NTSB Factual Report

On December 26, 2006, about 0815 central standard time, a Gates Learjet 35A airplane, N136WE, sustained substantial damage when its right wing collided with terrain during landing at the Nashville International Airport, Nashville, Tennessee. The airplane was being operated by Secure Air Charter, Nashville, as an instrument flight rules (IFR) on-demand passenger flight under Title 14, CFR Part 135, when the accident occurred. The airline transport certificated pilot, first officer, and five passengers, were not injured. Visual meteorological conditions prevailed, and an IFR flight plan was filed. The flight departed the Raleigh-Durham International Airport, Raleigh, North Carolina, about 0853 eastern standard time.

In a written statement provided to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) dated December 12, the first officer wrote that while inbound on the final approach course to the runway, the "AUG/AIL" (aileron augmentation) light illuminated indicating a system malfunction. He reported that the "spoileron" system was reset per the approved flight manual, and the light went out. According to the first officer, the light stayed off, and the approach was continued. He reported that during the landing, while in ground effect, the AUG/AIL lamp illuminated again, and the right wing dropped, striking the ground. He wrote that the captain, who was on the controls, "put in full left deflection trying to compensate, without success." The landing continued without further incident, and the airplane taxied to the ramp.

The airplane landed on runway 2C (center) with a magnetic runway heading of 020 degrees. The official weather observation for the Nashville International Airport at 0753 reported winds 310 degrees, 12 knots, with gusts to 17 knots. The first officer reported the winds at the time of the accident, 310 degrees at 12 knots, with gusts to 19 knots. According to the Lear 35A Flight Manual (FM), Wind Components Chart, an angle of 70 degrees between the prevailing wind direction and the runway heading, would produce respective crosswind components for the observation of 11 knots steady, and 16 knots during gusts. The corresponding components for the winds as reported by the first officer, would be 11 knots steady, with 18 knots during gusts. The FM indicates a maximum demonstrated crosswind component, when the wind is 90 degrees to the runway heading, of 24.7 knots. The FAA approved Master Minimum Equipment List (MMEL) Revision 6, dated November 30, 2006, limits the airplane to 20 knots maximum crosswind component with the AUG/AIL system inoperative. The FM does not address the continued operation and landing of the airplane if the AUG/AIL reset procedure fails.

The augmented aileron (spoileron) system was incorporated into the airplane design to improve handling qualities (roll axis) at lower airspeeds. When the flaps are retracted above 25 degrees the augmentation system is disabled, and only the speed brake function is operational. When the flaps are extended below the 25 degrees position, the augmentation system is active, and as the airplane is banked, the corresponding spoiler board is lifted to aid the lifted aileron. The automatic function of the system and spoiler deflection ratio is computer controlled, and includes limits of deflection based on aileron travel. The system will shutdown automatically if an anomaly is detected, leaving the aileron without augmentation, and a reduced roll rate. An enunciator panel warning light visually indicates a system anomaly.

The airplane received structural damage to the right wing outboard of the aileron, damaging a wing spar. An examination of the aileron augmentation system revealed an anomaly in the computer that controls the AUG/AIL system. The computer was replaced, and the system functioned normally.

NTSB Probable Cause

The pilot's inadequate compensation for gusty crosswind conditions during landing, which resulted in a loss of control and collision with the runway. Factors contributing to the accident were the failure of the aileron augmentation (spoiler) flight control system, diminished directional (roll) control, and crosswind gusts.