An F-35A Lightning II on static display at Luke AFB, Arizona, in April 2016.

An F-35A Lightning II on static display at Luke AFB, Arizona, in April 2016. U.S. Air Force / Tech. Sgt. Christopher Boitz

US Air Force Grounds F-35s at Arizona Base

Base officials halted local flights after five pilots experienced symptoms of oxygen deprivation.

The U.S. Air Force has grounded 55 of its F-35 Joint Strike Fighters at Arizona's Luke Air Force base following five incidents in which pilots experienced symptoms of oxygen deprivation.

The pilots “reported physiological incidents while flying” but a backup oxygen system turned on, allowing them to land safely, Capt. Mark Graff, an Air Force spokesman at the Pentagon, said in an email Friday afternoon.

This is the second time Air Force F-35s have been grounded since the service declared they ready for war last summer. The planes were grounded in September due to cracking electrical lines in their fuel tanks.

A battle-ready squadron of F-35s at Hill Air Force Base in Utah, and other jets at Eglin Air Force Base in Florida, Edwards Air Force Base in California and Nellis Air Force Base in Nevada are still cleared to fly. Graff said the planes at Luke should be cleared to resume flights on Monday.

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“Wing officials will educate U.S. and international pilots today on the situation and increase their awareness of hypoxia symptoms,” Graff said. “Pilots will also be briefed on all the incidents that have occurred and the successful actions taken by the pilots to safely recover their aircraft.”

The F-35 program office in Arlington, Virginia, has stood up a “formal action team of engineers, maintainers and aeromedical specialists to examine the incidents to better understand the issue,” Graff said in the statement.

The U.S. Air Force trains F-35 pilots at Luke. Pilots and maintainers from Australia, Norway, Italy, the Netherlands, Japan and Israel are at various training stages at Luke.

The grounding comes amid a series of incidents across the military over the past eight years in which pilots have experienced hypoxia-like symptoms. The most recent incident came in Navy T-45 Goshawk, a jet uses the Navy uses to train pilots. The planes are operating under flight restrictions and must fly at lower altitudes and make slower turns.

Air Force pilots have experienced hypoxia-like symptoms before. There were high-profile grounding of the F-22 Raptor in 2011 after a series of physiological incidents.

Air Force F-35s are still expected to fly to France next week for the Paris Air Show, Graff told Defense One in an email. Those planes will come from Hill Air Force Base.