American Airlines and Continental Airlines were permitted under Federal Aviation Administration rules to change the manufacturers' approved maintenance procedures on the DC10 jumbo jet without telling the FAA, officials of the agency told Congress yesterday.

The change in maintenance procedures and the FAA's supervision are critical to understanding the DC10 crash in Chicago May 25 because investigators strongly believe that maintenance played a key role in the accident.

A seven-ton engine and support pylon fell off the left wing just as American Airlines Flight 191 was lifting off the runway at Chicago's O'Hare International Airport. The crash, the worst in U.S. history, killed 273 people.

Investigators believe that improper maintenance procedures could have resulted in damage to the fitting that held the pylon to the wing. They have been careful to state, however, that they do not yet know what part failed first in the crash.

The disclosure that the FAA had no prior knowledge of the change in procedures came during a joint hearing of two House Public Works subcommittes. It was also established for the first time in testimony yesterday that:

Because of the loss of hydraulic fluid, control surfaces called slats on the left wing retracted as the plane was taking off while those on the right wing remained extended. That situation, called asymmetric slats, caused the plane to roll to the left.

The pilot, Captain Walter Lux, never knew the true condition of his airplane based on warning lights and signals available in the cockpit. Had he known that an engine had fallen off the wing, not just that he had lost power, and had he known that the slats were asymmetrical, it is possible he could have saved the aircraft, National Transportation Safety Board office postulated.

One reason the pilot did not know the plane's true condition was because the stall warning - a device that tells the captain when his plane is going too slowly to maintain flight, was made inoperative by an electrical failure. The same electrical failure cut off the cockpit voice recorder just as the plane's nose lifted off the ground. The last word recorded was "damn."

Investigators now believe that when the engine and pylon left the wing they took with them hydraulics controls for the left wing and the electrical power for the stall warning.

Also yesterday, John Brizendine, president of the Douglas Aircraft Co., a division of McDonnell Douglas Corp., said in a statement prepared for delivery that "we believe firmly" that the grounding of the DC10 "was unnecessary to assure the safe operation of the DC10 fleet." Douglas is the manufacturer of the plane.

Brizendine will deliver his prepared testimony and answer questions this morning.

Federal Aviation Administrator Langhorne M. Bond ordered all U.S. DC10s grounded on June 6 and they have remained so since. Bond said there was a "possible design problem" and that questions about maintenance had to be answered before the planes would be permitted to fly again.

At first, all foreign aviation authorities controlling DC10s followed suit. Yesterday, however, aviation authorities in France, Britain, the Netherlands, Switzerland and Indonesia permitted their DC10s to resume operations. But those planes are forbidden by U.S. regulations from flying in the United States.

The maintenance procedure in question involves the engine and pylon mounting system. McDonnell Douglas, in its recommeded maintenance manual, said the engine and pylon should be removed from the wing separately, then reinstalled separately, when maintenance in that area was required.

However, both American and Continental chose to remove and install them as a single unit, a practice prohibited by the FAA since the Chicago crash. In that maintenance operation, investigators believe, it is easy to crack one of the key engine mounting points. Such a crack was found on the crashed airplane in Chicago.


DURING A RECESS IN THE HEARING, CLARK ONSTAD, FAA's chief counsel, called John Cyrocki, a retired FAA employe who is heading a special maintenance investigation, and asked him.

"Mr. Cyrocki told me," Onstad said, "that both American Airlines and Continental manuals state that they are to use the Douglas [maintenance] procedure unless a company procedure supersedes the recommended Douglas procedure." The FAA approves those manuals.

Superseding company procedures, Onstad said, were implemented through devices known as "engineering change orders." A change order, Onstad said, "was not submitted to the FAA."

Airlines are required to tell the FAA if they make a major change in the maintenance procedure, the FAA's John Bartel said.

Rep. Jerome Ambro (D.N.Y.) asked, "Then the airlines determine whether it is major or minor?"

"That is correct," Bartel said.

Bond said that "our system did not pick it up. I want to assure you that we will cure that difficulty."

Earlier in the hearing, safety board officials gave the clearest explanation yet made public of exactly what happened to Flight 191. The problems of the asymmetrical slats and of the missing stall warning were developed in questioning by Rep. Norman Y. Mineta (D-Calif.).

William Hendricks, chief of aviation investigations for the board, was asked by Rep. Elliott H. Levitas (D-Ga.) if the pilot could have done anything to save the airplane if he had known exactly what was wrong with it.

"It's a bit premature to speculate," said Hendricks. "But had he lowered his pitch attitude [the angle of climb] and built up some speed, there would have been some changes."

"What if he was able to build up speed? Levitas asked.

"He probably would have had controllability over the roll movement of the aircraft," Hendricks said.

Flight 191 took off with two of its three engines, climbed routinely for about 18 seconds, rolled suddenly to the west as the slats on the left wing retracted, and then fell to the ground.