US Airways Flight 1825

The crew reported that the flight was normal until the landing gear handle was selected down during final approach when they received a landing gear amber caution and red warning messages on the Engine Indication & Crew Alerting System (EICAS). The flight crew accomplished the applicable Quick Reference Handbook checklist items, including the Alternate Landing Gear Extension checklist. They then performed two low passes of the control tower, which confirmed the nose landing gear was not extended. The crew then accomplished the Partial Gear Up Landing Preparation checklist and landed with the nose gear retracted. After landing the captain called for an evacuation after the cockpit filled with smoke.

Post accident examination of the airplane found substantial damage to the lower forward fuselage that included abraded and missing skin. The nose landing gear (NLG) was found rotated and jammed within the nose gear bay. The nose landing gear and several other components were removed for examination and testing. There were no faults found to the nose wheel steering hydraulic manifold and selector valve, and proximity sensor electronic module.

The nose wheel steering control module (NWSCM) was also removed for download and testing. The NWSCM nonvolatile memory (NVM) indicated that there were numerous drift monitor activations after takeoff and continued after the nose landing gear was retracted. (The drift monitor keeps the nose gear at an electrical neutral position [i.e. centered] during the time between nose gear liftoff and when the gear is stowed.) The NVM flight history data recorded a NWSCM failure approximately 37 minutes after takeoff during the accident flight. Following the NVM download, an acceptance test was performed on the NWSCM with no faults found. Review of maintenance records showed that the NWSCM was installed 11 months prior to the accident to comply with a manufacturer Service Bulletin. The installation procedures required maintenance personnel to rig the steering feedback sensors (0 degrees ± 1 degree) after installation and then to record the rigging values in the Central Maintenance Computer on the airplane's multi-function display in the cockpit. This task was stamped as accomplished in the airplane maintenance records. Although the NWSCM NVM flight history data matched the installation date in the maintenance records, there was no rigging data saved in the NVM, likely indicating that the rigging process was improperly completed.

On the accident flight, the nose gear retracted normally after takeoff and then, about 37 minutes after takeoff, an undetermined fault occurred in the NWSCM and it failed to reach a “safe” mode condition. Because the nose gear steering feedback sensors were not rigged properly when the NWSCM was installed, a drift monitor steering command remained active as the "last command." When the flight crew commanded the landing gear to extend during the approach, the steering hydraulic pressure became active and the NLG rotated, responding to the "last command" from the NWSCM. This rotation resulted in the NLG becoming jammed in the nose landing gear bay, which prevented it from extending. The flight crew conducted the appropriate checklists, however, no inflight actions would have resulted in the NLG extending prior to landing.

As a result of this accident and three other similar events, the airplane manufacturer issued two service bulletins in July 2016 to upgrade the NWSCM to address the failure scenario.

Verbatim NTSB analysis and probable cause from the NTSB dataset