What happened
On April 14, 2015, a crew from the Aircraft Transport Unit was preparing for a medical evacuation flight from Warsaw Chopin Airport (EPWA) to Skopje (EPSC). During taxiing, the pilot performed a pre-flight check of the nose wheel steering system and discovered that the front wheel could not be steered. The co-pilot performed a secondary check, which confirmed the steering failure.
To return to the base, the captain decided to proceed using differential braking maneuvers. During these turns, the captain noted difficulty executing tight radius turns and felt vibrations originating from the nose wheel area. Upon stopping the Piaggio P1．80 Avanti II, the co-pilot inspected the steering connection and found that the pin connecting the steering system to the nose wheel had fallen out of its bushing.
The crew was able to re-establish the connection by reinserting the pin and securing it with its integral safety clip. Subsequent engine run-up checks and taxiing showed that the steering system was functioning normally, and the scheduled mission was completed without further incident.
The investigation
The investigation focused on determining why the steering pin had dislodged from the assembly. The inquiry examined the mechanical state of the steering linkage and the maintenance/pre-flight inspection procedures used by the operator.
Findings
- The primary cause of the incident was the improper installation of the pin connecting the steering actuator yoke to the strut, specifically that the pin had been inserted too shallowly into the end of the actuator yoke.
- A contributing factor was an inadequate pre-flight inspection, which failed to detect the improper seating of the pin.
Safety action
The operator has implemented several systemic changes to prevent recurrence, including:
- Updating Standard Operating Procedures (SOP) for the Piaggio P180 Avanti I and II to include a specific requirement to verify the security of the steering pin by pulling on the safety clip.
- Updating hangar procedures regarding the aircraft's movement.
- Implementing a visual indicator by painting the lower portion of the pin red; a correct installation will show the red color, while an improper installation will reveal the natural metal color.
- Utilizing red tape on the linkage to provide an additional visual check during the connection/disconnection of the steering components.