as Tuesday. 

Although investigators have not found a root cause of pilots reporting symptoms of oxygen deprivation, they have narrowed the potential causes enough to come up with solutions, said Luke Air Force Base Commander Brig. Gen. Brook Leonard on Friday. 

Leonard first halted F-35 flights on June 9 after five pilots in five weeks complained of hypoxia-like symptoms while flying. The pilots, who all flew different jets, landed safely after the backup oxygen system automatically activated, said Maj. Rebecca Heyse, a Luke spokeswoman.


F-35 fighter jets were grounded at Luke Air Force Base in Glendale, Arizona, after some pilots reported hypoxia-like symptoms.

“We have some areas which we think maybe, combined together, could cause physiological incidences, but we’re not sure,” Leonard said.

Based on that, military leaders are putting together “risk mitigation efforts” to return to flying, he said. Some examples include:

  • Requiring more training for pilots related to health situations they may encounter while flying.
  • Having pilots wear more devices that measure biometrics.
  • Stopping flying maneuvers that could cause oxygen-related problems. All five incidents occurred at a certain altitude and cabin pressure, Leonard said. 
  • Protecting the pilot from gases and fumes as they traverse the airfield.
  • Ensuring the emergency backup oxygen systems are at full capacity rather than simply above the required level.

Leonard said that he hopes the mitigation efforts resolve the problem, which he thinks may be caused by a combination of minor factors.  

The commander said flights will resume when he and other staff are confident they’ve identified effective solutions, possibly as early as Tuesday.  

Other F-35 bases did not suspend flights in the wake of the grounding at Luke.

The initial suspension at Luke was supposed to last only one day as leaders reviewed protocols with pilots should they experience hypoxia. But on Monday, Luke officials announced the suspension would continue indefinitely as a team of engineers and maintenance specialists investigated the issue.

Leonard said that of the roughly 86,000 sorties involving the F-35 at Luke since 2014, only 23 reported incidents involved physiological issues. Luke officials discovered the cause of 13 of those incidents. Ten, including the recent five, remain a mystery. 


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