Flight History
On November 11, 2019, about 0742 central standard time, American Eagle flight 4125, operated by Envoy Air, an Embraer EMB-145, N169AE, departed the left side of runway 10L while landing at Chicago O'Hare International Airport (ORD), Chicago, Illinois. The right main landing gear collapsed. None of the 41 crewmembers and passengers aboard the airplane were injured, and the airplane sustained substantial damage. The flight was operating under 14 CFR Part 121 as a domestic passenger flight that originated from Piedmont Triad International Airport (GSO), Greensboro, North Carolina.
The captain, who was the pilot flying, stated that he and the first officer reviewed expected weather conditions for ORD while at the gate at GSO. The flight departed about 0522 (0622 local time). En route, the flight crew monitored the weather at ORD; visibility was reported between 3/4 and 1 mile.
The Chicago approach controller initially assigned the flight to runway 9L. While on the downwind leg, the controller changed the landing runway to 10L because runway 9L was closed for snow removal. On short final approach to runway 10L, the tower controller instructed the flight to go-around. According to the cockpit voice recorder (CVR), the flight crew did not know the reason for the go-around. After the go-around, the crew discussed options with the flight dispatcher, including diverting to the alternate airport or changing the alternate. They elected to make another approach to ORD. The approach controller provided vectors for an approach to runway 10L.
At 0739:34, the first officer notified the tower that the flight had arrived at the final approach fix. The tower controller stated that the runway condition code (RCC) was 555 – braking medium to poor up to taxiway November 3 and poor past that point. The first officer acknowledged. At 0740:28, the controller cleared the flight to land and reported wind from 360° at 17 knots with gusts to 24 knots. The flight crew reported that the approach was stable and that the airplane broke out of clouds at about 500 ft above ground level. According to flight data recorder (FDR) data, the autopilot was disengaged at 0741:30, but vertical and lateral guidance remained on the flight director until touchdown.
At 0741:32, the first officer called, "runway in sight," and the captain stated, "roger – landing." At 0741:59, the CVR recorded a sound similar to landing gear touchdown. FDR showed that brake pressure began to increase about 1 second later. At 0742:02, thrust reversers were deployed, and groundspeed was 127 knots. The first officer stated, "stay on that centerline," and the captain replied. At 0742:08 and 0742:12, sounds similar to the airplane slowing down and reverse thrust increasing were recorded. At 0742:15, the airplane began to turn left with thrust reverser levers still deployed.
At 0742:22, sounds similar to the thrust reverser levers being moved to forward idle were recorded. As the reversers stowed, brake pressures increased, and the airplane continued turning left. FDR data showed that, when the reversers stowed, groundspeed was 39 knots. At 0742:29, vertical acceleration was 1.64 G and lateral acceleration was -0.85 G. About 1 second later, the master warning "landing gear" sounded until the end of the recording.
The captain reported that the airplane touched down on the runway centerline and that, as brakes were applied, the airplane moved off the centerline. The first officer reported that the airplane started swerving to the right at about 80 knots indicated airspeed. As the captain applied corrections, the airplane started sliding left. The captain stated he applied maximum reverse thrust and brakes, but the airplane continued sliding left at about 60 knots. The first officer stated that the airplane experienced an uncommanded swerve toward taxiway N1. FDR data shows no more than +/- 3 degrees of rudder deflection was used.
The airplane subsequently slid off the end of the runway and onto the grass on the left side. The right main gear collapsed when the airplane departed the runway surface and entered the grass area. At 0742:32, the controller asked if assistance was needed; the first officer replied in the affirmative. The captain determined that passengers should remain aboard until emergency services arrived. The Chicago Fire Department arrived about 0747. No passengers requested medical assistance, and deplaning occurred via the main cabin door and a rescue ramp. The first officer reported that the runway had snow and the nearby taxiway was "very icy." Shuttle buses arrived at the gate about 1 hour after the accident.
Meteorological Conditions
ORD had an automated surface observing system (ASOS) augmented by certified weather observers. On November 10, precipitation started as light rain at 2036 and changed over to light snow at 2351, with temperatures falling to -6.1°C. Snow ended at 1735 on November 11; a total of 3 inches of snow was reported. At 0551 on November 11, the ASOS reported 2 inches of snow on the ground with light snow continuing through the time of the accident. Low instrument flight rules conditions and visibility under 1 statute mile prevailed. The ASOS 5-minute observation for 0740 resulted in a crosswind of 18 to 28 knots and a 3- to 5-knot tailwind component for landing on runway 10L. The 2-minute average wind at 0743 indicated a crosswind of 15 knots with a 4-knot tailwind; the 5-second maximum wind showed a crosswind of 23 knots with a 6-knot tailwind. Numerous pilot reports of light rime icing conditions and braking action ranging from medium to poor were received.
Wreckage and Examination
Post-accident examination found no anomalies with the nosewheel steering system, spoiler system, or braking system. Tires showed no signs of rubber reversion, flat spotting, or abnormal wear. The rudder system and thrust reversers passed operational tests with no faults. The nosewheel steering manifold assembly was functionally tested; during test setup with hydraulic pressure but no electrical command, the C2 output port pressure increased while C1 remained near 0 psi. This behavior was unexpected by the manufacturer, but when electrical command was supplied (as during the accident), the unit performed as expected. The electrohydraulic servo valve was removed for further testing. Functional testing according to the manufacturer's acceptance test procedure found the unit met as-new limits except for a slight exceedance in flow gain. The manufacturer stated this exceedance could result in a small increase in nosewheel deflection speed but would not cause an uncommanded turn and was common with wear. Teardown revealed a small particle of foreign object debris (FOD) adhered to the armature; the FOD was consistent with an organic material, source unidentified. After FOD removal, plots for pressure gain, flow gain, internal leakage, and noise showed some changes but still passed as-new requirements. Additional disassembly revealed that filter seals were beginning to split circumferentially, but no material loss was found. The nosewheel steering electronic control module, feedback unit potentiometer assembly, rudder pedal potentiometer assembly, and brake control unit passed all functional tests.
Additional Information
Envoy Air's EMB-140/145 Aircraft Operations Manual included runway condition assessment matrix guidance from FAA Advisory Circular 91-79A. The manual stated that a runway is considered contaminated when more than 25% of the required field length is covered by more than 1/8 inch of standing water, slush, or wet snow; or by more than 3/4 inch of dry snow, any compacted snow, or any ice. Maximum crosswind during landing was 30 knots, and maximum landing tailwind was 10 knots. The manual noted that braking on a slippery runway can range from fairly good to virtually nil, and that snow-covered runways are at least twice as slippery as dry runways. It stated that on slippery runways, reverse thrust is the best aid in stopping, and that directional control is primarily through rudder, with nosewheel steering and differential braking providing some directional control at lower speeds. The captain reported being trained that rudder effectiveness is reduced with reverse thrust, and to land on a contaminated runway by applying brakes evenly with constant pressure while maintaining centerline, using maximum reverse until decelerating to about 80 knots then as needed.