A319 air carrier crew reported uncommanded aircraft movement after pushback when starting engines; with the parking brake set due to low accumulator pressure. The Captain reset the parking brake after the second engine start which returned the pressure to normal.
Synopsis
A319 air carrier crew reported uncommanded aircraft movement after pushback when starting engines; with the parking brake set due to low accumulator pressure. The Captain reset the parking brake after the second engine start which returned the pressure to normal.
Narrative
Intercom with ground crew didn't work at the gate so we pushed back with the Captain using hand signals. During push they cleared us to start engine 1 and we did so without incident. Once they said to set brakes; I heard the Captain say brakes set" and as I was entering the load closeout info in the box; out of the corner of my eye I noticed we were rolling forward at a slow speed. At first I was thinking maybe the ground crew was pulling us forward a bit as they sometimes do; then I remembered I had heard the captain say "brakes set" and so I looked at the parking brake and noticed it was set; and I said that we were rolling forward; and as I was about to apply brakes the Captain also noticed and he applied the brakes. We both checked the brake accumulator indicator and the pressure was low and not in the green band; so I guess that's why we rolled forward.I'm not sure if the Captain checked the brake pressure indicator when he set the brakes as part of his flow; but I could have also checked it just to have a second set of eyes on it. I'm not sure why the pressure was low. After engine 2 was started the indicator returned to the green band as normal.Checking that the brake pressure indicator is in the green band should be a sufficient way to prevent this. The Captain also said he had never had that occur in his career before."
Second reporter narrative
After pushback from the gate; brakes set; tug disconnected; the FO (First Officer) asked: are they pulling us? We were; in fact; rolling forward. Brake switch was set 'on'. Accumulator pressure was low. Toe brakes were engaged and brake switch was toggled from 'on' to 'off' back to on. This was during engine 2 start which provided adequate brake accumulator pressure. Late night. Dark. Ground crew headset inoperable. Complicated pushback instructions from ramp control. Validate; validate; validate and re validate the accumulator pressure on the triple indicator.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.