As the huge U.S. Army CH47 Chinook helicopter began to climb, the 38 German, French and British parachutists wedged aboard contemplated their mission. From 12,700 feet they would jump, fall free for several thousand feet, pull their rip cords and drift to the airfield.

The Chinook reached 10,600 feet. But then, "We had some noise in the aft and got a flicker on the master caution panel," pilot Leon E. Schoenborn, an Army warrant officer, radioed. There was no particular alarm in his voice, but he began a slow, precautionary descent. As the craft circled down to 1,000 feet, the forward and rear rotor blades suddenly struck each other. The aft rotor assembly sheared violently away.

All 46 persons on board -- the parachutists, the four Army crew members and four other Americans -- were killed.

That 1982 accident in Mannheim, West Germany, and a series of crashes on another model of Army helicopter have resulted in at least 269 deaths in recent years. There is a growing body of thought that they have not occurred only for the reason traditionally given: that Army pilots fly closer "to the edge of the envelope" than civilian pilots.

Rather, judges and juries are beginning to enter large product liability judgments against the makers of military aircraft on grounds the vehicles they sell the Pentagon are defective -- not as safe as they ought to be.

Those legal victories are coming as military safety-consciousness is increasingly becoming an issue in Washington. Is training for the all-volunteer service as safe as it should be? Is there appropriate protection for the investment in training a soldier?

Most people do not strap on parachutes and jump out of airplanes; civilian helicopters do not fly "nap of the earth," hugging the ground to avoid radar, and civilian jets do not soar wing tip to wing tip at twice the speed of sound or try to land on the deck of an aircraft carrier. Despite the dangers, those are realistic requirements of war.

If something goes wrong, the law does not permit the survivors of military personnel to sue the federal government and ask in court whether the military exercised an appropriate standard of care.

Thus, the manufacturers of military equipment have become legal targets. Their standard defense is that they build only what the government tells them to build, and, therefore, they are blameless.

"It is a difficult question in any advanced society making products as we do," said a Defense Department specialist who spoke on background. "If the products don't work right and people get hurt, there is a price to be borne . . . . We haven't as a nation come to terribly well thought-out ideas of who should bear the costs."

A result of that uncertainty is pressure on the military to improve the safety of its equipment and procedures or watch the costs of new products rise as manufacturers hedge against liability losses by jacking up the purchase price.

The costs of military aviation accidents are high. From 1979 through 1984, there were 1,238 noncombat fatalities in Army, Navy, Air Force and Marine Corps aviation accidents, Defense Department statistics show. More than 1,184 aircraft were destroyed at a cost exceeding $4.9 billion.

In 1984, the Army had 30 aviation fatalities, lost 39 aircraft and had an accident cost of $45.6 million.

That year, for every 100,000 hours of flying time, the Defense Department had 2.4 noncombat aviation accidents involving major damage, serious injury or a fatality, its statistics show. Major airlines had 0.164; commuter airlines 1.2, according to the National Transportation Safety Board.

The stories of two Army helicopter models which represent more than half the Army fleet of 7,306, illustrate the safety issues.

At Mannheim the Boeing Vertol CH47 Chinook accident occurred Sept. 11, 1982, during an air show organized for the city's 375th anniversary.

The Army temporarily grounded its fleet of 442 Chinook helicopters while investigators tried to figure out what happened.

The CH47, manufactured in Philadelphia by a Boeing Co. subsidiary, Boeing Vertol, is unusual in that it has two main rotors on the top and no tail rotor. The two rotors turn in opposite directions to counter each other's centrifugal force and keep the machine from spinning like a top.

The blades of the rotors mesh as they move, which means a synchronizing system is needed to prevent them from colliding. Transmissions for both fore and aft rotor systems are linked through a drive shaft to a transmission that is supposed to keep the rotors apart.

Frances S. McGlade was the last civilian chief of Army safety, a function that has been performed by a military officer since Oct. 1, 1983. McGlade, in a court deposition, said he was told that in the 18 months before the Mannheim accident, there had been "22 identical cases" of failure in synchronization between the rotors of the CH47.

Top Army officials deny that allegation. Assistant Secretary Patrick Hillier, surrounded with the Army's top safety specialists during an interview, said, "I don't think these gentlemen are aware of any previous incidents involving the combining transmission."

The Army, in a written answer to The Washington Post's question of what caused the Mannheim accident, said, "The combining transmission's input pinion bearing failed due to inadequate lubrication. The bearing lubricators had become partially blocked by particulate matter identified as carbonaceous material and walnut shells." The walnut shells were used as an abrasive cleaner during maintenance.

That explanation also is what Boeing Vertol listed in court papers as the cause of the accident, thus putting the blame solely on military maintenance.

However, a U.S. District Court jury in Philadelphia has decided that Boeing Vertol was negligent and that the Chinook had been delivered to the Army with a defect which was a cause of the accident.

The jury's decision was upheld by the trial judge and Boeing Vertol's appeal is pending with the U.S. Court of Appeals for the Third Circuit in Philadelphia. If the plaintiffs are sustained on appeal, trials will begin on the question of how much money the victims' families should receive.

Philip Silverman, an attorney with Speiser, Krause and Madole, a firm that specializes in aviation cases, represents the plaintiffs. He said he agrees that the transmission bearing failed because of oil starvation, but he went beyond that in court papers and in the trial to ask what happened next.

