WASHINGTON — F-35 flight operations at Luke Air Force Base, Arizona, will continue to be suspended as analysts investigate five incidents where pilots suffered hypoxia-like symptoms, a spokeswoman for the base said Monday.

Since May 2, five 56th Fighter Wing pilots have reported symptoms of oxygen deprivation while flying the U.S. Air Force version of the joint strike fighter, including two incidents that occurred last week. In all cases, the backup oxygen systems kicked in and pilots were able to safely land the plane, but training has ground to a halt to allow a team from the F-35 Joint Program Office, or JPO, to study the events.

Maj. Rebecca Heyse, spokeswoman for the 56th Fighter Wing, said a JPO team of engineers, maintainers and aeromedical specialists arrived on base Sunday and are currently narrowing down potential causes for the incidents. The hope is to identify the root cause over the next couple days, but no date has been set as this time for a tentative resumption of operations, she told Defense News.

"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," she 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.

"Updates will be provided as our teams work together toward safely returning to building the future of airpower through trained F-35A pilots. The safety of our airmen is paramount and we will take as much time as necessary to ensure their safety."

In the meantime, Heyse said the 56th Fighter Wing is continuing a variety of pilot education measures, including an all-call meeting with the JPO team to discuss the events. Cancellation of flight operations affects 49 pilots and 55 aircraft total.

At this point, little is known about the incidents themselves, including whether the On-Board Oxygen Generating System failed in any of the cases. All five events occurred with different jets from multiple squadrons and production batches, Heyse confirmed. However, because only pilots from Luke AFB have developed hypoxia-like symptoms, the service continues to believe it remains a localized problem.

Brig. Gen. Brook Leonard, commander of the 56th Fighter Wing, will make the final call on when to resume flight operations.