NTSB issue the final report into an accident involving American Eagle flight 4125, an Embraer ERJ-145, N619AE, that occurred on November 11, 2019, at Chicago-O’Hare International Airport (ORD/KORD), Chicago, Illinois:
On November 11, 2019, at about 0742 CST, American Eagle flight 4125, operated by Envoy Air, an EMB145LR, N169AE, experienced a right main landing gear collapse after the aircraft departed runway 10L while landing at Chicago O’Hare International Airport (KORD), Chicago, Illinois. There were no injuries to the 41 passengers and crew onboard and the airplane received substantial damage. There was blowing snow at the time of the accident. The flight was operating under14 CFR part 121 as a domestic passenger flight from Piedmont Triad International Airport (KGSO), Greensboro, North Carolina.
While the airplane was on short final approach to runway 10L, the tower controller issued instructions to the accident flight crew to go-around. (The controller did not provide a reason for the go-around instruction.) The flight crew performed a go-around maneuver and subsequently discussed, with the company dispatcher, the possibility of diverting to the alternate airport or changing the alternate airport to one closer to the airplane’s position. However, the flight crew elected to make another approach to the destination airport.
During the second approach to runway 10L, the tower controller informed the flight crew that the runway condition code was 5/5/5, which indicated “good” braking action across all three runway zones (touchdown/midpoint/rollout). However, the controller also informed the crew that other flight crews had reported the braking action as “medium to poor” until taxiway N3 (which was located about halfway down the runway) and then “poor” past that point. The controller cleared the airplane to land and reported that the wind was from 360° at 17 knots with gusts to 24 knots. Given the runway orientation, the steady-state wind speed would have resulted in a crosswind component of about 16 knots. The company’s maximum crosswind limit during landing was 30 knots for a dry runway or if the braking action is reported as “good”.
The airplane touched down on the runway centerline, but, as the captain applied the brakes and reverse thrust, the airplane moved off the centerline. The crew stated the airplane started swerving to the right when its indicated airspeed was about 80 knots. As the captain applied corrections to maneuver back to the centerline, the airplane started to slide to the left. The captain stated that he applied maximum reverse power and brakes but that the airplane continued to slide to the left.
Flight data recorder (FDR) data indicated that after landing, thrust reverser deployment and brake application, the airplane was tracking slightly right when the captain was commanding slightly left. At 80 knots, the airplane veered to the left and the captain commanded airplane nose right rudder. However, rudder effectiveness at slower airspeeds and with thrust reversers is reduced and the left turn was not arrested. Data also shows that no more than +/- 3 degrees of rudder deflection was used.
The first officer stated that the airplane “experienced an uncommanded swerve” to the left near taxiway N1, which was about one-third of the way down the runway from the approach end. The airplane subsequently slid off the runway at an airspeed of about 60 knots and onto the grass on the left side of the runway. Postaccident examination of the airplane systems revealed no anomalies that would have precluded normal operation.
Light wet snow had started falling at the airport about 3.5 hours before the time of the accident, and about 1.6 inches of snow accumulation was reported at 0600. Clearing operations had been performed on runway 10L, and it was reopened about 1.5 hours before the accident with a runway condition code of 5/5/5 and conditions assessed as 90% wet and 10% with 1/8 inch of wet snow across all three runway zones. A field condition notice to air mission reflecting those conditions was issued at 0624. Given that light wet snow was falling at the time, a reassessment of the runway conditions needed to occur within 90 minutes of the previous assessment, and a 90-minute pavement inspection timer was set in the air traffic control tower.
As snow clearing operations on runway 10L were concluding, airport operations personnel began conducted clearing operations on the two other parallel runways (10C and 10R) on the south side of the airport. Runway 10C remained closed until about 3 minutes before the accident, and runway 10R had not been reopened at the time of the accident because conditions on that runway had not yet improved. Thus, at the time that the accident flight was cleared to land, runway 10L was the only runway on the south side of the airport being used for landing operations.
