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Ice on wings suspected in Montana crash

WASHINGTON – Speculation over the crash of a single-engine turboprop plane into a cemetery shifted to ice on the wings Monday after it became less likely that overloading was to blame, given that half of the 14 people on board were small children.

While descending Sunday in preparation for landing at the Bert Mooney Airport in Butte, Mont., the plane passed through a layer of air at about 1,500 feet that was conducive to icing because the temperatures were below freezing and the air “had 100 percent relative humidity or was saturated,” according to AccuWeather.com, a forecasting service in State College, Pa.

Safety experts said similar icing condition existed when a Continental Airlines twin-engine turboprop crashed into a home near Buffalo Niagara International Airport last month, killing 50.

A possible aerodynamic stall in which ice causes the plane to lose lift, and the pilot’s reaction to it, has been the focus of the Buffalo investigation.

“It’s Buffalo all over again, or it could be,” said John Goglia, a former member of the National Transportation Safety Board. “Icing, given those conditions, is certainly going to be high on the list of things to look at for the investigators.”

Mark Rosenker, acting NTSB chairman, told reporters in Montana that investigators would look at icing on the wings as a factor.

“We will be looking at everything as it relates to the weather,” he said.

The plane, designed to carry 10 people, crashed 500 feet short of the Montana airport runway Sunday, nose-diving into a cemetery and killing seven adults and seven children aboard. Relatives said the victims were headed to an exclusive resort on a ski vacation, and gave the children’s ages as 1, 3, 5, 7 and 9, plus two 4-year-olds.

Safety experts said finding the cause of the crash is likely to be significantly complicated by the absence of either a cockpit voice recorder or a flight data recorder, which isn’t required for smaller aircraft that don’t fly commercial passengers like airlines and charter services.

Former NTSB chairman Jim Hall pointed to similarities between the Montana crash and a March 26, 2005, crash near Bellefonte, Pa., in which a pilot and five passengers were killed.

The plane in both cases was the Pilatus PC 12/45 and was on approach to an airport. In both cases there were reports of conditions conducive to icing at lower elevations and witness reports that the plane appeared to dive into the ground.

“I’m certain they are also going to look at the weather conditions at the time and the pilot’s training,” Hall said. He pointed to a recommendation on NTSB’s “most wanted list” of safety improvements that FAA test the ability of turboprop planes to withstand a particular type of icing condition called “super cooled liquid drops” before certifying the aircraft design for flight. FAA officials have said they’re working on that recommendation.

Hours after the crash, federal investigators had focused on overloading as a possible cause.

“It will take us a while to understand,” Rosenker said. “We have to get the weights of all the passengers, we have to get the weight of the fuel, all of the luggage.”

Goglia said the Pilatus has a powerful engine for its size and is unlikely to be affected by the additional weight of a few children.

Standard flight procedures are for the pilot to file a report on the plane’s weight, including the weight of the passengers and the baggage and how that weight would be distributed around the plane, before taking off, safety experts said.

Federal Aviation Administration certification records for the Pilataus PC-12-47, the type of plane that crashed, give the aircraft’s maximum landing weight as 9,921 pounds, including a maximum baggage weight of 400 pounds stored in the baggage compartment at the rear of the cabin. The document doesn’t specify a separate weight for passengers.

Peter Felsch, a meteorologist at the National Weather Service, said conditions measured on the ground not long after the 2:30 p.m. MDT crash were fair – winds of about 9 mph, 10 miles visibility, a temperature of 44 degrees Fahrenheit and a “broken cloud deck at 6,500 feet.”

The Pilatus PC 12/45 is certified for flight into known icing conditions, according to the manufacturers’ Web site and pilots who have flown the plane.

However, like all turboprop planes, it relies on deicing boots – strips of rubber-like material on the leading edge of the wings and the horizontal part of the tail – that inflate and contract to break up ice. That technology, which goes back decades, isn’t as effective at eliminating ice as the heat that jetliners divert from their engines to their wings.

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