Federal Aviation Administrator Langhorne M. Bond yesterday lifted his 37-day ban on DC10 flights, providing that the jumbo jet's engines support pylon is inspected at extraordinarily short intervals and untimately redesigned.

"We have resolved to my satisfaction the safety questions raised by the tragic crash of [American Airlines] Flight 191 in Chicago, and we have worked out strict measures to assure that such a crash will not occur again," Bond said. The May 25 crash killed 273 and was the nation's worst aviation disaster.

DC10s began flying within two hours of Bond's noon announcement, when United Airlines dispatched a flight from Chicago's O'Hare International Airport to Baltimore-Washington International Airport. Other U.S. airlines flying the DC10 announced varying schedules extending into next week for restoration of full service. There are 138 DC10s in the U.S. fleet. They are operated by eight airlines.

In addition to a rigorous inspection schedule for the engine support pylon, the key component that failed in the Chicago crash, the FAA also required rewiring of some DC10 cockpit warning systems and the regular reinspection of the cables that operate critical flight controls.

Instructions for all of those items were sent to DC10 operators earlier this week, and FAA inspectors have been watching the work on each DC10. About 100 planes had passed inspection yesterday, Bond said, and thus many were ready to resume flying as soon as he gave the orders.

In addition to the new inspection programs, the FAA will require within 15 months the installation in DC10s of a second, totally independent system that would warn either the pilot or the copilot of the kind of control failure that occurred in the Chicago crash.

Changes in maintenance practices on the DC10 have already been ordered because a maintenance procedure was blamed again by Bond yesterday for inflicting the damage on the pylon that caused the crash.

In arriving at these decisions and in permitting the plane to fly again, the FAA has been forced to discover things about itself it would probably just as soon not have known.

Bond ordered extensive investigations into the maintenance procedures used by the airlines, and into the FAA's original approval of the DC10's pylon design control and warning systems.

The FAA is supposed to supervise maintenance, and the procedures have been found waiting. The FAA was supposed to guarantee that the DC10's certification was properly supervised, and it discovered some gaps.

Additionally, the FAA discovered manufacturing deficiencies at McDonnell Douglas, indicating that the quality-control program the FAA is supposed to oversee needs some work.

"There is no question that our maintenance supervision requires a complete review and upgrading," Bond said yesterday. The other problems turned up by his reports will occupy FAA specialists, and Congress, for months.

The new procedures and requirements for the DC10 can be traced directly to things that went wrong on Flight 191.

Just as the plane lifted off the runway at O'Hare International Airport May 25, the engines and its support pylon fell off the left wing. In the process, the hydraulic lines that powered wing control surfaces were severed and an electrical system providing juice for several cockpit warning devices shorted out.

The pilot continued his takeoff because he was beyond the point of no return. From signals in the cockpit he could have known only that his engine under the left wing was not working, not that it had fallen off.

Because the hydraulic lines were gone, the slats on the leading edges of the left wing retracted into the wing. The slats remained extended on the right wing. Slats are huge metal plates that are extended during takeoffs and landings to give a jet extra lift at low speeds.

When that happened, the pilot needed to increase the left-wing lift if he was going to hope to save the plane. He didn't know that, because warning systems that might have told him of the slat condition had gone out with the electricity.

The DC10 continued to climb, as it is perfectly capable of doing with only two of its three engines working, but because there was inadequate lift on the left wing, the plane rolled out of control to the left and crashed. Had the pilot known before the roll started that it was pending, he possibly could have saved the plane, test pilots have demonstrated in a simulator.

What Bond ordered yesterday were actions to:

Make sure the pylon stays on the airplane.

Make sure that if it falls off, the pilot will have enough information to fly out of trouble.

The pylon was designed by McDonnell Douglas and certified by the FAA. When the FAA went back to reexamine that work, it discovered, according to its report, that the original data submitted for certification was deficient for six reasons.

Additional data, received as a result of the investigation, "now show compliance," the report said.

Nonetheless, parts of the DC10 pylon are to be reinspected as frequently as every 100 flight hours - eight to ten days. Other parts, including the aft bulkhead that broke on the crashed airplane, will have to be electronically and visually reinspected every 600 hours. Both of those parts are hard to get and require removing many bolts and fasteners to inspect.

Airline officials said yesterday that the inspection schedule would doubtless increase maintenance cost. Most airlines said it is too early to predict whether the requirement would interfere with DC10 schedules, but National Airlines said it would not.

Because of the difficulty of the reinspection and the "inherent risk that everytime you take apart a complicated piece of machinery you might not put it back together right," the FAA said yesterday, certain pylon elements will need to be redesigned within two years so they will need fewer inspections.

The rewiring of the warning systems and the longer-range requirement for total redundancy in one warning system will insure that the pilot knows what he needs to know, Bond says.

Bond also said yesterday that new cracks had been discovered on six DC10s reinspected this week were not in a critical area. Cracked parts must be replaced before the plane can be flown, he said, and the tough inspection schedule will guarantee that any problems will be caught in time. CAPTION: Picture, Langhorne Bond: "We have resolved to my satisfaction the safety questions . . ." By Joe Heiberger - The Washington Post