Updated

The U.S. Navy continues to ground a fleet of training jets because of a spike in problems with their oxygen breathing systems.

Vice Admiral Mike Shoemaker wrote in a Navy blog post Sunday that instructor pilots have raised concerns over potential "physiological episodes" in the cockpit.

The Navy first paused operations of the T-45C Goshawk last week because of contamination in some planes' oxygen systems. The two-seat jet is used to train fighter pilots in the Navy and Marine Corps.

Shoemaker wrote that the grounding will last for at least a week as engineers continue to dig into the problem.

Shoemaker wrote that he spoke with instructor pilots, students and staff at naval air stations in Mississippi, Texas and Florida.