The Strategic Air Command has grounded all 97 of its B-1B bombers because of recurring engine failures.

"SAC Commander-in-Chief Gen. John T. Chain Jr. today grounded the command's B-1B fleet after two B-1Bs experienced catastrophic engine failures within a three-month period," SAC said Wednesday.The command said it would return the bombers to full flying status as soon as possible. No B-1Bs are based at Offutt, where SAC's headquarters is located.

Wednesday's action marks the fifth time in less than two years that the bomber fleet has been grounded.

Chain ordered the planes grounded after a B-1B engine failed Wednesday while flying near Dyess Air Force Base, Texas.

On Oct. 4, an engine on a B-1B from McConnell Air Force Base, Kan., failed while the bomber was flying over southeastern Colorado.

In both cases, the airplanes landed safely and no one was injured. B-1Bs have four engines.

SAC said it suspects fan blades at the front of the engines were to blame for the failures. After the October incident, SAC spokesmen said the fan's failure caused the rest of the engine to be destroyed.

The grounding means that B-1Bs will be flown for no reason other than war. The bombers will remain on nuclear alert at U.S. air bases, ready to launch if superpower tensions reach a crisis point.

B-1Bs have been certified for use in conventional bombing missions, but SAC still has not trained the bombers' crews for anything other than its strategic nuclear mission.

SAC used the word "grounding" in announcing the Wednesday's action, which is unusual. In most cases the command says troubled planes have been ordered to "stand down" until all planes can be inspected.

A "stand down" is a more temporary step than grounding, SAC spokesmen have said in the past.

B-1Bs are permanently based at Ellsworth Air Force Base, S.D., Grand Forks Air Force Base, N.D., Dyess and McConnell.