DCA23LA005

Following a normal touchdown, spoilers, reverse thrust, and wheel braking was used for the initial deceleration (about 5 knots/second), and the airplane tracked the centerline of the runway for about 9 seconds. About 1-2 seconds before the thrust reversers were stowed, the lateral acceleration began to increase (consistent with a right turning tendency). Subsequently, the magnetic heading began to increase as the airplane began a continuous right turn. The flight crew made two brief 4° to 5° left rudder inputs (each lasting 1 second or less) followed by increased wheel braking that provided more brake pressure on the left main landing gear wheels than on the right main landing gear wheels. The airplane continued to turn right, departed the runway surface into the grass alongside the runway, and came to rest on an adjacent taxiway. The airplane sustained minor impact damage to the left wingtip and a puncture in the left wing leading edge. The investigation was unable to determine what caused the airplane’s continuous right turn. The thrust reverser use was asymmetric with the peak right engine power about 12% higher than the peak left engine power, which would have produced a right-turn tendency. However, the amount of asymmetry was brief, not unusual, and unlikely to cause a continuous right turn. Once the reversers were stowed, any right-turn tendency due to asymmetrical reverse thrust would no longer be present. Three previous landings that involved the incident airplane revealed thrust asymmetries of 5% to 15% (favoring the right engine) during reverser use, and no loss of directional control ensued. For the incident landing, the right turn persisted well after the stowage of the thrust reversers. The flight crew’s two brief left rudder inputs and increased wheel braking on the left main wheels would have provided some left-turn tendency to counter the right turn; however, the right turn continued. The reported weather conditions included a crosswind from the right, which could produce a right-turning tendency. However, the crosswind component was about 3 knots, which would have had a negligible effect on the airplane. The rudder pedals also control the nosewheel steering angle. A full rudder pedal input (25°) will move the nosewheel to a maximum of 5.3° left or right. Using the rudder pedals to sufficiently turn the nosewheel is particularly important as the airplane slows and the rudder becomes less effective for directional control. Had the flight crew made a larger and sustained left rudder pedal input, the rudder surface would have deflected to generate an opposing aerodynamic yawing moment and the nosewheel would have turned to the left (or turned farther so) for a longer period, both of which would likely have been more effective in countering the airplane’s turn to the right. The investigation found no indications of a nosewheel steering system failure or malfunction in the recorded data or the operator’s post-incident examination ofthe airplane. However, because neither the nosewheel steering angle nor tiller control were required/recorded parameters on the flight data recorder, a determination regarding the operation of the nosewheel steering system could not be made. The flight crew’s left differential braking (until the airplane departed the runway) would have provided some left-turning tendency to counter the right turn. Although differential braking is a technique that can be used to help steer the airplane, the operator’s flight crew manual did not reference the use of differential braking for a normal landing. The manual advised that rudder steering (via the pedals) should be used at all speeds. Thus, the flight crew should have used the rudder pedals which would have provided aerodynamic yaw via the rudder surface as well turning the nosewheel steering, to prevent the airplane from departing the runway.

On October 5, 2022, at 1859 eastern daylight time, Air Wisconsin flight 3318, a Bombardier CL-600-2B19, N447AW, sustained minor damage during a runway excursion after landing on runway 24L at James M. Cox Dayton International Airport (DAY), Dayton, Ohio. The 3 crewmembers and 42 passengers aboard the airplane were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 121 scheduled domestic passenger flight from Dulles International Airport (IAD), Dulles, Virginia to DAY. The captain was the pilot flying, and the first officer was the pilot monitoring. Flight data recorder (FDR) data showed that the airplane touched down at an airspeed of about 127 knots. After main gear touchdown, the spoilers deployed, wheel braking (on both the left and right main gear brakes) began to increase, and the airplane tracked along the runway heading for about 9 seconds. The initial deceleration rate was about 5 knots/second. According to the cockpit voice recorder (CVR), a sound consistent with the nosewheel tires rolling over runway grooves began when the nosewheel touched down, which occurred about 1 to 2 seconds after main gear touchdown. The FDR showed that, about 3 seconds after nosewheel touchdown, both thrust reversers were deployed. The left thrust reverser remained deployed for about 6 seconds, and the right thrust reverser remained deployed for about 4 seconds. While the thrust reversers were deployed, the left and right engine thrust increased to a peak of about 57% and about 70% N1 (engine fan speed), respectively. The captain reported that, after deploying the thrust reversers, he navigated the airplane along the runway centerline during the initial rollout. FDR data showed that the lateral acceleration began to increase (consistent with a right turning tendency) 1-2 seconds before the thrust reversers began to stow. The captain stated that, as he started to stow the reversers, the airplane began veering to the right. FDR data showed that as the reversers were stowed, at a groundspeed of about 97 knots, the magnetic heading began to increase. The captain also stated that he used the left rudder pedal to command a left nosewheel steering correction and applied differential braking toward the left but that these actions did not counteract the airplane’s movement to the right. The first officer recalled that he also applied braking “when it was apparent” that the airplane would depart the runway. The airplane departed