The Boeing 747-100 jetliner that lost a cargo door, a slab of fuselage and nine of the people aboard after takeoff Friday from Honolulu was the oldest jumbo jet still in the United Airlines fleet.

Federal Aviation Administration records reveal a history of structural problems that were discovered and repaired on the aircraft, though they were not considered out of the ordinary for a plane in use so long.

In addition to looking at the possibility of metal fatigue in the 18-year-old aircraft, investigators were exploring whether a faulty or improperly closed cargo door may have been involved.

The 100 series was the original model of the Boeing 747, and 205 were manufactured between 1969 and 1976.

The aircraft in question was the sixth Boeing 747 delivered to United Airlines, arriving Nov. 3, 1970. It was the 89th jumbo jet to come off the assembly line at Boeing's Everett, Wash., plant.

Since then it has flown nearly 58,000 hours and made about 15,000 "cycles" - with each cycle being a takeoff, cabin pressurization, depressurization and landing.