B767 flight crew reported uncommanded aircraft movement after chocks were released. Brake application did not stop the aircraft so chocks were placed.
Synopsis
B767 flight crew reported uncommanded aircraft movement after chocks were released. Brake application did not stop the aircraft so chocks were placed.
Narrative
The airplane started moving when chocks were released. We had a flight from ZZZ to ZZZ1. The weather was VFR in both locations and the airplane had an MEL for the APU. We arrived at the plane with the air cart connected and the airplane was almost loaded so I sent for an amended release to leave early. The company responded that we should wait until normal departure time which was XA15 so we replied and acknowledged. I told the mechanic to get on the headset at XA05 since we had to do an air start and ZZZ is a power out station. My usual routine is when I sit in the seat set the parking brake. When the mechanic was on the headset I used company procedures to allow him to remove chocks and stairs from the airplane. About 30 seconds later I noticed the airplane moving very slightly. I immediately moved my feet onto the brakes but the airplane did not stop and looking at the brake pressure it was showing zero PSI. My copilot turned on hydraulics seeing the same thing; the mechanic was on the headset saying brakes and threw a chock in front of the nose tire. The airplane stopped. However the hose was pulled from the air cart. To my best recollection the parking brake was set and my copilot was sure it was set and mechanic said he saw the brake light on down at his station on the nose gear. However this situation has just been mentioned by the company to be careful when setting the brake and looking at the brake pressure so at the time I was thinking I must not have set the brake or I might have released it without realizing it. Luckily nobody was hurt and the aircraft did not sustain any damage. From now on I will be pointing to the parking brake light; EICAS message and pressure gauge whenever a checklist item is called regarding brakes or when set or release them. By taking this action I believe it should slow everything down as sometimes on the line we move through checklists too fast out of habit.
Second reporter narrative
I had a flight from ZZZ to ZZZ1 and settled in the cockpit. This had a differed APU. I did my duties as a first officer of all my cockpit checks and inspection of the back of the plane. As I was getting into the right seat I did notice was light on for the parking break was set. I did my cockpit flows and finished up my clearance. As we are ready to go; captain called downstairs to mechanic to remove the chocks stairs. As he did we noticed the plane moving. As we noticed it moving the mechanic said brakes brakes! Soon as the mechanic said brakes; I looked at the brake pressure gauge and it was 0. The captain jump on the brakes trying to stop the plane but it would not. I reached up to the hydraulic panel and turned on the pumps asap. As I did that the plane stop and the mechanic said I threw a chock on the front tire. First thing the captain ask is everyone ok. No one was hurt; and the only thing damaged was the air hose to the air cart. So the mechanic called for a new hose for the cart. Other than that no damage or no one hurt. The mechanic said; your parking light was on down on the gear. I verified with the captain that I did see the light on too. We talked about on the event on what happened. I found it unusual to see a 0 psi brake gauge. There was no 5605 hydro fluid on the ground. As a A&P I remember in my experience in different aircraft is that we found the accumulator bladder was leaking to the other side of the bladder which gave no solid pressure to the system. We turn pumps on it would go to 3000psi but you can see it slowly fade down to an approximately 900 -800 psi after shutting the pumps off. Which tells the bladder is not holding that has a crack or hole in it. It [is] sharing the fluid on both sides of the bladder. What I believe happened is once the pressure went to 0 psi it releases the brake. Nothing hold on the pressure on the brakes which release the brakes.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.