Air carrier flight crew experienced aircraft loss of control due to malfunction of parking brake. Flight crew regained control of aircraft.
Synopsis
Air carrier flight crew experienced aircraft loss of control due to malfunction of parking brake. Flight crew regained control of aircraft.
Narrative
We taxied in to Gate XXX single engine at ZZZ. After receiving the stop signal from the Marshaller; I set the parking brake and also gave the hand signal indicating I set the parking brake. I then looked up at the overhead panel; waiting for the external power to be connected so that I could turn off the remaining (left) engine. I then looked down towards the windscreen; and simultaneously with the First Officer observed that we were moving forward I immediately applied the brakes and reset the parking brake. The ground crew had to push us back approximately 8 feet. Fortunately nobody was injured and the aircraft did not strike anything. The parking brake released without my knowledge/recognition. I do not know why this unintentional brake release happened. I always try to be extremely vigilant about the movement of the aircraft around personnel and ground objects in the gate area I've always kept my feet near the wheel brakes and attempt to keep my scan outside until the engines are shutdown. In this case; my eyes were inside the aircraft waiting for the external power to be applied so that I could shutoff the remaining (left) engine. This removed my scan from outside the aircraft; which unfortunately meant I was not able to immediately observe unintended aircraft movement. When we are taxiing the aircraft; we always stress the importance of having at least one set of eyes outside the aircraft at all times to prevent a ground incursion. The same applies for operations at the gate with any engines operating. In the future; I will brief First Officers to monitor the movement of the aircraft while my eyes are inside waiting for external power to be connected. This needs to continue until the engines are shutdown AND ground personnel have authorized the release of the parking brake. I am extremely fortunate to have learned this lesson without anyone getting injured or damage occurring.
Second reporter narrative
Flight up until aircraft parking was non eventful.We pulled into Gate XXX with a slight tailwind (winds out of the west). As the aircraft slowed to a stop at the gate; the ground crew gave the signal (X") to stop. Captain (CA) complied and pulled the parking brake handle; verbally saying; "Parking brake set". I started to dim/turn off display screens and lighting on my side (head down). I returned to a visual picture questioning myself of motion. I saw the Marshaller signaling "X" for us to stop but was unaware that we were actually still creeping forward. Their motions seemed like "normal ops" compared to a hazard/emergency type (which definitely would have caught my attention). CA applied the brakes to comply with the Marshaller's signal. We were actually rolling forward though he had the "parking brake set". We took about an 8 minute delay due to the situation but the ground crew was able to push us back to the correct parking spot. We are both very thankful that neither ground personnel nor aircraft were affected.Cause: Unexpected brake release Suggestions: Verify parking brake is in fact set before heads down."
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.