F-35 fighter jets are still grounded at Luke Air Force Base in Glendale.

U.S. Air Force officials had planned to resume operations Monday after halting operations last week.

Pilots had reported symptoms related to oxygen deprivation. No one was hurt in the incidents that started in May, and the F-35’s backup oxygen worked as designed.

The Air Force continues to meet with pilots and gather information about what happened.

The F-35s have not been grounded indefinitely, according to officials at Luke Air Force Base. But there are still too many unknowns to say when operations might resume. The cancellation has had little impact so far, but it could eventually affect pilot training classes.