NTSB Issues Plane Grounding Advisory : Aviation: The recommendation covers the type of commuter craft that crashed in Indiana. It could not take off when icing exists or is forecast.

The National Transportation Safety Board on Monday issued an emergency recommendation that the type of commuter plane that crashed in Indiana a week ago be grounded whenever icing conditions exist or are forecast.

The request for a Federal Aviation Administration directive ordering the grounding is advisory only, “but we feel it needs immediate attention,” said Ted Lopatkiewicz, a spokesman for the NTSB. “They have 90 days to respond, but with recommendations like this, they usually respond much sooner.”

FAA officials were not immediately available for comment.

American Eagle Flight 4184--a European-built, twin-turboprop ATR72--suddenly rolled over and plunged nose-first into a bean field near Roselawn, Ind., after circling on autopilot for more than 30 minutes in subfreezing temperatures and steady rain while awaiting clearance to land at Chicago’s O’Hare International Airport. The crash killed all 68 on board.

Although the NTSB has yet to determine the cause of the crash, attention focused from the outset on the possibility that ice had built up, overburdening the aircraft, reducing the lift provided by the wings and crippling the ailerons--hinged plates on the wings’ trailing edges that move up and down to bank and turn the airliner.

In the recommendations issued Monday, the NTSB noted similarities between the American Eagle crash and an incident in Wisconsin in December, 1988, involving an ATR42, a smaller version of the ATR72.

The ATR42 over Wisconsin was flying on autopilot in icing conditions when it, too, began to roll over, but the pilot was able to recover and the plane landed without incident. Icing has been blamed in the 1987 crash of an ATR42 in the Italian Alps.

“The safety board is concerned that an amount of ice that can be accumulated under some flight conditions during winter operations may be more critical to the flying quality of the ATR42 and ATR72 airplanes than to other airplanes,” the board said Monday.

The ATR planes are mainstays of commuter aviation, and grounding all of them during inclement weather would have a disruptive effect on the industry.

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More than 250 ATR42s and about 130 ATR72s are currently being flown throughout the world--most of them in the United States. American Eagle--a subsidiary of the AMR Co., which also operates American Airlines--currently flies 25 ATR72s.

“Obviously, if the FAA issues an order, we will comply with it,” said Al Becker, a spokesman for American Eagle. “We will cooperate fully.”

Last Thursday, three days after the crash in Indiana, American Eagle’s parent firm--the AMR Co.--issued a bulletin prohibiting use of the autopilots on ATR72s and ATR42s whenever icing conditions exist.

In addition, the firm ordered that the flaps on both planes be fully retracted whenever circling in a holding pattern.

Flaps are flat metal slabs that can be extended back from the wings to increase their lift. Flight 4184 was circling over Roselawn at about 210 m.p.h. with its flaps extended at a 15-degree angle when an alarm sounded, warning the pilot that flap damage could occur at that high a speed.

Sources believe that when the pilot retracted the flaps in response to the alarm, Flight 4184’s problems intensified.

The sources believe the wings already were losing lift because of accumulating ice, and retracting the flaps reduced that lift even more, leaving the plane perilously close to a stall.

“The circumstances of this accident . . . indicate that the use of the autopilot can mask the onset of lateral instability,” the NTSB said Monday.

The agency said that ice apparently built up on the ailerons, crippling them so that they could no longer keep the wings level despite repeated commands from the autopilot.

Reaching its preset limits, the autopilot apparently disengaged, the NTSB said, leaving the pilots with a plane that started to roll out of control before stalling and plunging nose-first toward the ground.