2011 ExpressJet Airlines runway excursion at Quad City International Airport (N27152)

Incident Overview and Flight Details On August 29, 2011, at approximately 1236 central daylight time, an Embraer EMB 145 XR, registration N27152, operated by ExpressJet Airlines as United Express flight 5821, departed the left side of runway 10 during the landing rollout at Quad City International Airport in Moline, Illinois. The aircraft was on a domestic passenger flight from Denver International Airport under 14 Code of Federal Regulations Part 121. There were 50 passengers and 3 crew members on board, with no injuries reported. The airplane sustained minor damage. ## Meteorological and Operational Conditions Winds were calm, and visual meteorological conditions prevailed at the time of the incident. According to crew statements, the approach, flare, touchdown, and landing were normal until the nose wheel touched down. At that point, the aircraft began to veer left of the centerline. The crew applied right rudder and right differential braking to attempt to maintain the centerline. However, at an airspeed of approximately 90 knots, the aircraft began to turn hard left. It departed the left side of runway 10, briefly regained a heading parallel to the runway, then turned left again, coming to rest at a magnetic heading of approximately 76 degrees. During the excursion, the aircraft struck a taxiway sign and crossed taxiway Echo. Both the Captain and First Officer reported pressing the nose wheel steering disengage switch during the event. ## Aircraft and Airport Information The aircraft was an Embraer EMB 145 XR, registration N27152, serial number 145759. It was built in 2003 and had accrued 22,705 hours and 12,180 cycles at the time of the incident. ## Wreckage and Impact Information The nose tires, left main tires, and right main tires left faint but identifiable witness marks on the runway throughout the initial hard left turn. The aircraft’s final position was in the grass, with the nose wheel approximately 144 feet to the left of the runway edge. Damage included multiple skin tears on the left and underside of the fuselage, numerous dents on the left side of the fuselage, damage to the outboard wheel fairing for the right main gear, identical gouges on the leading edges of the nose wheel doors, a bent nose wheel drag brace pin, and broken nose wheel landing lights. ## Additional Information and Service Bulletin Embraer issued Service Bulletin 145-32-0099 (current revision 03, dated April 8, 2005) to address premature deterioration of O-ring seals within the Electro Hydraulic Servovalve (EHSV). The bulletin noted instances of uncommanded swerving on the ground, with three cases confirmed to involve a failure in the Nose Wheel Steering Hydraulic Manifold EHSV. In all cases, the Nose Wheel Steering system did not respond to cockpit steering commands. The manifold failures were traced to premature deterioration of an O-ring in the EHSV, which converts electrical steering commands into hydraulic pressure. The bulletin required the manifold assembly to be fitted with an EHSV screened to meet HR Textron document DV1719, which specifies critical dimensional requirements, including filter plug outer diameters. An “A” suffix is applied to valve serial numbers that meet these requirements. The incident EHSV serial number was stamped with the “A” suffix. ## Flight Recorder Data The Flight Data Recorder (FDR) was a Honeywell SSFDR, Model 980-4700-042, Serial Number 9753. The recorder was in good condition, and data were extracted normally. The event landing and rollout were captured in the data. ## Tests and Research Following the event, the spoilers, thrust reversers, and rudder functioned with no anomalies identified. The braking system was checked per the Embraer 145 Aircraft Maintenance Manual (AMM), with no faults found. Embraer reviewed the brake pressure data recorded on the FDR and identified no anomalies. Non-volatile memory from the Brake Control Unit and Central Maintenance Computer was downloaded, with no recorded information identified as relevant to the event. The nose wheel steering system was functionally tested per the Embraer 145 AMM. It functioned normally in response to commands from both the rudder pedal position and the tiller. The nose wheel steering disengage buttons on each control wheel worked properly and disconnected the nose wheel steering when activated. No anomalies were noted during this testing. Many nose wheel steering components were removed and examined by the investigative group at their respective manufacturers. The Electronic Control Module, Feedback Unit Potentiometer Assembly, Feedback Unit Sensor, Tiller Assembly, Load Potentiometer, Rudder Pedal Potentiometer, and Brake Control Unit were inspected with no anomalies identified as contributing to the event. The Steering Manifold Assembly and Electrohydraulic Servo Valve (EHSV) were also removed and examined. The Steering Manifold Assembly is an electrohydraulic unit that provides fluid pressure to the steering actuator. The EHSV is a subcomponent of the Steering Manifold Assembly and converts electrical steering signals from the Electronic Control Module into hydraulic fluid flow. It applies the electrical steering signal to a torque motor, which produces a mechanical deflection of a flapper. The flapper moves to restrict fluid flow at the C1 or C2 nozzles, increasing hydraulic pressure in the corresponding circuit. The increased pressure moves a control spool, porting hydraulic fluid to turn the nose wheel left or right. During functional testing of the Steering Manifold Assembly per the Component Maintenance Manual, the flow rate through the bypass valve when open was found to be much lower than required. Upon disassembly, a flat piece of clear plastic was discovered on the bypass valve “C2” filter screen. The bypass valve opens when the steering system is disengaged, connecting the two steering actuating cylinder hydraulic chambers and allowing the nose wheel to free caster. The EHSV, P/N 22253282-103, S/N 278A, was removed and functionally tested per the manufacturer’s Acceptance Test Procedure. It passed all sections of the acceptance test. After disassembly, the C1 orifice filter seal exhibited a small area of material deformation and a small area of partial material separation. The outside diameter of the C2 orifice filter seal exhibited an area of missing material. These seals are located within hydraulic chambers that terminate at the C1 or C2 nozzles. If a nozzle becomes blocked, pressure can build within the C1 or C2 chamber, causing the control spool to move and commanding the nose wheel to turn. The void remaining on the seal from the missing fragment of material was larger than the nozzle orifice. Further examination of the EHSV found that the C1 and C2 filter plug outer diameters were smaller than required for the unit’s labeled modification status. As the outer diameter of the filter plug decreases, the gap between the filter plug and the filter bore increases. The orifice filter seal seats against this gap. Per the EHSV manufacturer, as this gap increases, so does the tendency of the corresponding orifice filter seal to extrude. For this reason, the correct outer diameter of the filter plug is considered critical to preventing premature deterioration of the orifice filter seals. ## Maintenance and Operational History ExpressJet performed a historical records search for write-ups and component replacements related to the nose wheel steering on the incident aircraft for the two months prior to the incident. No items were identified in the search. Regarding the landing gear in general, the Landing Gear Electronic Unit was replaced on July 31, 2011, due to an air/ground failure after takeoff. The nose wheel steering manifold assembly was installed on the aircraft on October 4, 2010. During the incident flight, the APU Starter generator was deferred per the Minimum Equipment List 24-34-01-2.