T-6A Texan II

A T-6A Texan II taxies onto the flight line at Vance Air Force Base in 2012.

(File Photo by BONNIE VCULEK)

VANCE AIR FORCE BASE, Okla. — Vance Air Force Base T-6 Texan II aircraft and their crews will return to the air today, base officials confirmed this morning.

Vance placed its fleet of more than 100 T-6 aircraft on an "operational pause" Nov. 15, 2017, after five aircrew members reported symptoms similar to hypoxia, or oxygen deprivation, during four separate incidents, according to press releases provided to the News & Eagle.

A two-week investigation into the aircraft's oxygen system ensued, drawing in resources from Air Education and Training Command, airframe and component manufacturers and other Air Force commands.

71st Flying Training Wing officials said Monday the cause of the hypoxia-like symptoms experienced in November was not identified during that investigation, but several possible causes were eliminated.

VANCE AIR FORCE BASE, Okla. — Officials with the 71st Flying Training Wing confirmed Sunday they are conducting a limited number of T-6 Texan II test flights as part of an ongoing investigation into possible issues with the aircraft's in-flight oxygen system.

"No specific root cause for the physiological events was identified during two weeks of investigation by aviation, medical, functional and industry experts," said a wing press release. "However, specific concerns were eliminated as possible causes including maintenance and aircrew flight equipment procedures.

"As technical and human performance data continues to be gathered, the Vance team will temporarily apply local procedures to mitigate risk to flight operations and aircrew," the press release stated.

71st Flying Training Wing commander Col. Darrell Judy praised the investigation team for their efforts.

"The cross functional cooperation between agencies spanning the Department of Defense and industry has been outstanding," Judy said. "We are actively using lessons learned across the aeronautics enterprise to determine the cause of these events and are confident implementing mitigation techniques will enable us to return to our primary mission of training the world's finest aviators."

Background to T-6 investigation

According to base officials, four instructor pilots and one student pilot assigned to Vance reported physiological incidents while flying between Nov. 1-15.

Lt. Col. Eric Schmidt, Vance chief of safety, said the aircrew experienced "hypoxia-like symptoms in the airframe that caused the concern that what they felt was beyond the realm of normal operations."

Hypoxia is a condition in which the body is not receiving sufficient oxygen.

Schmidt said none of the aircrew lost consciousness, and in each case they were able to switch over to the aircraft's backup oxygen system, which operated as designed, and were able to safely land the aircraft.

According to Air Force safety protocol each aircrew member was met by medical personnel on the flight line, evaluated and released without any indications of long-term adverse effects, Schmidt said.

The T-6 flight stand-down was limited to Vance Air Force Base. Because the incidents were limited to the T-6 airframe, T-1 Jayhawk and T-38 Talon flight operations were not impacted.

The T-6 is the primary trainer used at Vance and other undergraduate pilot training bases for the Air Force, Navy, Marine Corps and Coast Guard — Columbus AFB, Miss.; Laughlin, Randolph and Sheppard AFB and Corpus Christi Naval Air Station, all in Texas; and NAS Whiting Field in Florida.

The T-6 is a single-engine, two-seat turboprop aircraft manufactured by Raytheon Aircraft Co. The T-6 first was put into use as the Air Force’s primary trainer in 2000, at a cost of nearly $4.3 million per aircraft. The first T-6 arrived at Vance in March 2005.

Student pilots typically spend about 22 weeks going through 90 hours of flight training instruction in the T-6 before moving on to continue training in either the T-38 or T-1.

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Neal is health, military affairs and religion reporter and columnist for the Enid News & Eagle. Follow him on Twitter, @jamesnealwriter, and online at jamesrneal.com. He can be reached at jneal@enidnews.com.

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