A320 flight crew reported a parking brake pressure failure during pushback resulted in an uncommanded aircraft movement and a loss of control.
Synopsis
A320 flight crew reported a parking brake pressure failure during pushback resulted in an uncommanded aircraft movement and a loss of control.
Narrative
We were cleared to push from the gate in ZZZ; I confirmed the brake was released; and the push commenced. During push back we were cleared to start engines; the FO started engine #1. The tug driver informed me the push was complete and asked me to 'set brakes'. I set the brake; and confirmed it on the upper ECAM display and verified pressure on the triple indicator; I informed him 'brake is set; clear to disconnect interphone'. The tug was disconnected and began to drive away; I was looking for a salute. The FO mentioned needing a performance date as it had started raining and a runway change. That's when I noticed that we were moving. Initially my thought was that we were getting tugged further; but that couldn't be…. I looked down; the brake was set; upper ECAM had a green PARK BRK illuminated; the triple indicator was at ZERO. Simultaneously the FO pushed the yellow electric pump; I released the brake; stepped on the toe brakes and re set the brake. All pressure on the triple indicator returned to normal. After the startle of that was over; I looked out the window and saw the ground crew off to the right of the nose holding the steering disconnect pin up and giving me a salute. If I had to guess; I would say we only moved a few feet. At this point I wanted to be sure everyone was clear of the aircraft. I called ramp and asked them to check the camera and be sure we were clear of any ground personal; they said we were. I then called maintenance and explained what happened; I was told if all indications were normal; we were to continue and monitor it. We taxied and departed for ZZZ1. The parking brake was set; and confirmed by switch position; upper ECAM display; and pressure on the triple indicator. At some point after setting the brake; all brake pressure was lost; the brake was NEVER released.
Second reporter narrative
During pushback from the gate we were cleared to start engines. I was in the process of starting engine no1 and we realized the airport has changed runway for departure. After pushback completed; I used ACARS for getting performance for Runway XXL wet conditions. I heard brake set and normal communication happening between ground crew and Capt. While I was busy with performance data for Runway XXL departure I heard Captain saying Park brake set and upper ECAM memo showing parking brakes set. At this time; we both realized aircraft movement. When I looked up at the triple gauge brake indication; I saw all pressures zero. I immediately started yellow electric pump and saw accumulator charging and showing correct pressure again. In the meanwhile; Captain had applied brakes and thereafter we rechecked the parking brakes and ensured we were at complete stop. Captain after that spoke to ramp controller to reconfirm that all ground personnel were clear of our aircraft and ramp did say that it appears all clear to him. Captain also spoke to maintenance and since we were showing all correct pressures with no ECAM we were good to proceed.It probably was a failure of accumulator pressures wherein pressures dropped to zero after brake set. For future reference I will look at the pressure gauges of triple indicator whenever parking brakes are set or released irrespective of whatever else I am doing as part of my flows or cockpit workload.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.