NTSB: Challenger Mistrim Is ‘Unsafe Characteristic’

By Matt Thurber

AINalerts >> July 2008
Safety, Aircraft

The NTSB issued a safety recommendation letter on Thursday warning that pilots may decide to abort takeoffs in Bombardier Challengers if the pilots mistakenly set the pitch trim too far forward, even though the aircraft will lift off at a speed above V2. When it investigated the Feb. 2, 2005, Challenger 600 aborted takeoff accident at Teterboro (N.J.) Airport, the NTSB found that “in the mistrim scenario, with the [center of gravity] at the most forward limit and with the horizontal stabilizer at the nose-down limit of the takeoff green band, the airplane did not rotate, even with full nose-up elevator control, until it was significantly above the nominal rotation speed (V2).” The Board is concerned that pilots in this type of mistrim scenario will abort takeoff at a high speed because they believe the airplane won’t fly. “A delay of this length in the most adverse trim condition is an excessive delay that constitutes an ‘unsafe flight characteristic,’” the NTSB claimed, although certification regulations do not “state explicitly that an excessive delay in rotation during the mistrim is an ‘unsafe flight characteristic’ to be evaluated during certification testing.” The NTSB recommends that the FAA revise certification advisory material to address mistrim-takeoff rotation delays and that Challenger operators “provide training to their pilots that emphasizes the importance of the proper takeoff stabilizer trim setting and that informs pilots about the mistrim-takeoff characteristics of the airplane, including demonstration of these characteristics in a flight simulator.”

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