At least nine passengers and flight attendants were swept to their deaths on Friday through a gaping hole torn in the fuselage of a United Airlines jumbo jet on a flight from Honolulu to New Zealand.

United Flight 811 had been airborne for 42 minutes out of Honolulu over the Pacific when the pilots reported problems with two engines. The plane returned to Honolulu International Airport and landed safely, with an 11-by- 20-foot hole above the forward right cargo area. In addition to the dead, 27 people were injured, including four crew members.

The investigation is likely to center on the aircraft's structural integrity and maintenance history. The jet, an early version of the Boeing 747, is almost 19 years old. Although the number of landings and flight hours it has accumulated places the jetliner squarely in middle age, it was modified to update the upper deck from the original three-window configuration to a 10- window configuration.

The possibility of a bomb, as was responsible for the deaths of 270 people on Pan American World Airways 747 in December, has tentatively been ruled out.

As investigators from the National Transportation Safety Board, the Federal Aviation Administration, United and Boeing Co. gathered in Honolulu, the cause of the gaping hole remained a mystery.

"I was awakened by a low, growling, grinding noise, followed by a bang and a flash," said Lynoor Birrell of Wellington, New Zealand, who was sitting with her husband and 4-year-old daughter in Row 13. "I opened my eyes and saw all the overhead baggage racks in our section were gone, as was the overhead TV movie projectors."

Six pairs of seats, in Rows 8-10, were also missing. All had been occupied.

The Honolulu Medical Examiner's Office said later on Friday that "multiple small body fragments and pieces of clothing" were found in one of the right-side engines. Deputy Medical Examiner Mary Flynn said it was not known whether the fragments were from one or more bodies.

"I know there were people in those seats because when we got on the plane, we looked around for places to lie down and stretch out, but the plane was virtually full," Birrell said.

United Flight 811, which originated in San Francisco and made a stop in Los Angeles, took off from Honolulu at 1:34 a.m. (6:34 EST) for a flight to Auckland, New Zealand. At 2:16 a.m., as the plane was climbing at 20,000 feet, the pilots told air traffic controllers that they had lost power in the inboard engine on the right wing, the FAA said.

Eight minutes later, the pilots reported that the outboard engine on the right wing was also losing power and that they would have to shut down the engine and declare an emergency. The plane, powered by its two remaining engines, landed at 2:33 a.m.

The 110-by-110-inch right cargo door broke away during the accident. The hole, which runs vertically up to the roof of the aircraft, is roughly the same width as the door. Just above the door, the tear in the aircraft skin follows straight lines, indicating the hole broke on rivet lines along the jet's skeletal structures.

The FAA issued an order in July requiring inspections and testing of cargo doors on 747s after reports that some doors had partly opened in flight. The FAA warned that a partly opened door could result in a rapid loss of pressure in flight. It was not known whether the United jumbo jet had undergone the inspections.

Investigators said it was not clear when the aircraft's skin broke open. But they said that the engine difficulties reported by the pilots could have been caused by debris from the hole that flew into the engines and clogged them. Such an explanation would be consistent with the configuration of the 747, with its wings sweeping back from the fuselage.

Another possible explanation for the loss of the power in the engines would be a rupture in fuel lines or controls that could have occurred as parts of the aircraft ripped away or that could have resulted from damage caused by flying debris.

The accident was strikingly similar to one last April that also occurred over Hawaii and also involved a structural failure in the skin of an Aloha Airlines jet. In that accident, the top third of an 18-year-old Boeing 737 tore away as the jet cruised at 24,000 feet on an inter-island hop. Although still under inquiry by the NTSB, investigators have concluded that the jet's skin ruptured as a result of metal fatigue, caused in part by corrosion.

The Aloha accident fueled debate between the industry and the government about the safety of aging aircraft. The issue has not been resolved. But researchers are inching toward a consensus that would require mandatory replacement of aircraft sections at various points in an aircraft's life, as opposed to the present method of increased inspections to look for damage or cracking that would prompt replacement.

The hole in the side of the United plane was less dramatic than the Aloha aircraft's. Still, it was "large enough to drive a car through" said Bruce Lampert, a passenger from Denver. As with the Aloha accident, the United passengers reported feeling tremendous gusts of wind and being showered with debris, including insulation, cups, ice and napkins.

THE MISSING: Here is a list of the nine passengers missing from United Flight 811 as provided by United Airlines:

1. Lee Campbell, Wellington, New Zealand.

2. Susan Craig, Morristown, N.J.

3. Harry Craig, Morristown, N.J.

4. Dr. John Michael Crawford, Sydney, Australia.

5. Anthony Fallon, Long Beach, Calif.

6. Barbara Fallon, Long Beach, Calif.

7. Mary T. Handley, Bay City, Mich.

8. Rose Harley, Hackensack, N.J.

9. John Swann, Sydney, Australia.