When the bearing failed, a connector between the bearing and the synchronization shaft displaced, or moved off center. Then the shaft began to rub against the side of the opening through which it passed. That side acted like a cutting tool. The shaft was cut and, inevitably, the helicopter crashed, Silverman argued.

In arriving at that scenario, Silverman relied on the notes of a Boeing Vertol engineer who had investigated a 1966 Chinook accident in Vietnam and who had suggested that the opening be enlarged to give more clearance for the connector.

According to a brief filed by Silverman, "Boeing never told the Army that displacement . . . would result in synch shaft failure and there was no recommendation to increase the clearance."

Boeing Vertol lawyers and spokesmen declined to discuss the case or the accident. However, Boeing Vertol argued in court papers that if the Army had made other changes to the helicopter that Boeing Vertol did recommend, the accident would not have happened.

Parts of the Army's official investigation reports of the Mannheim accident are in court records. One investigating team recommended the Army make four changes. One recommendation was accepted and three were not, according to answers the Army provided The Washington Post.

One of the rejected recommendations was to increase the clearance of the drive shaft.

The accepted recommendation was to discontinue use of walnut shells as an abrasive cleaner of the bearing housing.

The accidents involving what is known as mast bumping concerned the Army's workhorse helicopter, the ubiquitous Huey, which became famous in Vietnam for everything from ambulance to gunship duty. It is manufactured by Textron Inc.'s Bell Helicopter Division near Fort Worth.

After years of studying the subject, the Army now is modifying 4,194 helicopters -- the UH1 transports and its armed AH1 Cobra variant -- to reduce the possibility of an almost always fatal bumping occurrence. Since 1967, mast bumping has been a factor in at least 61 noncombat Huey and Cobra accidents that have killed 223 people.

The decision to modify comes after an Army blue-ribbon panel reported last April that mast bumping had been perceived as a problem as early as 1972. "While admitting that hindsight is easier than foresight . . . , the manufacturer and the Army should have moved more swiftly . . . , " the panel said.

The panel was convened after a series of articles by Mark Thompson in the Fort Worth Star-Telegram detailed mast-bumping accidents and what had been to that point all study and little action. The reports earned the Pulitzer Prize on April 24.

The Huey and other Bell models have what is known technically as a "teeter-rotor" system, a two-bladed main rotor. An inevitability of the teeter-rotor design is that if one blade goes up, the other goes down, just like a teeter-totter.

The two rotors are attached to the mast of the helicopter through a doughnut-like hub. If the angle of the blades in relationship to the mast of the helicopter becomes too exaggerated, the underside of the hub will bump or rub the mast, the mast will break and the helicopter will crash.

The Army, Bell and specialists from the Federal Aviation Administration and the National Transportation Safety Board said in interviews that mast bumping is almost never the primary cause of an accident, but occurs after something else goes wrong.

Civil versions of Bell teeter-rotor helicopters have not exhibited mast bumping, FAA and safety board experts said, presumably because civil pilots do not ask the machines to do the same things military pilots do.

Maj. Gen. Richard D. Kenyon, assistant deputy chief of staff for research, development and acquisition for the Army, said in an interview, "I guess I can remember the analysis done on 60 mast-bumping accidents where 69 percent of them were attributed either to a tail rotor failure, an engine failure, a maintenance error or something in which, we feel, but we can't document because there are normally no survivors in these accidents, that the pilot, like I have done at times probably, reacted abruptly and put the control, put the aircraft outside of the prescribed flight envelope."

In other words, the aircraft was asked to do something it could not survive -- the pilot erred.

However, until the blue-ribbon panel met more than 20 years after mast bumping was first suspected as a problem, the Army did nothing to change the helicopter to make the occurrence less likely or less likely to be fatal if it did happen.

In 1981, the Army considered developing a spring that would push the rotor hub away if it got too close to the mast. An internal recommendation was made to go forward with the hub spring.

However, Kenyon said, when that recommendation was submitted it was "not coded" as a high-priority safety item, but as an equipment upgrade which required it to compete with other items in the budget. Further, there had been two consecutive years without a reported mast-bumping incident. The recommendation died.

"If I put myself in their shoes and I saw the trend, with two zero fatality years, I could have made that judgment, I guess," Kenyon said.

Now thicker masts have been installed on the entire Huey fleet and the hub spring has been developed by Bell and the Army to be installed on the Hueys by Army units in the field. The modifications will cost $45 million, for which Bell Helicopter is the contractor.

Those changes will not prevent mast bumping, but, Hillier said, "will increase the margin of safety. We're not even sure how much it increases the margin of safety. Will a little mast bump be all right? We still don't know."

The Huey's teeter-rotor technology, Hillier noted, was developed in the 1950s and "is 30-year-old technology. We don't like the technology." However, the Hueys alone are projected to be in the Army inventory until the year 2010.

On April 19, the Army grounded indefinitely all 630 of its UH60 Black Hawk helicopters, the replacement for the Hueys. The Black Hawk, manufactured by Sikorsky Aircraft, a division of United Technologies Corp., had performed remarkably well during the 1983 invasion of Grenada, remaining aloft despite taking many rounds of fire.

The reason for the grounding is two UH60 crashes -- March 13 and April 18 -- that killed 15 people. "There is no identifiable cause in either" crash, said Lt. Col Miguel E. Monteverde Sr., an Army spokesman.

"We have formed a special working group to go over both the aircraft, our training program, associated equipment and maintenance procedures from stem to sterm," Monteverde said. "The aircraft is too valuable to us and our troop lives are too valuable to us . . . . We're not going to do another mast bumping."