A321 flight crew reported the tow bar became disconnected during push back resulting in a temporary loss of control and the aircraft rolling over the disconnected tow bar.
Synopsis
A321 flight crew reported the tow bar became disconnected during push back resulting in a temporary loss of control and the aircraft rolling over the disconnected tow bar.
Narrative
We called for push back and received clearance onto the taxiway. Push back seemed normal and we were cleared to start engines. As we started the approximately 45 degree turn onto taxiway from gate; there was a popping sound and the push crew stopped. The sound was noticeable; but sometimes during push backs there are pops; creaks and groans; especially as the tug turns the aircraft. After a brief pause; the push continued. As we pushed onto the taxiway; we came to a stop and then began to be pulled forward to straighten the aircraft onto the taxiway. As we were being pulled forward the tug operator said 'set brakes which seemed odd as we were moving forward significantly and setting the parking brake would not be safe. Procedurally; 'set brakes' is said when the push back is complete and the aircraft is stopped. The tug operator followed with 'disconnected'. I braked hard; because I could not see the tug location and we were still moving forward. The tug was on the aircraft's right side and in danger of being struck by the right engine.We were later informed that 4 bolts had failed and sheared off of the tongue of the tow bar latch; which allowed the airplane to release. The tug had started to pull the aircraft forward and as this happened; the airplane was slung forward with momentum. As I braked; the airplane stopped but it was also rolling on or up the tow bar. The combination of the abrupt stop and the roll up and off the tow bar made the stop feel quite violent and jarring. The stop flung the Flight Attendants (FAs) forward and some of them were injured. The paramedics were called for FA number 5 position. FA number 1 position said that they twisted their ankle and hurt their wrist which was becoming swollen. They went home. Other Flight Attendants also claimed injury; but decided to continue and I don't know their details. We stopped on the taxiway. I made a PA to the passengers. I checked in with the Flight Attendants. Maintenance was called. They came out and told us to return to the gate. I made an approximately 75 degree left turn to align with the gate and then proceeded forward and everything seemed normal. At that point; the aircraft began to drift left and would not respond to steering. The nose wheel steering disconnect amber ECAM had illuminated. I stopped the aircraft. After a moment; the wing walker on the right wing came over and pulled the pin out and held it up so we could see it. The amber ECAM was gone; so I proceeded to the gate. Broken tow bar. Perhaps a novice tug operator? The tug operator used non standard terminology. Poorly defined procedures for tow bar breaks and disconnects. The current broken tow bar directive is for the tug operator to say 'brakes'. Shouldn't it be something more unique and alarming from standard callouts like 'breakaway!' A unique and alarming callout from the tug operator such as breakaway! would be more effective than the current directive of 'brakes'. The push tugs should have tall poles; so the flight crews always know the tug's location. All aircraft should have safety videos rather than safety demos; so the Flight Attendant can remain seated for push and taxi."
Second reporter narrative
After normal initialization and cockpit preparation; we called for push back and were told to push onto taxiway 1 by Ground. The tail of the plane entered the taxiway normally and the tow tractor began to turn the tail on taxiway 1. Somewhere during the turn; the tractor driver cleared us to start engines; so I began to start engine 1. Midway through the turn; approximately 45 degrees into the 90 degree turn; we heard a noticeable 'thunk' noise in the vicinity of the nose wheel/tow-bar. The push back stopped momentarily with the aircraft at approximately a 45 degree angle to the taxiway. I wasn't overly concerned about the noise since it isn't uncommon to hear noises during push back. After the momentary pause; the push back continued without word from the ground crew. The rearward push back stopped slightly off center of the taxiway; which again; is normal as the tractor driver usually straightens out the aircraft on the pull forward.After a slight pause; I felt what seemed like a normal acceleration of an aircraft being pulled forward under tow. I believe the #2 engine was still spooling up and the #1 engine was at idle. Instead of straightening out; the forward momentum of the aircraft carried us at an approximately 10-15 degree angle off center line in the direction of the gates. This struck me as odd; but sometimes tractor drivers will leave us at odd angles; so I didn't question it. Shortly after the forward momentum started; the tug driver said 'set brakes.' The aircraft was still in motion; which is very abnormal; so I shifted my attention to the Captain's feet and hands to ensure that they saw the forward momentum and used the pedal brakes rather than the parking brake to arrest the momentum. As I saw their feet move from the floor to the pedal brakes and that they weren't applying the parking brake; I heard a statement from the tractor driver that included; 'Disconnected.' I'm not sure what else was said; but 'Disconnected' caught my attention and that's when I first realized we were no longer under positive control of the tow tractor. The Captain applied the pedal brakes and we came to an abrupt halt. After stopping I looked out my right window and saw that the tow tractor and tow bar were behind the nose of the aircraft to my right.The stop was abrupt; which I assumed was due to the rapid application of pedal brakes; but later learned that as the Captain applied brakes; the aircraft impacted the tow bar causing an abrupt halting of forward momentum. The Flight Attendants were preparing the cabin for departure and at least 2 were injured during the abrupt stop. We contacted Ground to let them know we had an unplanned tow-bar disconnect and needed to remain stationary until maintenance could inspect the plane. We also contacted maintenance to coordinate the inspection. After the inspection; we were directed on Ops/Maintenance frequency to taxi back to the gate for further inspection. We both understood that we may have damage to the nose wheel and talked about our plan of slowly gaining forward momentum; then slowly turning left back towards the gate; being prepared to stop at any moment. The Captain executed that plan and turned back towards the gate. There were no cockpit indications that we had an issue; and the disengaged ECAM message was not displayed. The aircraft was slightly past the lead in line; so we had to overshoot the lead in line; then come back right to center the aircraft up. The left turn to the lead in line went smoothly; but as the Captain turned back right to center the aircraft; the nose wheel steering was unresponsive. They smoothly applied the brakes and began signaling to the ground crew that we'd be shutting down engines and needed to be towed back to the gate. At this point; I noticed that the disengaged ECAM had illuminated.I called Ops to let them know we'd lost nose wheel steering and would need to be towed in. At this point; I looked to my right as the wing walker approached the aircraft; disappeared under the nose and re-appeared holding the bypass pin high in their hand. Looking back in the cockpit; the disengaged ECAM was no longer displayed. I pointed out to the Captain that the ECAM message was gone and that the wing walker appeared to now be holding the bypass pin high in their hand; so we tried again and taxied back to the gate with no further issues. I'm not sure what caused the tow bar to break; the pushback felt smooth and controlled into the initial turn. The non-standard 'Set Brakes' call from the tow tractor driver as the aircraft was moving led to some confusion in the cockpit; but did not contribute to the rapid deceleration that led to the flight attendant injuries. Not directly a causal factor; but a standard phraseology for an uncommanded tow bar disconnect would have prevented some confusion.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.