Incident Overview
On March 18, 2011, at approximately 0009 eastern daylight time, an Embraer EMB-145XR, registration N11187, veered off the left side of runway 23 while landing at Akron-Canton Regional Airport, Akron, Ohio. The aircraft was operating as United Express flight 5916 under 14 Code of Federal Regulations Part 121 as a scheduled domestic passenger flight. Visual meteorological conditions prevailed, and the flight operated on an instrument flight rules flight plan. It originated from Chicago O'Hare International Airport (ORD) at 2222.
The three crewmembers and 43 passengers reported no injuries. The airplane sustained minor damage.
Flight Crew Reports
The flight crew reported to an FAA inspector that the flight was uneventful until nose landing gear touchdown. At that point, the airplane made an uncommanded left turn that the pilots could not correct. The airplane veered off the runway pavement before stopping. Passengers deplaned through the main boarding door.
During a telephone interview, the captain stated they performed a visual approach backed up by the instrument landing system, with the glideslope captured at the outer marker. The approach was normal with no system warnings before touchdown. After nose gear touchdown, the airplane veered left; he estimated approximately 3 seconds elapsed from nosewheel touchdown to exiting the runway onto the grass. The first officer attempted to manually disengage nosewheel steering using the switch on his control wheel, but the airplane continued to veer.
The captain noted that the approach plate book slid off its bracket and onto his lap during the event. He tossed it away, and it came to rest on his flight bag behind and to the left of his seat. He stated it may have been near the nosewheel tiller control but was not on the tiller, and was clear before the airplane exited the runway.
The first officer reported that after touchdown, the captain lowered the nosewheel slowly, and the airplane immediately started turning left. He applied hard right rudder, right brake, and activated the nosewheel steering disconnect. He did not recall hearing the usual chime indicating disconnect and did not feel the steering disengage as expected.
Nosewheel Steering System Description
The nosewheel steering system is electro-hydraulic, using inputs from rudder pedals or the captain's tiller. Maximum steering angles are 71 degrees with tiller, 5 degrees with rudder pedals, or 76 degrees with both. A proximity sensor disengages the system if the nose wheel is rotated beyond 7 +/- 1 degrees without tiller engagement. The system can be manually disengaged via switches on control wheels, provided the tiller is not engaged. Disengagement results in a caution alert, master caution light, and "STEER INOP" EICAS message, and allows free castering.
Examination and Testing
On-scene examination revealed skid marks on the runway and a witness mark from the right nose wheel tire chine consistent with left nosewheel steering deflection. On-airplane testing of the nosewheel steering system per manufacturer procedures found no faults. Several components were removed for testing; some parameters were outside specifications, but anomalies would not have caused the described behavior. No anomalies were found that would have precluded normal operation.
Recorded flight data recorder information showed: at 0008, aircraft descended through 1,700 ft on heading 233 degrees. At 0008:45, air/ground switch moved to "Grnd," followed by symmetric spoiler and thrust reverser deployment. Pilot brake pedal activity began then; at 0008:49, copilot right brake pedal activity started. At 0008:52, heading began turning left as airspeed fell below 100 knots. At 0008:53, rudder reached maximum right deflection of 12.7 degrees. At 0008:55, left and right ailerons peaked at 16.5 degrees trailing edge down and 24.4 degrees trailing edge up, respectively. The aircraft came to rest at 0009:04 on heading 199 degrees. Tiller engagement and nosewheel deflection were not recorded parameters.