Icing Suspected in Crash of Commuter Plane : Disaster: Turboprop was approaching a town in Minnesota in freezing drizzle when it stalled and slammed into the ground. All 18 aboard were killed.

Ice accumulating on the wings, tail and fuselage may have been a major factor in the crash of a Northwest Airlink commuter plane near Hibbing, Minn., that claimed the lives of all 18 aboard, sources close to the accident investigation said Thursday.

The twin-engine turboprop disappeared from air traffic controllers’ radar screens as the plane was preparing to land at Hibbing in a freezing drizzle, officials said. Seconds later, the plane slammed into a snow-covered mound of mining waste about a mile short of the airport.

The National Transportation Safety Board, which sent a team of experts from Washington to study the crash, said it probably will be months before the cause of the accident is determined officially.

However, sources close to the probe said the weather Wednesday night was conducive to a buildup of ice, and the plane--a British Aerospace Jetstream 31--may be especially susceptible to icing.

NTSB experts say a buildup of ice--even in layers less than one-tenth of an inch thick--can add greatly to the weight a plane is carrying and distort and roughen the surface of the aircraft’s wings, tail and control surfaces.

When the smooth flow of air over wings and other aerodynamic surfaces is interrupted, the result can be a stall--a condition in which the wings and tail no longer provide adequate lift and stability to hold the plane up in the air on an even keel.

In a typical stall, a plane will suddenly plunge nose down toward the ground. If altitude is sufficient and the plane’s controls are working properly, a pilot usually can recover from a stall.

However, in cases where icing fouls the control surfaces of a plane, recovery from a stall can be extremely difficult.

Although the Jetstream 31 was designed to operate in inclement winter weather, concerns have arisen since the December, 1989, crash of one of the planes that was blamed, in part, on icing.

That crash, approximately 400 feet short of a runway at Tri-Cities Airport in Pasco, Wash., killed all six people aboard United Express Flight 2415.

The NTSB concluded that the crash of Flight 2415 was caused by a stall that occurred as the plane was preparing to land.

“Contributing to that stall,” the NTSB said, “was the accumulation of airframe ice that degraded the aerodynamic performance of the airplane.”

Since the crash of Flight 2415, the NTSB has been pressing the Federal Aviation Administration for tests and modifications intended to make the Jetstream 31 safer during icing conditions.

*

According to correspondence between the two agencies, the FAA has agreed with and implemented some of the NTSB’s recommendations, is working on others and has found still others unwarranted.

Icing has been blamed in at least two of this country’s worst air disasters in recent years--the 1982 crash of an Air Florida Boeing 737 into the Potomac River in Washington that killed 78 and the crash of a Continental Airlines DC-9 in Denver in 1987 that killed 28 of the 82 aboard.

Investigators of Wednesday’s crash said the Northwest plane--being operated by Express Airlines II as Flight 5719--was en route from Minneapolis north to Hibbing, a distance of about 200 miles.