The Federal Aviation Administration has ordered airlines flying Boeing 747 jumbo jets to inspect the tail sections of the aircraft and report all findings.

The order, described by the FAA as routine, is one of the follow-up actions that resulted from the investigation of the Japan Air Lines 747 crash Aug. 12 that killed 520 people.

An FAA official said that an earlier request for information to the airlines had not produced the volume of data the agency wants, "so we made the request mandatory."

The rear wall of the cabin of the JAL plane is believed to have failed under pressure, with the escaping pressurized air possibly damaging the tail section. The investigation is continuing.

Inspections of other 747s have found corrosion on bolts connecting the tail fin to the body section. Boeing has recommended replacing those bolts with a more corrosion-resistant version during regular maintenance and inspection.

Boeing also said in a letter to Japan Air Lines that it has modified its 747s to provide a cover over a maintenance access hole between the rear cabin wall and the vertical tail. The cover "will seal an entry hole in the tail fin so, in the unlikely event of a rear wall rupture, it will prevent air from pressurizing" the vertical tail, Boeing spokesman John Wheeler said.

Wheeler said it has not been established that escaping air pressurized the tail fin. But it is known from photographs of the crippled plane that a large section of the tail fin was missing while it was still flying.

The rear cabin wall on the crashed plane, known as the aft pressure bulkhead, was damaged in 1978 during a "hard landing." Boeing repaired the damage. However, the company said in an official statement, "a relatively small section of the bulkhead splice . . . was not correctly assembled during a repair which Boeing made."

Since then, the FAA and Boeing have been studying pressure bulkhead strengths and repair histories.