The U.S. Air Force has grounded the Beechcraft T-6 Texan II training aircraft at Vance AFB, Oklahoma, after five pilots reported physiological episodes with hypoxia-like symptoms while flying.
The Air Force’s 71st Flying Training Wing enacted an “operational pause” of T-6 flying operations on Nov. 15 after four T-6 instructor pilots and one student pilot assigned to Vance reported physiological incidents since Nov. 1, spokeswoman Terri Schaefer told Aviation Week Nov. 29. 
In each case, the aircraft’s backup oxygen system operated as designed and the pilots followed the correct procedures, landing safely, Schaefer said.
The Air Force is investigating the incidents at Vance and has not yet identified a specific root cause, Schaefer said. The events were reported as “physiological events with hypoxia-like symptoms,” she noted.
The Air Force uses the single-engine T-6 turboprop as a basic trainer for all student pilots. From the T-6, students choose one of three advanced training tracks based on their class standing. Future fighter/bomber pilots next train in the T-38 Talon; pilots on the airlift/tanker track fly the T-1A Jayhawk; and helicopter/tilt-rotor trainees fly the TH-1H Huey.
In addition to Vance, student pilots also train in the T-6 at Randolph AFB, Texas; Moody AFB, Georgia; Columbus AFB, Mississippi; Laughlin AFB, Texas; and Sheppard AFB, Texas.
Since the grounding, Vance AFB has partnered with Air Education and Training Command, 19th Air Force and medical, functional and industry experts to determine the cause of the incidents. That effort has included reviewing procedures for physiological events, providing refresher physiological training, background briefs and Q&A with T-6 instructor pilots, Schaefer said. 
“Following the operational pause, we anticipate that flying operations at Vance Air Force Base will continue as usual, with added awareness and training concerning physiological events and the life-support equipment onboard the T-6 designed to protect pilot safety and ensure continued safety of flight,” Schaefer said.
The T-6 incidents come as a spate of hypoxia-like cockpit incidents plague the Air Force and U.S. Navy fleets. Both the Air Force and Navy grounded fleets this year: the Navy’s T-45 Goshawk trainers and the Air Force’s F-35As at Luke AFB, Arizona, the service’s premier F-35 training base. Similar incidents are also on the rise in the Navy’s F/A-18Hornet and EA-18G Growler fleets.