A tape released yesterday of the final cockpit conversations on a Midwest Express flight that crashed moments after taking off from Milwaukee on Sept. 6 indicates that neither the pilot nor the copilot had any idea what was happening when the right engine of the McDonnell Douglas DC9 broke apart.

Had they been aware, they might have been able to save the plane with swift action, according to federal aviation officials.

"The question you have to ask at this point is were they so preoccupied with what happened to the engine that they forgot to fly the airplane?" said one official familiar with details of the crash, which killed 31 people. "As far as we know, the plane should have been able to stay in the air."

Federal Aviation Administration regulations require that commercial planes such as the DC9 be capable of flying -- and even of climbing -- with one engine in operation.

But 15 seconds after a sound that the federal inspectors say was probably the right engine shutting down, the plane smashed into a field near the runway at General Mitchell Field.

"What the expletive was that?" the pilot said immediately after he heard a loud clunk, which NTSB officials said was probably made by parts of the right engine breaking apart. "Whatta we got here, Bill?"

The tape, and other documents released by the National Transportation Safety Board yesterday, show that although the right engine failed the left engine should have been able to keep the plane aloft.

The transcripts released yesterday indicated that a stick shaker, which makes a sound that warns the crew that the plane is about to lose the angle necessary to fly, was working properly and should have helped the pilot set the flight right, according to aviation officials. But no action was taken.

The NTSB documents showed that an insufficient amount of air was passing through the left engine when it stalled. The problem, NTSB officials said, was probably caused by the severe angle of the engine as it headed to the ground.

Seconds before the crash, the pilot had radioed the airport traffic control tower, saying that he had an emergency, but he was unable to describe it further.

Witnesses reported that the plane appeared to "hover" and then drop to the ground.

The JT8D engines were manufactured by Pratt & Whitney, a division of United Technologies Corp. They are the world's most widely used jet engine, making about 8 million takeoffs a year.