As previously stated, the tower controller informed the flight crew that the reported braking action for runway 10L was “medium to poor” until taxiway N3 and “poor” past that point. According to Envoy Air’s EMB-140/145 Aircraft Operations Manual, which contained Federal Aviation Administration guidance about runway condition assessments, a pilot report of medium indicated that braking deceleration or directional control was “noticeably reduced,” and a pilot report of poor indicated that braking deceleration or directional control was “significantly reduced.” Both the captain and the first officer indicated that, according to company guidance, the Runway condition codes are “controlling” and that pilot reports are advisory. Thus, it was reasonable for the flight crew to attempt to land on the runway based on the reported Runway condition code of 5/5/5.
The captain’s use of maximum reverse thrust and braking appeared to be consistent with his training. Specifically, the captain stated that he was trained to land on a contaminated runway by applying the brakes evenly and using maximum reverse until the airplane decelerated to about 80 knots. Envoy Air’s guidance stated that reverse thrust was the best aid in stopping on slippery runways and that high levels of symmetrical reverse thrust early in the landing roll would provide the most stopping force.
The captain also stated that he was trained that rudder effectiveness was reduced when using reverse thrust. In this case, the reduced rudder effectiveness was appropriate because the flight crew’s use of reverse thrust helped slow the airplane. Additionally, Envoy Air’s guidance stated that, at lower speeds, nosewheel steering and differential braking would be primarily used for directional control. In this case, the use of the differential braking and nosewheel steering might have helped the airplane track along the runway centerline, but the airplane’s stopping time (and distance) would likely have increased.
After runway 10L reopened at 0618, the controller requested braking action reports from landing airplanes. The flight crew of the first airplane to land on the runway reported braking action as poor. Multiple flight crews of airplanes that landed afterward reported that braking action was medium until taxiway N3 and poor after that point. One flight crew reported that it became “really hard to hold the centerline” after taxiway N3 because of the crosswind. Further, as the controller was issuing instructions to a flight crew for exiting the runway, she described the conditions at taxiway N3 as “slick.” Thus, the conditions on runway 10L had deteriorated and were no longer consistent with the previously published field condition NOTAM indicating that the Runway condition code was 5/5/5.
The airport’s Snow and Ice Control Plan stated that two consecutive reports of poor braking action would trigger either a runway closure or a runway assessment. Although two consecutive reports of poor braking action were not received for the touchdown zone of the runway, multiple reports of poor braking action reports were received for the midpoint zone, which were not consistent with the airport’s previous assessment of the runway.
The southside snow coordinator had been monitoring the status of runway 10L from the air traffic control tower and was aware of the reports of medium and poor braking action. About 0730 (and with about 60 minutes of the 90-minute pavement inspection timer elapsed), he dispatched two airport operations supervisors in two vehicles to conduct friction and condition assessments of runway 10L. One of the supervisors requested clearance onto the runway, but the controller instructed both vehicles to hold short of the runway at their position (taxiway Z). About 2 minutes later, the other supervisor notified the controller that both vehicles were holding short of runway 10L, and the controller acknowledged this information and repeated the hold-short instruction. The accident occurred about 7 minutes 17 seconds after the first airport operations supervisor initially requested access to the runway.
Although airport operations supervisors were standing by to conduct an assessment of runway 10L before the 90-minute pavement inspection timer had elapsed, the available evidence for this accident precluded a determination of why the vehicles were not cleared onto the runway before the accident landing.
– Probable Cause: “The flight crew’s inability to maintain the airplane on the runway centerline after touchdown due to the reduced braking action resulting from the deteriorating weather conditions, which caused the airplane’s departure from the runway surface. Contributing to the accident were the delay in performing the runway assessment for undetermined reasons and failure to close the runway. Also contributing to the accident was the controller’s failure to advise the accident flight crew that braking action was no longer consistent with the previously published notice to air mission, which described braking action as good across all three runway zones.”