The U.S. Air Force, which grounded its fleet of T-6A trainer aircraft almost four weeks ago due to a rise in physiological episodes (PEs), announced Feb. 27 that the planes are now cleared to return to flight.

The Air Force said it has determined that the PE surge was caused by the unexpected degradation or failure of a “handful of components” in the plane’s pilot breathing system, also known as the on-board oxygen generation system (OBOGS). Those components will now be replaced or repaired more frequently. 

The T-6A Texan II trainer. (U.S. Air Force photo)
The T-6A Texan II trainer. (U.S. Air Force photo)

“Proactive maintenance mitigation practices and inspections based on flight hours have been created and are being accomplished on a much more aggressive timeline to ensure high performance of the OBOGS,” said Maj. Gen. Patrick Doherty, commander of the 19th Air Force.

Instructor pilots will resume flying first. Students are expected to be back in the air by week’s end.

The Air Force said it worked with experts from the Navy and NASA to pinpoint the cause of the PE surge.

The Air Force grounded its 444 T-6As on Feb. 1 after 10 physiological events occurred at three bases in January (Defense Daily, Feb. 1). On Feb. 6, a service official told a congressional panel that the Air Force was investigating whether maintenance problems with the OBOGS were causing the PEs (Defense Daily, Feb. 8).