B767 flight crew reported a loss of brake pressure and uncommanded movement while parking. Control was regained; and chocks were put in place.
Synopsis
B767 flight crew reported a loss of brake pressure and uncommanded movement while parking. Control was regained; and chocks were put in place.
Narrative
When parking at remote parking stand XX in ZZZZ; I set the parking brake but saw neither the park brake" light nor the EICAS "parking brake" advisory message illuminated. The handle did remain up; the brake pedals did remain engaged; the brake pressure was normal and the aircraft was not moving. I released and reset the parking brake a couple of times trying to also get the normal indications; which I did not get. The fact that all felt normal led me to incorrectly suspect an indication problem and not a failure of the parking brakes. I told my first officers that everything felt normal and listed all the things that were normal and called for the engines to be shut down and continued with the parking flow. As we ran through the parking checklist; we noticed brake pressure dropping off abnormally and I turned on the right hydraulic pump to restore normal pressure. After turning off the pump once more; we again noticed brake pressure dropping. After a few moments of trying to understand what we were seeing; the relief pilot noticed the aircraft had started to roll backward. I tried to stop the aircraft with the brakes but that did not work because there was no brake pressure. I quickly turned on the right hydraulic pump and was able to stop the aircraft's movement. We had rolled perhaps 15 feet. I had the relief pilot call the flight attendants to make sure no one had been hurt in the cabin. Looking outside we saw that no ground equipment had yet approached the aircraft. I had the flying first officer call operations to explain that we had a parking brake failure; that the aircraft needed to be chocked; and that a tug was needed to pull the aircraft back forward. The first officer smartly suggested turning the beacon back on and I turned the seatbelt sign back on and made a brief announcement to reseat the passengers. Operations called back shortly to say that airport operations was okay with where the aircraft stopped and would not need to be repositioned. We reiterated that we were manually holding the brakes and needed the aircraft to be chocked. The remote stand was a last minute change after landing when the outbound aircraft at the terminal was late departing. There did not appear to be chocks readily available at the remote stand and the first officer and I took turns holding the brakes. Oddly; while holding the brakes with the parking brake handle stowed; we observed both the "park brake" light and the EICAS "parking brake" advisory message for several seconds. Operations then called to say that it had been decided to move the aircraft to stand XY at the terminal and a tug was enroute for the tow. We coordinated with the flight attendants to prepare the cabin for the tow. After running the pushback checklist and reviewing the tow-in checklist; the tug arrived and towed us to the new gate. When setting the brakes at the conclusion of the tow-in all parking brake indications were normal. None the less I asked the tug driver to keep hold of the aircraft until the wheels were chocked and after he notified me that the wheels were chocked; I turned off the seat belt sign and we completed the parking procedure.I should have been able to understand the situation sooner than I did. The absence of the correct annunciations was the first red flag; and I dismissed it too easily as an indication problem when all else felt normal. The abnormal decrease in brake pressure after completing the parking flow was the second red flag. I should have understood that the brake accumulator was all that was holding the brakes and when that pressure dissipated I had no brakes. It should not have taken the unintended movement of the aircraft to convince me that I had no parking brakes. Expectation bias and fatigue may have played a role; but I am enormously grateful and lucky that no one was injured and nothing was damaged. I should have held the brakes and waited for the wheels to be chocked as soon as something abnormal happened before proceeding with the rest of the parking procedure."
Second reporter narrative
Parking in ZZZ at remote stand XX the ca set the parking brake and the indication was not there on icas. The ca tried resetting the parking brake and then a normal shut down was conducted and the crew noted a rapid decrease in brake pressure. The ca reengaged the hydraulic system and started trouble shooting the parking brake. I started monitoring out the windows to detect if there is movement and listen in on the trouble shooting. Visibility was low. While the ca and fo were trouble shooting I noticed movement and called this out as we started to roll backwards. The first press of the brakes did nothing to slow the plane until the ca turned on the hydraulic pumps. We contacted ops and ramp and turned on the beacon. I think we moved maybe 10ft but with the haze it could have been 5-20feet. The ca and fo took turns on the brakes as we waited for chocks and a tug. While the brake pedals were being held the parking brake lever was now in the down position but the light and icas were indicating parking brake on. Once the tug was connected by headset we let them know of the malfunction and we were towed to gate XY. We asked that chocks be installed before the tug disconnects. The parking brake was attempted to be used again and it indicated that it was working and brake pressure did not decrease rapidly and seemed normal.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.