NTSB Issues Recommendations To Address Challenger Mistrim Takeoffs

Full-Forward CG, Nose-Down Trim Led To 2005 TEB Crash

Stating a potentially dangerous situation could arise for pilots of Bombardier Challenger jets when trying to take off under certain weight and pitch trim conditions, this week the National Transportation Safety Board issued two recommendations to the FAA Federal Aviation Administration to step up training methods and operating guidelines for the aircraft.

The Board cites the February 2, 2005 takeoff crash of a Challenger at New Jersey's Teterboro Airport in making its recommendations. As ANN reported, the National Transportation Safety Board determined that the probable cause was the flight crew's attempt to take off with the center of gravity (c.g.) well forward of the forward takeoff limit, which prevented the airplane from rotating at the expected rotation speed.

"During the Safety Board’s investigation, vehicle performance engineers conducted simulator tests to study takeoff rotation characteristics of the CL-600, as configured at the time of the Teterboro accident, as well as for a normal takeoff and a mist rim-takeoff," writes the NTSB in its latest recommendation. "They found that in the mist rim scenario, with the c.g. 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 (VR, that is, the speed at which the pilot applies elevator control to rotate the airplane for takeoff)."

The Safety Board is concerned that the delayed rotation characteristics of this condition may cause pilots to believe that their airplanes will not fly, leading them to abort takeoff at a speed well above the takeoff-decision speed (V1), with possible catastrophic results," the Board concludes.

The recommendations -- available in full at the FMI link below -- include new language addressing an earlier European Joint Aviation Authorities Notice of Proposed Amendment to be placed in an advisory circular on the mist rim issue, as well as providing Challenger flight crews with addition training emphasizing proper stabilizer trim settings and the possible results of mist rim situations.

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Fonte: Flight Safety Information 23/07/2008.