CEN11IA234

The flight crew reported that the flight was uneventful until the nosewheel touched down, at which time, the airplane made an uncommanded left turn and then veered off the runway. Examination of the runway revealed a witness mark from the right nosewheel tire chine consistent with a left deflection of the nosewheel steering. Testing of the nosewheel steering system and its components did not reveal any anomalies that would have precluded normal operation. The pilot reported that he used a bracket to support his approach plate book and that, during the event, the book slid off of the bracket and onto his lap. He then tossed the book out of the way. He stated that, at some point, the book may have been in the area of the nosewheel tiller but that it was not on the tiller and that it was clear of the tiller before the airplane exited the runway. Although it is possible that the weight of a book engaged the tiller, it could not be determined if the tiller was engaged during the event.

On March 18, 2011, about 0009 eastern daylight time, an Embraer EMB-145XR, N11187, veered off of the left side of runway 23 while landing at the Akron-Canton Regional Airport, Akron, Ohio. The 3 crewmembers and 43 passengers on board reported no injuries. The airplane sustained minor damage. The airplane was operated by ExpressJet Airlines as United Express flight 5916 as a 14 Code of Federal Regulations Part 121 scheduled domestic passenger flight. Visual meteorological conditions prevailed for the flight which operated on an instrument flight rules flight plan. The flight originated from the Chicago O'Hare International Airport (ORD), Chicago, Illinois, at 2222.The flight crew reported to a Federal Aviation Administration inspector that the flight was uneventful until the nose landing gear touched down on the runway during landing. At that point, the airplane made an uncommanded left turn that the pilots were unable to correct. The airplane veered off the runway pavement before coming to a stop. The passengers were deplaned through the main boarding door of the airplane. During a telephone interview of the flight crew, the captain reported that they made a visual approach that was backed up using the instrument landing system and that the glideslope was captured at the outer marker of the published approach. He reported that the approach was normal and that there were no warnings or messages from the airplane's systems prior to touchdown. During the landing, once the nose landing gear touched down, the airplane veered to the left and he estimated that it was about 3 seconds from the time the nosewheel touched down to the time that the airplane exited the runway onto the grass. He said that during the event, the first officer attempted to manually disengage nosewheel steering using the switch provided on his control wheel, but this action did not prevent the airplane from veering to the side. The captain stated that the approach plate book used during the approach slid off of the side of the bracket and onto his lap during the event. He said that he took the book and tossed it out of the way and that it came to rest on the flight bag behind and to the left of his seat. He said that at some point it may have been in the area of the nosewheel tiller control but was not on the tiller, and that it was clear of the tiller before the airplane exited the runway. The first officer reported that after touchdown, the captain lowered the nosewheel slowly and the airplane started to go to the left immediately. He immediately got on the controls with the captain and applied hard right rudder, right brake, and activated the nosewheel steering disconnect. He stated that when engaging the nosewheel steering disconnect, a chime is usually heard, but he did not remember hearing it during the event. He stated that he did not feel the nosewheel steering disengage, as expected, when the switch was activated. The nosewheel steering system of the airplane was anelectro-hydraulic system that used inputs from either the rudder pedals, or the captain's tiller. The nose wheel steering can be commanded to a maximum angle of 71 degrees when using the tiller, 5 degrees when using the rudder pedals, or 76 degrees using both tiller and rudder pedals. A proximity sensor connected to the feedback unit sensor disengages the system if the nose wheel is rotated beyond 7 +/- 1 degrees when the tiller is not engaged. If the nosewheel steering system disengages in this manner, the system can be reengaged by engaging the tiller when speed is below 25 knots. The steering system may also be manually disengaged through switches located on either control wheel, provided the tiller is not engaged. If the nosewheel steering system is disengaged for any reason while the aircraft is on the ground a caution oral alert will sound, the master caution light will illuminate, and the message "STEER INOP" will display on the EICAS. The system allows for the nose wheel to free caster any time the nose landing gear is on the ground and the nosewheel steering system is disengaged. Manual disengagement of the nosewheel steering system using the flight crew switches would place the nosewheel into this free castering mode. An on-scene examination revealed skid marks on the runway leading to the resting position of the airplane. There was a distinct witness mark that was made by the right nose wheel tire chine on the runway that was consistent with a deflection of the nosewheel steering to the left. Examination of the airplane was conducted which included on-airplane testing of the nosewheel steering system in accordance with the airplane manufacturer's maintenance manual. No faults were found during the ground testing. Several components of the nosewheel steering and braking system were removed from the airplane for testing at the respective manufacturer facilities. Although testing of the individual components did reveal some parameters that were not within manufacturer specifications, the anomalies would not have resulted in the behavior described by the flight crew. No anomalies were found that would have precluded normal operation. Recorded data from the airplane's flight data recorder showed that at 0008, the aircraft descended through 1,700 ft pressure altitude, while on a magnetic heading of approximately 233 degrees. The Air/Ground Switch moved to 'Grnd' at 0008:45, and was followed by symmetric spoiler and thrust reverser deployment. The data showed activity on the pilot brake pedals began at this time. Four seconds later, at 0008:49, the copilot's right brake pedal began to show activity. At 0008:52, the recorded magnetic heading began to swing to the left as the indicated airspeed fell below 100 knots. At 0008:53, the rudder reached its maximum right deflection of 12.7 degrees. At 0008:55, the left and right ailerons reached their maximum deflection of 16.5 degrees TED (trailing edge down) and 24.4 degrees TEU (trailing edge up)respectively. The aircraft came to rest at approximately 0009:04 on a magnetic heading of 199 degrees. Tiller engagement and nosewheel deflection were not recorded parameters.