A321 flight crew reported that the Captain forgot to set the parking brake after disconnecting from the tug during push back and the aircraft rolled into the towbar. Aircraft was returned to the gate for maintenance action.
Synopsis
A321 flight crew reported that the Captain forgot to set the parking brake after disconnecting from the tug during push back and the aircraft rolled into the towbar. Aircraft was returned to the gate for maintenance action.
Narrative
Ramp instructed us to push from Gate XX to Spot 1. We were cleared to start both engines. I instructed my FO to start both engines. Upon reaching Spot 1; the tug driver instructed me to set the parking brake. What I can only describe as assumption bias in a task and lack of muscle memory on the Airbus as a Captain (First full month on Airbus); I completely thought the brake was set prior to clearing the driver to disconnect. I looked down for a moment to switch our INT/RAD switch to INC. Seconds later we felt the aircraft impact to towbar. I immediately looked at the parking brake switch and realized it was still off. I set the brake switch to ON and reestablished communications back with the tug driver and verified no one was injured. We then coordinated for Maintenance to come and inspect the aircraft. A logbook entry and taxied back to the gate after the inspection and maintenance authorization. I will ensure a methodical process/procedure is used to ensure consistent disconnect procedures are utilized and treat the pushback as a Sterile Flightdeck Period. This will help mitigate assumption bias in task and trap errors when changing aircraft or seat positions. Although I truly wish this event never happened; I believe the lessons learned and realization of the effects of assumption bias while performing routine task will make me a better and safer pilot.
Second reporter narrative
First leg; first day of a scheduled 5 day trip. I had no experience flying with this CA prior to this trip. After an uneventful prefight and brief; we called ramp for push from Gate XX. Initially; we were told to hold the push due to traffic in the alley. After some delay; ramp cleared us to push tail west drop point 1. During the push back and before pull to drop point 1; the ground crew cleared us to start engines; and; the Captain instructed me to do so. We also received the load closeout via ACARS around this same time. I was heads down monitoring #2 engine start; reviewing the load closeout; and entering closeout data into the FMGC as we were pulling up to drop point 1. As I was comparing our gross weight to assumed takeoff weight; I noticed the CA reach down and flip both INT/RAD switches to INT. I briefly looked down to see what he was doing and shortly after heard and felt a loud noise from the nose of the aircraft. I then saw the Captain reach down and set the parking brake. Due to accomplishing other tasks as we were stopping; I am unsure if the brake was set during tow bar disconnect or if it was set and then released at some point during the process. The ground crew stated that the aircraft had rolled into the tow bar; they were unsure if there was damage; and that Maintenance would need to come inspect the aircraft before we (or they) moved. I coordinated with Ramp to remain in place; while the CA called Maintenance. After inspection; Maintenance noted some damage to one of the nose wheel rims and stated we would need to return to gate for further action. I coordinated with Operations and Ramp for a new gate and we taxied to Gate XY without incident. The CA entered the discrepancy in the Aircraft Maintenance Logbook. After inspection; MX (Maintenance) informed us that the wheel would need to be changed before proceeding.Cause: Captain Airbus experience - recent fleet change. ~55 hours as an Airbus Captain. Afterwards; the CA mentioned the difference between the brake in the 737 vs. Airbus; so I assume there was some negative transfer. Pilot Monitoring distraction/saturation with other tasks during that time. From my experience; it is common practice to accomplish these tasks during pushback and disconnect; as there are usually less tasks then than any other time. The only time I have seen it done differently is when there is something significant involving push back or engine start such as a contaminated ramp or alternate start procedures. In the future; I will add Captain fleet experience level as a factor when determining appropriateness of task accomplishment during the push. Additionally; I will add brake actuator position and pressure to my crosscheck during disconnect. Finally; I will work to maintain a sterile cockpit during push back to minimize potential distraction.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.