The Federal Aviation Administration on Friday banned two models of propeller-driven commuter planes from flying in conditions where ice is likely to build up on their wings, the first time the agency has issued such an order.
The FAA made the decision after conducting wind tunnel tests in recent weeks on the ATR-72 aircraft, the type of plane that crashed in Roselawn, Ind., in late October, killing all 68 people on board. The plane was operated by American Eagle, a commuter division of American Airlines.The order affects both the ATR-72 and the ATR-42, a similar but smaller aircraft made by Avions De Transport Regional, a French-Italian consortium formed in 1981. Altogether, there are 153 ATR planes in use in the United States, operated by commuter divisions of Delta, Continental and Trans World Airlines, as well as American.
Airlines that operate the aircraft said they would move the planes to warmer parts of the country where icing was less likely to occur, a shift that is likely to disrupt air travel for thousands of passengers in coming days.
Although these aircraft represent only about 7 percent of this country's commuter airline fleet, they are among the largest commercial propeller-driven aircraft in use.
The agency's decision came more than a month after the National Transportation Safety Board made the same recommendation - that the planes be grounded in icing conditions - to the FAA, which follows such advice by the board in 82 percent of the cases.
The board said it made the recommendation because it feared the design of the plane could result in other crashes under similar conditions.
Although the FAA took pains Friday to point out that it had changed many procedures governing the ATR since the crash, the timing of its decision drew criticism from the International Airline Passengers Association, a Washington organization that monitors air safety around the world.
"Their policy is to expose passengers, pilots and flight attendants to risk while they are trying to figure out the specific problem," said David S. Stempler, executive director of the association. "Our approach and the safety board's approach is to not expose people to these risks until you figure it out. They told us the plane was safe. All of a sudden it's not."
Tom McSweeny, director of the FAA's aircraft certification service, defended the agency's decisions since the crash. "We estab-lished a level of safety that is appropriate for whatever the condition is," he said. "The FAA always errs on the side of being cautious," he said.
Since the crash, the FAA has issued several orders that, among other things, prohibited the use of the autopilot in icing conditions and directed air traffic controllers to give landing priority to such planes in bad weather.
The agency also assembled a team of aviation experts to conduct new tests on the aircraft. Those tests included 300 different wind tunnel tests, in which various shapes were placed on the wings of a scale model of the plane.
"It was apparent," McSweeny said, "that some ice shapes could occur that caused the airplane to behave similarly to what we believe may have happened in the accident."
The ATR-72 that crashed in Indiana tipped 77 degrees to the right, recovered to 59 degrees, then flipped upside down and plunged at 45-degree angle, investigators said last month. They have not concluded what caused that crash, although icing is suspected.
The agency directive specifically prohibits the aircraft from flying when icing conditions are forecast or present. Those conditions exist when the air through which the ATRs would be flying is 40 degrees Fahrenheit or cooler and when there is moisture or precipitation in the air.
The last aircraft to be grounded by the FAA was the DC-10, which was barred from flying for 38 days in 1979 after an American Airlines crash in Chicago killed 273 people.
ATR, which has delivered 404 aircraft worldwide since 1985, said Friday that it regretted the decision. It said that the wind tunnel tests "provide no basis for the action taken by the FAA today." The FAA conducted the tests in Toulouse, France, with the French airline regulatory agency and ATR.