the runway surface about 12 seconds after nosewheel touchdown, traveled through the grass alongside the runway and came to rest on an adjacent taxiway, as shown in figure 1. Figure 1. Overhead image of the airport with the airplane’s final resting location. After the airplane came to a stop, the captain noticed that the No. 1 (left outboard) brake temperature monitor was at 7 (on a scale of 0 to 20 with 20 being the highest reading). The remaining three brake temperature monitors were “in the green” with nonehigher than 5. The FDR did not record the brake temperature monitor values; however, a “Brake Overheat Warning” message if triggered would have been recorded, which it was not. The higher temperature of the No.1 brake reported by the captain was consistent with the higher braking pressure captured for the left outboard main landing gear wheel by the FDR. The captain further reported that no warning, caution, or abnormal indications appeared on any of the flight deck displays. Tire marks were visible on the runway surface and extended from the runway centerline, curved to the right, and led to the runway edge. Six distinct marks (one for each tire) were observed as shown in figure 2. Figure 2. Tire marks on runway (Source: Air Wisconsin). At 1856, the reported weather at DAY included wind from 350° at 3 knots (a right crosswind), visibility 10 miles, and scattered clouds at 25,000 ft. The operator reported that the runway was dry. A review of the CVR revealed no aural alerts during the landing. A noise consistent with the nosewheel tires rolling over runway grooves began when the nosewheel touched down. This noise continued for about 12 seconds. A review of FDR data revealed no system fault indications. The FDR was not required to record the nosewheel steering angle and the commanded nosewheel steering position, which is based on inputs from the steering tiller control on the pilot’s side console, or from the pilot or co-pilot rudder pedals. The nosewheel steering angle moves with the rudder when the rudder pedals are deflected. The nosewheel can be commanded to a maximum of 5.3° left or right of center via the rudder pedals. The nosewheel can be moved up to 70° left or right of center via the tiller control. According to FDR data, the following events occurred from the time the lateral acceleration began to increase until the airplane came to rest on the adjacent taxiway. · The rudder was deflected 2° to the right for less than 1 second. · Two successive deflections of the rudder to the left occurred: from neutral to 5° and back to neutral and then neutral to 4° and back to neutral. Each deflection lasted up to 1 second. Afterward, the rudder remained within about 1° of neutral until the runway departure. · About the same time as the first rudder deflection, lateral acceleration began to increase (consistent with a right turn). The airplane’s magnetic heading began turning toward the right about 1-2 seconds later. · Before the left rudder deflections, the brake pressure on all four-wheel brakes (two wheels each on the left and the right main landing gear) increased equally through about 500 to 600 pounds per square inch (psi). As the rudder deflections occurred, the overall brake pressure continued to increase with additional brake pressure applied to the left main landing gear wheels. The left gear outboard wheel brake pressure increased to about 1,900 psi, and the right gear inboard wheel increased to about 1,100 psi and then briefly to about1,400 psi. This period of increased and differential braking continued for 4-8 seconds, until the airplane departed the runway. During this period the average of the brake pressures on the left main landing gear wheels exceeded those on the right main landing gear wheels by 440 to 720 psi. Increased wheel loading on the left main landing gear tires due to the right turn, would generally enable higher applied wheel brake pressures on the left main gear wheels than the right main gear wheels. · As the airplane departed the runway, a slight decrease in vertical acceleration occurred, the brake pressures decreased, and the nosewheel tire noise captured by the CVR ceased. The runway departure occurred at a groundspeed of about 57 knots and a heading of 260° (19° right of the 241° runway heading). · The airplane made a continuous right turn from the time that the turn began to the time that the airplane came to rest. The rate of the turn increased slightly as the airplane traveled through the grass, as shown in figure 3. Figure 3. Selected FDR parameters. For a portion of thrust reverser deployment during the airplane’s three previous landings, the right engine thrust was slightly greater (5% to 15% N1) than the left engine thrust. The thrust profiles during reverse were slightly different among all four landings (incident and 3 previous), but the second previous landing was the most similar to the incident landing. According to the airplane manufacturer, the maximum rudder travel is 25° left or right of neutral (center) for the accident airplane’s configuration. A review of preflight control checks captured by the FDR confirmed that the maximum rudder travel was 25° left and right of neutral. According to the Air Wisconsin flight crew manual, rudder steering, using either the pilot or co-pilot rudder pedals, should be used to maintain directional control during landing at all speeds. The manual does not discuss the use of differential braking during a normal landing. However, it is noted in some abnormal procedures (such as in the event of a loss of hydraulic pressure) to “use differential braking, rudder and engine thrust as required to assist in directional control.” Post-incident examination of the airplane, which included the rudder and nosewheel steering systems, was performed by Air Wisconsin. No anomalies were reported. The airplane sustained minor impact damage to the left wingtip and a puncture in the left wing’s leading edge. Airport police reported that a taxiway sign located in the grass near the edge of taxiway G was damaged. NTSB investigation DCA22LA182 involved a CL-600-2B19 that also experienced a runway excursion to the right, for reasons that could not be determined. The incident occurred in Houston, Texas on May 11, 2022. The report for that investigation is available here: DCA22LA182