Shaken and disappointed, Government engineers set out today to pin down what went wrong in the fiery destruction of an unmanned airliner in a test crash.
The consensus was that the concept of a fire-retarding fuel mixture that failed to prevent a fireball in Saturday's crash deserved future study.
Safety specialists emphasized that it would take a long time to reconstruct precisely the sequence of events that left the four-engine Boeing 720 a much more devastated wreck than had been expected.
The fuel mix, which was designed to prevent an explosive burst of flames in case of an accident, was promising in severe tests on the ground, but was unable to live up to a hoped-for performance level in a real air-to-ground crash.
More Violent Crash
The flight path over which the plane was guided by remote control produced a more violent crash than had been planned, and this, the experts said, may have exacerbated the performance problem with the fuel mix.Continue reading the main story
Finally, it was generally acknowledged that the setback had virtually killed a Federal Aviation Administration plan to begin a rule-making process aimed at requiring regular airline use of a fire-retarding fuel mix, perhaps by 1990 or soon thereafter.
The 20-year-old airliner used for the test crash carried 75 dummies in passenger and cabin seats when it took off shortly after 9 A.M. Pacific time from the runway on the desert floor here. It was flown by remote control from a mock cockpit on the ground six miles from the crash site.
About nine minutes later, Fitzhugh Fulton, a veteran pilot for the National Aeronautics and Space Administration, sent signals putting the aircraft into its landing glide. The descent was intentionally several times as steep as in a normal approach to a runway. The wheels were left retracted. Plane Stops Quickly
The plane smashed into the ground a trifle short and with the left wing a little low. As planned, a row of metal devices cut into the bottom of the wings like can openers, releasing the special fuel. The plane was expected to slide straight ahead, trailing the released fuel to the rear. Instead, it swung 90 degrees to the left, and stopped more abruptly than planned. It was quickly enveloped in a towering mass of red flames.
Despite the outcome, Government and industry officials appeared willing to continue efforts to produce a practical way to minimize the fire risk from fuel spilled in accidents.
''I hope this is not the death knell of anti-misting kerosene,'' Cesar Caiafa of the Federal agency said, referring to the special fuel mixture used Saturday. ''I think it's a viable concept. There's some way to stop a fireball from developing.''
Mr. Caiafa is not directly involved in the fuel program but is manager of the aviation agency's program that concentrates on projects to make airliner cabins safer by use of improved aircraft structures, seats, restraint equipment and other interior furnishings. Both projects are the work of the F.A.A.'s Technical Center in Atlantic City. Interior Appears Gutted
Initial examination of the wrecked Boeing 720, a slightly smaller sister of the familiar Boeing 707, showed that the interior had been totally gutted by the fire that the crash produced.
Mr. Caiafa and his team had hoped to recover some of the newly developed passenger seats to compare how they fared with how the conventional seats did that were installed around them. The team also wanted to recover the dummies for similar comparisons.
The new seats were fitted with a layer of material designed to keep flames from spreading between the cushion and the outer decorative cover. Some seats also were fitted with legs built to absorb shock.
It appeared that the fire was so intense that little will be left for a visible examination. However, reams of data on impact forces were electronically relayed to the ground, and are expected to prove of great value to researchers.
Some officials in the fuel-mix program said that the perception of spectacular failure was far off the mark and that the fuel mix had been partly successful. What an Additive Does
When a jet powered by conventional fuel crashes and a tank is ruptured, fuel pouring out is converted by the swiftly moving air stream into a mist of small droplets. This mist can be readily exploded into a fireball by any number of ignition sources.
By mixing conventional fuel with a special additive, a polymer of long- chain molecules, the formation of the fine explosive mist can be retarded. The work has been done by Imperial Chemical Industries of London and its American subsidiary.
In an interview today, Fred Waite, the chemical company's scientist mainly responsible for the development of the special additive, stressed that there had been two eruptions of fire in yesterday's crash.
The first one, he said, had quickly extinguished itself and had not attached itself to the body of the plane, according to preliminary study.
This happened, Mr. Waite said, because the fuel mix had been ejected too quickly for the long-chain molecules in the additive to disentangle. This minimized the formation of an easily explodable mist of small fuel droplets.
The main conflagration, Mr. Waite suggested, developed after the plane had slowed somewhat. Most of the fuel mix, he said, was not subjected to the rapid ejection and contact with a rapidly moving air stream that is necessary to prevents the mist from forming. This portion of the fuel was apparently consumed in the the second eruption of flame.Continue reading the main story