Air Force: Grounded F-35s at Luke Air Force Base to start flying next week

An F-35 Lightning II prepares to take off June 10, 2016 at Luke Air Force Base, Arizona.


By TARA COPP | STARS AND STRIPES Published: June 16, 2017

Note: This article has been corrected.

WASHINGTON – The Air Force plans to get its F-35s at Luke Air Force Base flying again Tuesday, but with restrictions to prevent more of the oxygen deprivation incidents that led to their grounding, Brig. Gen. Brook Leonard said.

All 55 of the F-35s of the 56th Fighter Wing, which includes 40 U.S. aircraft and 15 aircraft from other countries, were grounded last week at the Arizona base after five pilots in a month reported experiencing hypoxia or similar symptoms during flight. Hypoxia is when an insufficient amount of oxygen reaches the bloodstream and tissue and leads to disorientation, loss of consciousness or death. 

Hypoxia events have also spiked with the Navy’s F/A-18 and T-45 jets, which have led to a grounding of the T-45s. On Thursday, the Navy released an investigation into what could be causing the failures in oxygen delivery to its pilots. That report noted four pilots have died in crashes where hypoxia or related symptoms could have been a factor.

Oxygen system failures have also been reported in some of the Air Force’s F-22 fighter jets.

Neither the Navy nor the Air Force have been able to identify a root cause of the problems. In the Air Force’s case, however, all five of the recent incidents with aircraft at Luke occurred as pilots were flying at approximately the same altitude and interior cabin pressure altitude, which the Air Force would not specify. 

In all three aircraft, oxygen quality and delivery is regulated by an on-board oxygen generation system, or OBOGS.

In the days since Luke announced the F-35 grounding, engineers and program managers have looked at the maintenance and some of the flight performance of the system to identify what’s causing the oxygen failures.

Leonard, who commands the 56th Fighter Wing, said Friday that they still have not determined whether the oxygen system is the cause, definitively.

“We do not think the OBOGS system is … as robust as it can be,” he said, noting the system has met minimum standards and held up in the majority of the F-35s flights. “We are pursuing changes to the OBOGS system we think will make it more robust.” 

Besides the common altitudes at which the hypoxia events occurred, it is possible that temperature could have a role, Leonard said. The system is sensitive to high temperatures and water.

As pilots begin flying F-35s again at Luke next week, Leonard said the base will limit pilots’ exposure to high temperatures on the ramp, the area where all 55 fighters are parked. The Arizona climate and the hot exhaust emitted from jets stored closely together could be a contributing factor, he said. 

Since 2011, there have been 23 reported incidents across the services in which pilots said they experienced hypoxia or related symptoms while flying F-35s. Fifteen of the incidents occurred in the F-35A, which is the Air Force’s version of the jet. Three incidents occurred in the Marine Corps’ F-35B and five occurred in Navy F-35Cs. Leonard said the military has identified a cause in 13 incidents. A cause was not determined in the remaining 10.


Correction: Since 2011, Air Force pilots have reported 15 hypoxia incidents flying F-35s. The number of Air Force hypoxia incidents in F-35s was incorrect in an earlier version of this story.

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