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WASHINGTON (Reuters) - U.S. safety investigators have for years pressed regulators to take stronger and swifter action to mitigate the dangerous effects of aircraft icing, a stand prompted by crashes more than 15 years ago.
Icing quickly emerged as a leading possible cause for why a Continental Connection turboprop fell out of the sky in wintry conditions and plunged into a house near Buffalo, New York, late on Thursday, killing all 49 people on the plane and one person on the ground.
While the National Transportation Safety Board investigation of commuter Flight 3047 will take several months at least, records showed the board has been dissatisfied with the Federal Aviation Administration's response to four of its icing-related safety recommendations, one dating to 1996.
The safety board issued a safety alert last December based on one of the two outstanding icing-related recommendations that it made to the FAA in 2007.
That one would require crews to activate anti-icing systems or rubber "boots" designed to break up accumulated ice on the leading edge, or front, of the wings once a plane enters icy conditions, unless there is a specific instruction from the manufacturer not to do so.
Safety board investigators in Buffalo said on Friday that "black box" recordings showed the crew of Flight 3407 commented on ice buildup on the windshield and the leading edge of the wings of the year-old Dash 8 Q400 shortly before the crash.
It was not clear what procedures were in place for the crew at Colgan Air, which was operating the flight. Colgan is a unit of Pinnacle Airlines.
Officials at Pinnacle and aircraft manufacturer Bombardier Inc could not be reached for comment late on Friday. The Dash 8 Q400 has had a good safety record, officials said. Colgan Dash 8s carried 941,000 passengers on 19,000 flights during the first 11 months of 2008, federal records show.
Even a light coating of ice no rougher than sandpaper can cut the amount of lift generated by the wings and increase the minimum speed at which the wing ceases to produce lift, a condition known as stall.
Three major icing-related accidents -- including one in Indiana that killed 68 people in 1994 and another about two years later in Detroit that killed 29 -- focused attention on icing and turboprops.
Turboprops are more vulnerable to icing than jets because they spend more time at lower altitudes where icing is likely to occur.
FAA safety orders, aircraft modifications and changes to pilot training resulted from inquiries into the crashes, but the safety board believes regulators are moving too slowly on its call for stricter action.
Currently, the FAA has three rules in the pipeline to address the NTSB icing recommendations. But there is no timetable for finalizing them and no assurance that the safety board will be satisfied.
Laura Brown, an FAA spokeswoman, said one proposal would allow pilots to more quickly detect icing and address it. "It would help prevent accidents where pilots don't know it's building up," she said.
Additional reporting by Tim Dobbyn; Editing by Xavier Briand