A structural failure and not a bomb may have caused the "big bang" that ripped open an Aloha Airlines jet, injuring 61 people and apparently sucking a flight attendant from the cabin to her death, sources said Friday.

The Boeing 737, which was cruising at 24,000 feet on an island hop from Hilo to Honolulu, made a safe emergency landing at Kahului airport Thursday, after flying about 15 minutes with 20 feet of its upper fuselage just behind the front passenger door torn away to the floor. Witnesses said one engine was on fire."There was a big bang when it happened, and everybody looked up and we were looking at blue sky," said passenger Bill Fink of Honolulu.

The possibility of a bomb having exploded aboard the aircraft has been ruled out, said one source in Washington, speaking on condition of anonymity.

The Federal Aviation Administration had ordered a close inspection of the upper skin of older model Boeing 737s including the Aloha jet in October because of cracks near where sections of sheet metal overlap and had warned such cracks could cause rapid cabin decompression, according to FAA officials in Washington.

"We are in full compliance with the October directive," Stephanie Ackerman, an Aloha Airlines spokeswoman, said Friday. She said the inspections have been done as outlined by the FAA and turned up nothing unusual.

FAA records also showed that the Aloha plane had extensive repair work done to mend cracks and corroded metal twice in 1983, but most of that work involved problems with the lower half of the plane, which seemed not to be involved in Thursday's incident.

A source close to the accident probe in Washington said investigators are focusing on whether a structural failure such as metal fatigue or corrosion might have caused the airplane's skin to tear, causing rapid decompression.

One theory is that strong winds may then have ripped away the huge upper section of the fuselage from just behind the front door to within a few feet of the wing, sources said.

Investigators also believe that it is unlikely that an engine failure played a significant part in the plane tearing apart, a source said.

Meanwhile, a Coast Guard cutter and helicopter searched the Pacific Ocean south and southeast of Maui for "anything associated with the explosion of Flight 243," according to spokesman Brad Nelson.

Searchers had been unable to locate flight attendant Clarabelle B. Lansing of Honolulu, a 37-year veteran with the airline, or any debris from the plane, Nelson said.

Aloha officials said they believe Lansing was sucked out of the plane when it rapidly decompressed after the explosion.

Passengers held onto another flight attendant so she would not be sucked out of the open plane, according to passenger Dan Dennin, a Honolulu salesman.

Seven of the injured remained at Maui Memorial Hospital on Friday. One was in critical condition and one in guarded condtion.

George Harvey, Federal Aviation Administration area coordinator for Honolulu, said some National Transportation Safety Board investigators arrived at Kahului Airport on Thursday and would hold a news conference Friday.

Harvey said he could not confirm whether investigators suspected a structural failure caused the fuselage to tear away from the airplane.

"It stands to reason that they're checking everything structure failure, explosive devices," Harvey said.

The plane was carrying 89 passengers, five crew members and an air traffic controller when the explosion occurred around 1:45 p.m. HST. The plane, traveling about 345 miles per hour, was 25 miles southeast of Maui.

"There was a blast . . . a whoosh, like someone popped a bag . . . and the air rushed out immediately," said Dennin. "A third of the roof was gone. . . . I looked up and saw blue sky."