In an unusual move last week, the NTSB issued an Alert Letter directly to pilots, advising them to conduct visual and tactile inspections of airplane wing upper surfaces to check for ice and frost. The safety board said that the Nov. 28 accident at Montrose, Colo., involving a Bombardier Challenger 604 that crashed on takeoff, killing three people, has generated much discussion about the effects of wing upper-surface ice accumulations. The safety board said that many pilots do not recognize that minute amounts of ice adhering to a wing can cause severe aerodynamic and control penalties. The board also said that many pilots have misconceptions about coping with icing, such as that they can "power through" any degradation in performance from ice on the wings. But engine power will not prevent a stall and loss of control at liftoff, where the highest angles of attack are normally achieved, the NTSB said. Although the Montrose crash investigation is still underway, the NTSB said its preliminary findings show that atmospheric conditions conducive to upper-wing-surface ice accumulation existed at the time of the accident. The Alert Letter follows a Safety Recommendation that was issued to the FAA on Dec. 15, regarding icing issues relevant to Cessna Caravans.