History of Flight
An Embraer EMB-145LR, registration N12922, operated by ExpressJet, experienced several uncommanded swerve events during multiple landing roll outs between March 19, 2013, and March 29, 2013. The uncommanded swerves were described as the aircraft pulling to the left. During each event, the crew was able to regain and maintain runway heading.
Injuries and Damage
Passenger counts were not provided by ExpressJet. No injuries were reported. No damage to the airplane occurred.
Aircraft Information
The airplane was identified as an Embraer EMB-145LR, registration N12922, serial number 145338.
Flight Recorder Data
The flight data recorder was downloaded after an uncommanded swerve event on March 28, 2013, at about 0910 eastern daylight time, during the landing roll at Jacksonville International Airport (KJAX), Jacksonville, Florida. The flight was identified as flight number 4618 and originated from Chicago O'Hare International Airport. The crew reported an uncommanded pull to the left but were able to regain and maintain heading during the event.
Maintenance and Testing
The aircraft experienced several uncommanded swerve events during multiple landings between March 19 and March 29, 2013. The swerve events could not be duplicated by maintenance. Troubleshooting during this timeframe resulted in the replacement of multiple nose wheel steering system components. On March 29, the nose wheel steering manifold assembly (P/N 308570-1007, S/N 0445B) was removed. After removal, there were no further reports of uncommanded swerving or pulling to the left on the aircraft. The manifold assembly had been installed on the incident aircraft on March 8, 2013. A review of flights from installation to removal revealed that swerving events were reported on longer duration flights.
The manifold assembly was sent to Parker Aerospace for component level testing, including cold soaking to simulate conditions experienced during longer flights. The nose wheel steering hydraulic manifold assembly was examined at the Parker Aerospace facility in Irvine, California on June 3-4, 2013. Testing revealed unexpected pressures observed at the output chambers after the unit was cold soaked. The electrohydraulic servo valve (EHSV), a sub-component of the manifold assembly, was removed for further investigation.
Testing of the EHSV occurred at the Woodward HRT facility in Santa Clarita, California on June 5-6, 2013. The pressure anomalies observed during manifold assembly tests were also identified during EHSV testing. A teardown and examination of the EHSV identified the presence of a clear gel-like substance between the armature and the coil. Laboratory analysis revealed that the substance was similar to a thermally degraded MCS-352B lubricant. Pressure gain plots showed that hysteresis improved following removal of the substance from the armature. No other anomalies were identified during the examination or teardown of the EHSV. The EHSV manufacturer indicated that there should not have been any substance in that area and that it was unknown how the substance could have gotten there.