The U.S. Air Force will continue a temporary suspension of all F-35 flights at Luke Air Force Base in Arizona until further notice, the service said on Monday.
The move comes days after officials halted operations for all F-35A -- the Air Force's model designed for taking off and landing on conventional runways -- at the base after pilots complained of hypoxia-related issues.
"The 56th Fighter Wing will continue their pause in local F-35A flying to coordinate analysis and communication between pilots, maintainers, medical professionals and a team of military and industry experts," Luke spokeswoman Maj. Rebecca Heyse said in a statement.
"This coordination will include technical analysis of the physiological incidents to date and discussions on possible risk mitigation options to enable a return to flying operations," she added. "Updates will be provided as our teams work together toward safely returning to building the future of airpower through trained F-35A pilots."
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Heyse added, "The safety of our Airmen is paramount and we will take as much time as necessary to ensure their safety."
The cause of the setback has not yet been identified, Capt. Mark Graff told Military.com in a phone call Monday. He reiterated the incidents are only "limited to Luke" at this time, meaning other bases aren't affected by the order.
Flying operations were originally set to resume Monday. Brig. Gen. Brook Leonard, commander of the 56th Fighter Wing commander, will decide when the F-35s will return to flight at the installation, officials said.
Graff said last week that the 56th Fighter Wing at Luke canceled local flying operations "due to a series of five incidents in which pilots have experienced hypoxia-like symptoms."
Since May 2, five F-35A pilots have experienced physiological incidents while flying. In each case, the aircraft's backup oxygen system kicked in and the pilot followed the correct procedures to land safely.
A total of 55 F-35As are assigned to Luke.
Base officials educated pilots on the effects of hypoxia on Friday, Graff said. Now, there will be "continued analysis of the incidents, and [officials will] fuse that with more information as they go about it," he said. "The incidents are the crux of the issue," he said.
There have not been additional reports from pilots suffering similar symptoms, Graff said.
The issue of military pilots suffering hypoxia-like symptoms -- shortness of breath, confusion, wheezing -- in-flight isn't limited to the F-35 fleet.
Pilots flying the F-22 Raptor fifth-generation stealth jet experienced hypoxia symptoms on various occasions between 2008 and 2012. One pilot died as a result, and one had a near-death scare, with dozens more pilots experiencing confusion and disorientation while flying, according to an ABC News investigation at the time.
Then-Pentagon spokesman George Little said investigators found the cause to be a faulty valve in the high-pressure vest worn by the pilots at extreme altitude, which was restricting their ability to breathe.
More recently, the Navy went so far as to equip the aircraft carrier USS George H. W. Bush with specialized equipment called a transportable recompression system, or hyperbaric chamber, amid a review of physiological episodes affecting pilots who flew the T-45 trainer and the F/A-18 Hornet.
