Federal investigators are flying part of the cargo door lock of a crippled United Airlines Boeing 747 to Washington for examination to try to find out what caused a gaping hole to burst open on the plane, hurling nine people to their deaths over the Pacific Ocean.

"We're focusing on the cargo door area, and one of the areas that we're looking at is the latching mechanism," Lee Dickinson of the National Transportation Safety Board told reporters in a briefing Sunday night.United Airlines ordered new checks Sunday of cargo doors on its Boeing 747s as 70 to 100 federal investigators in Honolulu tried to narrow the possible causes of the accident early Friday.

The 10-by-20-foot hole ripped open around a cargo door as Flight 811 was 100 miles south-southwest of Honolulu, 17 minutes into the flight carrying 354 people to Auckland, New Zealand.

The 10-foot-square cargo door is secured by two hooks on the sides and eight latches on the bottom, Dickinson said. The door is shut electronically and a handle on the outside is used to lock it tightly.

All of the moving parts of the locking mechanism were on the cargo door, which has not been found, Dickinson said.

There were score marks but no other breaks or abnormalities on the eight lower latch pins, but authorities did not know whether latch pins on undamaged aircraft are scored in the same way during normal use.

One of the latch supports was removed and will be flown to Washington for metallurgical analysis, Dickinson said.

"We will be looking at other 747 airplanes to see what those airplanes look like and be comparing latches with other airplanes," he said.

Dickinson said the analysis might tell investigators whether the latches broke or were left unlatched.

In Chicago, United Chairman Stephen M. Wolf said cargo doors on all 31 United 747 jumbo jets will be re-inspected upon every landing. Mechanics will supervise baggage loaders to make sure the doors are properly closed and locked before takeoff, he said.

"In announcing these steps, we want to make clear that we are not speculating and will not speculate on the cause of Friday's incident," he said.

Investigators Sunday interviewed the ramp supervisor and other ground personnel who opened and closed the door and loaded baggage onto the plane before the accident early Friday.

"They confirm that the cargo door was latched," Dickinson said.

A warning light in the cockpit was tied into two pressure release doors on the cargo door, and any movement of the cargo door should cause the light to come on, Dickinson said. Investigators ran tests on the system, and "everything checked out fine."

Technical personnel from the safety board and Boeing were to look Monday into such areas as what kind of fail-safe system the plane's design includes in the event the cargo door is lost.

Since there is no evidence of a bomb, the FBI and Federal Aviation Administration investigators have finished their part of the probe, Dickinson said.