2023-07 · NASA ASRS report 2018695
Air Carrier A319 pilot crew reported; after push-back with parking brake set; the aircraft rolled forward; and struck the tow-bar with the nose gear. Maintenance and the pilots determined the brake accumulator pressure had failed. Captain stated seeing this issue with older A319's with only the left engine running.
After pushback; parking brake was set. During tow bar disconnect; I noticed bleed off of the accumulator pressure. I immediately depressed the brake pedals to activate normal braking. However; the aircraft had rolled slightly and the nose gear impacted the tow bar. Maintenance was called to inspect the aircraft before it was moved. Maintenance subsequently approved movement of the aircraft back to the gate and signed off the AML (Aircraft Maintenance Logbook) entry. I visually inspected the nose gear and saw that the placard located on the front of the nose gear where the tow bar hooks up was scuffed; and no other damage noted.I had been in the habit of not only checking the accumulator pressure after setting the parking brake; but also monitoring it until the ground crew disconnects the tow bar. Accumulator pressure bleed off with only the left engine operating on older A319's is a factor; but if I had monitored the pressure more closely; I could have operated the normal brakes before the aircraft started creeping forward.I have noticed on many occasions accumulator pressures dip below the green band after setting the parking brake; and while the parking brake is set with only the left engine operating. This is particularly noticeable on the older A319's. My recommendation is to periodically check the performance of the accumulators; and to issue a safety bulletin to remind aircrews of the possibility of aircraft creep during tow bar disconnect with only the left engine operating.
During pushback off Gate XX in ZZZ; we came to a full stop at the end of the push. Push crew asked the Captain to set the parking brake. Captain set the parking brake while FO (First Officer) was performing an engine start and communicated that 'the parking brake was set and you're clear to disconnect.' We did not feel anything; but the ground crew called up shortly afterwards saying the aircraft moved forward during the disconnect and hit the tow bar; causing damage to the airplane. We acknowledged the information; confirming the parking brake indicated was green on our side; but looking at the accumulator; the brakes didn't have pressure. The Captain started manually applying the brakes. Once we confirmed the area was clear; the Captain turned on the yellow hydraulic pump to charge the accumulator. The accumulator charged normally. We contacted Maintenance; keeping Operations; Dispatch; and Ramp Control aware of our situation. Eventually; Maintenance showed up; did their inspection; and we had the aircraft towed back onto the gate. We did the maintenance logbook entry for the damage after parking at the gate. I believe the brakes accumulator not being charged up was the cause of us rolling forward during push. Only suggestion I have is that we need to look at not only the parking brake message; but also the accumulator any time the parking brake is applied to make sure the system is pressurized properly.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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