The Air Force grounded all T-38C training jets on Thursday, following the second fatal crash involving the aircraft in eight days, the military said.

Two pilots died when their high-altitude, supersonic plane went down during a routine training mission, according a statement from Sheppard Air Force Base.

The two-seat plane was assigned to the 80th Flying Training Wing, a multinational organization that produces future combat pilots for NATO. The names of the airmen were not immediately released.

The crash follows the deaths of two pilots whose training jet crashed April 23 at Columbus Air Force Base in Mississippi.

"At this point we have no indication that there was any tie between the two," said Capt. John Severns, Chief of Media Relations for Air Education Training Command at Randolph Air Force Base near San Antonio.

The Air Force suspended all T-38 flights pending the investigations into what caused the two planes to go down. The jets are used to prepare student pilots to fly fighters and bombers.

"Until we have more complete understanding of the causes of both accidents, it's prudent to stand down the T-38s" said General William R. Looney III, the commander who issued the order.

The Air Force has about 500 of the aircraft in its inventory.

First deployed in 1959, the jet has been linked to 138 fatalities and some 189 crashes, according to the Air Force Safety Center.

Of 16 fatalities related to crashes at Sheppard Air Force Base since 1967, all but six involved T-38s.

Pilots from 13 NATO countries train through Sheppard's Euro-NATO Joint Jet Pilot Training Program.

The T-38's crew normally consists of a student pilot and instructor seated in tandem. Student pilots learn aerobatics, formation flying, night and instrument flying, cross-country awareness, general maintenance awareness and supersonic techniques.

All Thursday flights at Wichita Falls' Municipal Airport, which shares runways with Sheppard, were canceled.

Wichita Falls is about 135 miles northwest of Dallas.