Test pilots "flying" a simulator programmed to duplicate the damage to the DC10 that crashed in Chicago May 25 have tentatively decided there was no way the American Airlines pilot could have saved his lane, given its condition and the information available to him.
They also have determined that a pilot might have been able to save the plane if he had had precise knowledge of the damage and had taken actions that run contrary to standard pilot training.
About 15 pilots with various backgrounds flew the simulator Friday and today as part of a continuing test program. "We've crashed an awful lot of simulators out there," a senior federal official said. "But if you anticipate it properly, you can fly out of the problem."
Capt. Walter Lux. pilot of american Arlines flight 191, could not have anticipated the problem, because a key warning device was knocked out. That device -- called a stall warning -- is electrically powered. There was no backup power to operate it if the electricity failed. And the electricity failed when the engine and support pylon tore away from the left wing just as flight 191 was leaving the ground.
Such a backup power supply is an "operator's option" on the particular system, Testimony in Congress has shown. That means American Airlines could have chosen to have it but did not.
"Many other airlines have made the same decision; it's always been a lowpriority item before," a federal investigator said. Some airlines have purchased the backup option, accoding to McDonnell Douglas, Manufacturer of the DC10 jumbo jet, but it would not say which ones.
As an airplane gains speed for takeoff, enough air begins to flow over and under the wings to lift it from the ground. If the plane's speed then decreases too much -- if, for instance, it tries to climb too steeply, the air-flow is no longer sufficient to keep it airborne, and it drops. This is stall.
Stall is normally dealt with by putting the aircraft's nose down and picking up speed until adequate lift is restored.
Flight 191's stall warning, had it been working, would probably have sounded a distinctive noise in the cockpit besides shaking the pilot's control stick before airspeed fell to the critical point, investigators said.
In the Chicago probe, the stall warning question is closely tied to the operation of the slats on the wings of the DC10. Slats are huge metal plates that are extended from the leading edge of the wing to give extra lift at low speed.
The slats on the left wing of the crashed plane retracted shortly after takeoff because the hydraulic systems that control them were damaged when the engine came off. Those on the right wing, however, remained extended. That condition, called "asymetrical salts," gave the right wing substantially more lift than the left wing.
In short, there was a left wing stall. That is why the plane rolled sharply to the left before it crashed. The pilot did not have engough altitude to pick up speed and thus restore lift to the left wing.
What could the pilot have done differently?
First, he would have had to know that hw was approaching stall speed and moved to correct it before the stall actually occurred. Once the plane went into the roll, there was nothing he could do.
If he had knowned of the impending stall, according to experts, including one who has flown the simulator at the McDonnell Douglas labs here, the pilot could have lowered the nose of the DC10, thus decresing his angle of climb and increasing the speed of the air flow over the wings.
"His instrument were telling him he had extra airspeed [a condition that was true only for the right wing], so he was trading it for altitude. That is exactly what he was trained to do and what his flight controls told him to do," a pilot said.
The Federal Aviation Administration, working to develop a program that would return the grounded DC10s to service, must address the questions of cockpit warnings, pilot training and unexpected slat retraction, a senior federal official said.
Furthermore, earlier questions about airline maintenance procedures and the manufacture's design of the engine support pylon must be addressed. The earliest a total program for the DC10 could be announced would be late in the coming week, federal officials estimate.
"We've finished our maintenace and design work; now we're concentrating on control questions," an official said.