Vance Air Force Base confirmed Friday it has temporarily pulled its T-6 Texan II training aircraft from flight operations.
In a press release, the base said the 71st Flying Training Wing's more-than 100 T-6 aircraft were placed on an "operational pause" after several "physiological incidents" in the aircraft.
The press release stated the action was taken Wednesday "after a fourth physiological event occurred since Nov. 1."
According to base officials, four instructor pilots and one student pilot assigned to Vance have reported physiological incidents while flying this month.
"In each case, the aircraft's backup oxygen system operated as designed, and the pilot followed the correct procedures, landing the aircraft safely," the press release stated.
The press release did not specify the nature of the physiological incidents, and Vance Public Affairs said further details were not available Friday.
"Vance Air Force Base is committed to ensuring aircrew safety is paramount, and are conducting a full investigation of the reported cases," said Col. Darrell Judy, 71st Flying Training Wing commander, in the press release.
Base officials are using the "operational pause" to implement a program "to brief instructor pilots and students on the situation and increase their awareness of physiological incidents," the press release stated. "Pilots were also briefed on all the incidents that have occurred and the successful actions taken by the pilots to safely recover their aircraft."
"Flight medicine briefed physiological event symptoms and also the extensive measures that are being taken to analyze data collected from the incidents," the press release stated. "Additionally, the 71st Operations Group held an open forum to discuss any concerns pilots may have given these recent occurrences."
Currently, the local flying operational pause is limited to Vance Air Force Base T-6 Texans. Because the incidents are limited to the T-6 airframe, T-1 Jayhawk and T-38 Talon flight operations will continue.
"Air Force senior leaders are aware of the incidents and are actively providing support and resources as necessary," the press release stated.
This is not the first time T-6 aircraft have been pulled from flight operations at Vance.
In April 2015, T-6 training planes at Vance were grounded for a week after an in-flight engine failure apparently caused by an engine oil line malfunction. That led to the entire fleet of 445 T-6s in Air Education and Training Command being temporarily grounded for inspection.
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.