Ice on the wings can cause ATR commuter planes like the one that crashed in Indiana in October to roll suddenly, but the pilot can recover by applying firm pressure to the controls, the manufacturer said Thursday.
Pilots who tested the ATR-72 created "a reasonably close duplication" of the initial roll that preceded the crash of American Eagle Flight 4184, and they were able to pull the craft out of it, said Gilbert Defer, flight testing director for Avions de Transport Regional, or ATR.
He testified before a National Transportation Safety Board hearing into the cause of the Oct. 31 crash that killed all 68 people aboard.
But Paul McCarthy of the Air Line Pilots Assn. said pilots have an easier time recovering from a roll in a controlled situation.
"You cannot say that because a test pilot did something in a known condition, you should be able to do it in a live condition," he said.
He said the ATR test proved that ice buildup caused the accident.
Defer and Capt. Robert Briot, ATR vice president of flight operations, said Flight 4184's accident and subsequent testing changed the way they look at earlier accidents.
In March, 1993, an ATR-42 on the way to Newark, N.J., suddenly tilted to the right. The autopilot snapped off and the plane tilted twice more before pilots regained control and landed.
Briot said at the time that the mishap was attributed to turbulence.
"When we look at the Newark incident, we look now with completely different eyes," Briot said.
Investigators have said ice on the wings of Flight 4148 may have disrupted their aerodynamic shape, reducing their lift.
With the plane on automatic pilot in a holding pattern for Chicago's O'Hare International Airport, the crew may not have realized the danger until the craft became uncontrollable, investigators say. The plane flipped over and plummeted to the ground at more than 400 m.p.h.