The National Transportation Safety Board officially concluded its investigation into the nation's worst airline disaster yesterday with a strong attack on the Federal Aviation Administration's stewardship of aircraft manufacturing and surveillance of airline operations.

In its finding of "probable cause" of the May 25 American Airlines DC10 crash in Chicago that killed 273 people, the board placed much of the blame on the airline, and attached somewhat less to DC10 manufacturer McDonnell Douglas and to the FAA.

However, the board then adopted eight specific recommendations to the FAA that cover the range of FAA responsibilities from approving the birth of an airplane to establishing appropriate maintenance procedures and piloting techniques to guaranteeing that problems, once discovered, are made known throughout the industry so they do not recur.

Among other things, the board recommended that the FAA:

Require, during the time it is officially certifying a new airplane, that ease of maintenance and ability to survive a combination of possible problems be considered. The DC10 crash has been traced to maintainance-induced damage, the board said. Further, the Faa's certification process did not consider the possibility of the multiple system failures that occurred in the Chicago crash.

Require that large airplanes be designed either to prevent the occurrence of an inbalance in the high-lift devices on the wings or to provide a completely redundant warning system for the pilot. In the Chicago crash, the loss of hydraulic fluid in the left wing caused its high-lift slats to retract while they remained extended on the right wing. The pilot did not know this, however, because his warning system was rendered inoperative at the same time the hydraulic system was damaged.

Conduct "strict and comprehensive surveillance" of quality control by the manufacturer. Post-crash examination of other DC10s found at least two kinds of quality-control problems in the manufacture of the engine-support pylon, the part that ripped off the wing of the crashed airplane.

Require that an airline do a "hazard analysis" when it is going to perform maintenance work in a way other than that prescribed by the manufacturer. No such analysis was performed by American Airlines, the board said, and the airline's maintenance procedure is blamed for inducing the crack that led to the break that caused the pylon to fall off the wing.

Require airlines to report to the FAA structural damage to an airplane that occurs during maintenance. Today, such reporting is apparently expected only for in-flight damage. Before the Chicago crash, other DC10 pylons were damaged during maintenance and went unreported.

Revise airline operating procedures to provide added margins of safety during takeoffs. Is is generally agreed that if the pilot of American Airlines Flight 191 had concentrated on going faster rather than climbing higher he could have saved the plane. However, he was flying the plane exactly the way he had been taught to fly it with one engine not operating. The only damage he could have known about for sure was that one engine was not operating. In fact, the engine and its pylon were gone (they fell off just after takeoff) and the plane's life blood -- hydraulic fluid -- was leaking through the rupture. Since the accident, American Airlines and some other DC10 operators have changed their "engine-out" takeoff procedures to favor speed over altitude.

The FAA has already taken some of the actions proposed by the safety board and will consider the others, according to a spokesman. The board can only recommend changes; it cannot force the FAA to comply.

The board's official ruling of probable cause, highly technical in nature, says the accident happened because of the "uncommanded retraction of the left wing outboard leading edge slats" and the loss of warning systems to the pilot. Those losses resulted, the board said, from "maintenance-induced damage."

Contributing factors included "the vulnerability of the design of the pylon attach points to maintenance damage, the vulnerability of design of the leading edge slat system to the damage," plus deficiencies in the FAA system by which maintenance problems and reports should be shared throughout the industry. Alson cited as contributing was "the intolerance of prescribed operational procedures to this unique emergency." Board members made clear several times during their discussions that the crew of the DC10 was blameless.

Responding yesterday, American Airlines senior vice president Donald Lloyd-Jones said "we do not agree with the emphasis on maintenance-induced damage" as part of the probable cause. He said the board's findings should have included an explanation of the length of the crack in the pylon that ultimately led to its failure. That crack, maintenance-induced, the board said, grew to a fatal 13 inches under the stress of flight.

American has contended since early in the accident investigation that a shim -- a thin strip of metal used to close a gap during manufacturing -- contributed to the length of the crack. McDonnell Douglas has contended that the shim -- a nonstandard item in the production drawings -- would strengthen the pylon, not weaken it. Both sides have produced a blizzard of technical data supporting their positions.

William Gross, McDonnell Douglas vice president, said "we agree with the board's recommendations regarding improvements in communication within the industry." He would not comment on the relative apportionment of blame, but McDonnell Douglas executives and lawyers were clearly happier than American's yestereday.

Lloyd-Jones also said American has undertaken 14 modifications on its DC10s, including rerouting some hydraulic lines to make them less vulnerable and installing locks to make it impossible for wing slate to retract without a specific command from the cockpit. The alterations must be approved by the FAA.

By law, the safety board's findings cannot be admitted as evidence in the mass of post-crash legal proceedings. However, the safety board investigation, including its public hearings and the mass of reports the board has produced, are valuable to attorneys building discovery lists. Every major aviation crash litigation firm had at least one representative wander through the board's two-week public hearing in Chicago in late July.