NTSB Factual Report

On June 11, 2004, at 1003 central daylight time, an Embraer EMB-135LR regional jet airplane, N843RP, operating as Chautauqua Airlines Flight 6490 (CHQ 6490) sustained minor damage following a loss of control during the landing roll on Runway 13R at the Dallas/Fort Worth International Airport (DFW), near Dallas, Texas. The airplane was registered to and operated by Chautauqua Airlines, of Indianapolis, Indiana. The airline transport rated captain, commercial rated first officer, one flight attendant, and thirty-seven passengers were not injured. One passenger sustained a minor injury. An instrument flight rules (IFR) flight plan was filed for the Title 14 Code of Federal Regulations Part 121 scheduled domestic passenger flight. The flight originated from the Will Rogers World Airport (OKC), near Oklahoma City, Oklahoma, at 0930.

The automated surface observing station at DFW at 1019 reported winds from 200 degrees at 16 knots, visibility 10 statute miles, clouds scattered at 2,500 feet, temperature 29 degrees Celsius, dew point 22 degrees Celsius, and an altimeter setting of 29.88 inches.

The NTSB investigator-in-charge (IIC) interviewed the pilots and flight attendant. The pilots stated that the first officer was the flying pilot as they made a normal, stabilized approach to the 9,301-foot long by 150-foot wide runway. They stated that the main wheels touched down in the touchdown zone, and the nose wheel touched down on the centerline. After the nose wheel touched down, the airplane began to veer to the right of the centerline and the first officer noticed that the airplane required more left rudder than usual, and that inputs were not bringing the nose straight. The captain then assisted the first officer with the flight controls; however, adding more left rudder did not correct the veer to the right. Lastly, the captain utilized the steering handwheel in an attempt to keep the airplane on the landing surface. Just as the steering handwheel was moved to the left, the airplane veered sharply off the right side of the runway onto a muddy, grass covered safety area, stopping 156 feet from the edge of the runway. The passengers deplaned normally via air stairs and were bused to the terminal. One passenger was transported to the hospital, and treated for a whip-lash.

The airplane was examined by the NTSB investigator-in-charge (IIC) after it was recovered back onto the runway surface. With the assistance of the operator's maintenance personnel, and while powered by the airplane's APU, the NTSB IIC activated the hydraulic system, centered the nose wheel and moved the steering handwheel to the left. When the handwheel was moved to the left, the nose wheel turned to the right. When the handwheel was centered, the nose wheel remained turned to the right. When the handwheel was moved to the right, the nose wheel turned further to the right. The airplane was then moved to a hangar for electrical and hydraulic testing of the nose wheel steering system.

The steering handle potentiometer checked normally. The rudder potentiometer was difficult to center with slightly erratic readings around the center. The feedback potentiometer centered normally but had a small open reading at approximately the left 45-degree position. All potentiometers were electronically centered and the airplane was jacked. When hydraulic power was applied, the nose wheel turned slowly to the right reaching the seven-degree safety switch in approximately 4 to 5 seconds. The seven-degree switch functioned normally, cutting off hydraulic power to the system. The steering manifold was removed and replaced with a serviceable unit. The same check was then performed with normal results. The steering manifold was sent to Parker Hannifin, the manufacturer, for further examination.

Under the supervision of a Federal Aviation Administration (FAA) inspector, Parker Hannifin Aerospace performed a nose wheel steering hydraulic manifold pressure functional test and teardown, using an approved Components Maintenance Manual (CMM). First, a dielectric check was performed, and no faults were found. Functional testing was then performed. Lower pressures (30-50 psi) were initially used to prevent losing any of the contamination that may have been present within the manifold. When pressure was applied to the unit, only one valve responded to the pressure. The Electrohydraulic Servovalve (EHSV), serial number 748, was removed and replaced with a new EHSV, serial number 075A. When pressure was applied to the unit, both pressure vent valves registered the same pressure. The manufacturer continued to test the manifold assembly in accordance with the CMM and no discrepancies were found with the new EHSV installed on the manifold. The hydraulic manifold tear down reveled that all components were in acceptable condition with no contamination or discrepancies noted.

The ESHV, serial number 748, was taken to HR Textron for examination on July 1, 2004. Results from the ESHV functional test revealed the C1 orifice with no pressure, which was consistent with the Parker Hannifin hydraulic manifold functional test a day earlier. The ESHV tear down revealed damage to an o-ring and a small piece of contamination blocking the C1 valve orifice that was approximately the size of the letter "i" in the word "liberty" on a dime.

Embraer published and Operational Bulletin on April 13, 2004, "Nose Wheel Steering System Malfunction and Uncommanded Swerving Events." The intent of the bulletin was to provide operators of the EMB-145, ERJ-140, and EMB-135 airplanes with procedures to be followed in the event of uncommanded swerving during high speed taxi, takeoff and landing. One of the proceedures was to update the flight manuals to include the following:

"UNCOMMANDED SWERVING ON GROUND"

"Control the airplane using rudder command and differential brakes."

"Steering Handwheel.................................DO NOT USE"

"If unable to control the airplane, as additional action:

"Steering Disengagement Button..........PRESS"

"Consider the use of differential thrust reverser if serviceable"

Embraer also published an Alert Service Bulletin on April 6, 2004, "Landing Gear - Steering Handwheel - Decal Installation on the Glareshield Panel." The bulletin called for the installation of a cockpit decal on applicable airplanes that states the following:

"WARNING: DO NOT ACTUATE THE STEER HANDLE IN CASE OF UNCOMMANDED SWERVING OR INADVERTENT STEER INOP MSG."

The accident airplane did not have the decal installed at the time of the accident. However, the time for accomplishment of the bulletin was "within the next 150 flight hours or 4 months, whichever occurs first."

NTSB Probable Cause

The loss of pressure in Electrohydraulic Servovalve (EHSV) within the nose wheel steering manifold due to contamination in the C1 orifice of the valve, which resulted in an uncommanded turn of the nose wheel during landing rollout. A contributing factor was the pilot's improper use of the steering handwheel when attempting to correct directional control during the landing roll.