Narrative:

Pulling into the gate with gate services provided, I noticed 2 ramp agents, one ready to apply ground power, and 1 marshaller. After stopping at the gate, with #2 shut down, looking inside to see if we have power, looking outside at the marshaller, looking inside for power, looking outside to make sure jetway is moving, etc, I end up with both engines shut down and ground power applied. The marshaller gives me a sign and gets down off the tug. I released the brakes, and feel the aircraft move, so I immediately reapply the brakes. I may have felt the aircraft move between the chocks, but after thinking about it for a week, I think he gave me a hold brakes sign and then left my sight to put the chocks in. It is common for 2 ramp agents to catch an airplane using gate services. I don't know if they have a specific order to accomplish the many tasks, but in most places if the chocks were applied first, the jetway would be stopped and power applied without any additional delay. As for my own actions, there is no excuse for releasing the brakes without the appropriate signal, so I leave the parking brake set until it's time to release it for push. I know it was common practice to release the parking brake every leg after the chocks were in, supposedly for brake cooling, but if this is going away with the new checklist, I think this would be a good time to change the procedure, especially since the gate services block in is a busy evolution, still seen only as an exception. If there is a valid reason to release the brakes on a through flight could you let us know what it is?

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Original NASA ASRS Text

Title: A B737-300 PIC RELEASES THE PARKING BRAKE AT THE GATE PRIOR TO WHEEL CHOCK INSTALLATION BY THE GND CREW AT ZZZ, US.

Narrative: PULLING INTO THE GATE WITH GATE SVCS PROVIDED, I NOTICED 2 RAMP AGENTS, ONE READY TO APPLY GND PWR, AND 1 MARSHALLER. AFTER STOPPING AT THE GATE, WITH #2 SHUT DOWN, LOOKING INSIDE TO SEE IF WE HAVE PWR, LOOKING OUTSIDE AT THE MARSHALLER, LOOKING INSIDE FOR PWR, LOOKING OUTSIDE TO MAKE SURE JETWAY IS MOVING, ETC, I END UP WITH BOTH ENGS SHUT DOWN AND GND PWR APPLIED. THE MARSHALLER GIVES ME A SIGN AND GETS DOWN OFF THE TUG. I RELEASED THE BRAKES, AND FEEL THE ACFT MOVE, SO I IMMEDIATELY REAPPLY THE BRAKES. I MAY HAVE FELT THE ACFT MOVE BTWN THE CHOCKS, BUT AFTER THINKING ABOUT IT FOR A WK, I THINK HE GAVE ME A HOLD BRAKES SIGN AND THEN LEFT MY SIGHT TO PUT THE CHOCKS IN. IT IS COMMON FOR 2 RAMP AGENTS TO CATCH AN AIRPLANE USING GATE SVCS. I DON'T KNOW IF THEY HAVE A SPECIFIC ORDER TO ACCOMPLISH THE MANY TASKS, BUT IN MOST PLACES IF THE CHOCKS WERE APPLIED FIRST, THE JETWAY WOULD BE STOPPED AND PWR APPLIED WITHOUT ANY ADDITIONAL DELAY. AS FOR MY OWN ACTIONS, THERE IS NO EXCUSE FOR RELEASING THE BRAKES WITHOUT THE APPROPRIATE SIGNAL, SO I LEAVE THE PARKING BRAKE SET UNTIL IT'S TIME TO RELEASE IT FOR PUSH. I KNOW IT WAS COMMON PRACTICE TO RELEASE THE PARKING BRAKE EVERY LEG AFTER THE CHOCKS WERE IN, SUPPOSEDLY FOR BRAKE COOLING, BUT IF THIS IS GOING AWAY WITH THE NEW CHKLIST, I THINK THIS WOULD BE A GOOD TIME TO CHANGE THE PROC, ESPECIALLY SINCE THE GATE SVCS BLOCK IN IS A BUSY EVOLUTION, STILL SEEN ONLY AS AN EXCEPTION. IF THERE IS A VALID REASON TO RELEASE THE BRAKES ON A THROUGH FLT COULD YOU LET US KNOW WHAT IT IS?

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.