A T-6A Texan II pilot flies in formation with another T-6A. Credit: US Air Force / technical sergeant Jeffrey Allen.

The US Air Force (USAF) has lifted the operational pause issued on the fleet of the T-6 Texan II trainer aircraft following the collection and evaluation of operational flight test data.

Directed by the 19th Air Force commander major general Patrick Doherty, the operational pause, which started on 1 February, was implemented in order to ensure the safety of the aircrew.

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The decision was taken after several unexplained physiological events were experienced by the Air Education and Training Command (AETC) pilots at the Columbus Air Force Base (AFB) in Mississippi, the Vance AFB in Oklahoma, and the Sheppard AFB in Texas.

Occurring over the last two weeks of January, the incidents were claimed to be different from classic hypoxia that is caused by oxygen deprivation.

Doherty said: “The operational pause was required to provide a robust and intrusive look at every component on every aircraft connected to or critical to the On-Board Oxygen Generating System (OBOGS).

“Our intent was to ensure aircrew awareness of UPEs, as well as newly required aerospace physiology training, checklist procedures, and flight equipment modifications that ensure aircrew safety.”

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To investigate on the incidents, Doherty, along with a team of experts from the USAF, the US Navy, Nasa, and medical specialties, collected and evaluated data from the pilots, who had experienced physiological events, and the aircraft.

“The engineers will continue to analyse the data and carry out additional tests to identify the final root cause for improved insights and applications.”

Doherty added: “After listening to pilots, maintainers, engineers, and flight surgeons, it became apparent the T-6 fleet was exhibiting symptoms indicative of a compromise of the integrity of the OBOGS, leading to degradations in performance, which then likely led to the pilots’ physiological events.”

The engineers will continue to analyse the data and carry out additional tests to identify the final root cause for improved insights and applications for future aircraft designs.

With the new evaluations that focus on OBOGS components, the 19th Air Force officials aim to reduce the total number of physiological events in the future.

Following the lift, instructor pilots will be the first ones to resume flying the T-6 Texan II aircraft. They will be followed by students, who are expected to restart flying the jet by the end of the week.