Narrative:

Upon parking at gate; I only had the left engine going; with normal approach and lead-in line tracking. I set the parking brake and gave a thumbs up to the marshaller and began my flows taking me to the overhead panel. I felt a 'bump' from the aircraft and I immediately looked back to the ground and saw the marshaller signaling me to stop the aircraft. I applied the brakes and stopped the aircraft from rolling and then noticed the parking brake had become disengaged. I reset the parking brake and learned that the aircraft had moved a few ft; climbing over the chock and stopping on another chock the ground person placed in front of the aircraft. No damage to the aircraft or injuries to any personnel. I wrote up the parking brake and also called maintenance to debrief him on the brake. I also debriefed the other outbound crew and the station maintenance. I am somewhat anal about the parking brake and go through a ritual of setting it -- I always: 1) make a conscious effort to set it without distraction; 2) look at the handle when I pull it; 3) tap it (quite hard) with my middle finger knuckle on my right hand twice so I can assure the brake is correctly set. I do this while I'm looking at it to make sure it doesn't slip back down. I did all this and was shocked that the airplane had moved with the brakes set. Obviously the brakes had come off somehow; I have no idea why or how. I simply didn't touch them. I never do and I made a conscious effort to set them correctly. This station's chocks were way too small; allowing the airplane to roll over the front one with 1 engine going at idle. They looked like they were made for a propeller airplane; not for a 200000 pound jet. The ground guy was fast acting but really took his life in his hands by messing with the chocks while the aircraft was moving. He saved the day; but risked his life unnecessarily in my opinion. Playing leapfrog with the chocks against a B757 isn't smart. Supplemental information from acn 715818: after having set the brake we were waiting for ground power. The captain always sets the brake and taps on the handle to ensure it's set. I saw him do this every leg including this time. We both then went heads down to start putting away charts while we thought the parking brake was set. The parking brake had worked fine on the previous leg and so far on this leg. This time parking brake actually released while we were heads down; and with 1 engine still running; the aircraft began rolling -- so smoothly we never felt it. Then it rolled over a small chock used for the nosewheel. Rolling over the small chock and resulting bump got our heads up and on the brakes while a very alert ground handler threw a second chock in front of us again. We had a quick stop. We were lucky no part of the aircraft struck anything and there was no damage to the aircraft. I don't know how far we rolled but we started the APU; shut down the remaining engine and we were towed back to the spot. I would guess we rolled 2-3 ft. No passenger fell on the quick stop and deplaning was normal. I had always assumed; incorrectly; if the aircraft parking brake released and started rolling; I would see it with my peripheral vision while in daylight hours and feel the movement through my seat; just like you do with a stopped car at a stop light. I never did. It was a complete surprise to both of us. Maintenance played with the brake and signed it off; without having found anything wrong. My lesson learned is start checking the parking brake myself with more pressure than a tap and stop relying on peripheral vision and basic senses to think I could notice a rolling aircraft. I can't! I would also recommend bigger chocks at sea. Larger chocks would have stopped us too. They were the smallest chocks I have seen for an airliner; perhaps 4 inches in ht. Maybe they work most of the time but with 1 engine at idle and being small and wet; we just slid right over it. One of the ramp guys said this has happened before where a plane rolled over the baby chocks. We were very lucky this time and dodged a bullet. But the funny thing is; I thought we had done everything right.

Google
 

Original NASA ASRS Text

Title: A B757-200 PARKING BRAKE DID NOT SET PROPERLY AT THE GATE. UNDETECTED BY THE CREW; THE ACFT ROLLED FORWARD UNTIL STOPPED BY A WHEEL CHOCK. INSERTED BY AN ALERT RAMP CREW MAN.

Narrative: UPON PARKING AT GATE; I ONLY HAD THE L ENG GOING; WITH NORMAL APCH AND LEAD-IN LINE TRACKING. I SET THE PARKING BRAKE AND GAVE A THUMBS UP TO THE MARSHALLER AND BEGAN MY FLOWS TAKING ME TO THE OVERHEAD PANEL. I FELT A 'BUMP' FROM THE ACFT AND I IMMEDIATELY LOOKED BACK TO THE GND AND SAW THE MARSHALLER SIGNALING ME TO STOP THE ACFT. I APPLIED THE BRAKES AND STOPPED THE ACFT FROM ROLLING AND THEN NOTICED THE PARKING BRAKE HAD BECOME DISENGAGED. I RESET THE PARKING BRAKE AND LEARNED THAT THE ACFT HAD MOVED A FEW FT; CLBING OVER THE CHOCK AND STOPPING ON ANOTHER CHOCK THE GND PERSON PLACED IN FRONT OF THE ACFT. NO DAMAGE TO THE ACFT OR INJURIES TO ANY PERSONNEL. I WROTE UP THE PARKING BRAKE AND ALSO CALLED MAINT TO DEBRIEF HIM ON THE BRAKE. I ALSO DEBRIEFED THE OTHER OUTBOUND CREW AND THE STATION MAINT. I AM SOMEWHAT ANAL ABOUT THE PARKING BRAKE AND GO THROUGH A RITUAL OF SETTING IT -- I ALWAYS: 1) MAKE A CONSCIOUS EFFORT TO SET IT WITHOUT DISTR; 2) LOOK AT THE HANDLE WHEN I PULL IT; 3) TAP IT (QUITE HARD) WITH MY MIDDLE FINGER KNUCKLE ON MY R HAND TWICE SO I CAN ASSURE THE BRAKE IS CORRECTLY SET. I DO THIS WHILE I'M LOOKING AT IT TO MAKE SURE IT DOESN'T SLIP BACK DOWN. I DID ALL THIS AND WAS SHOCKED THAT THE AIRPLANE HAD MOVED WITH THE BRAKES SET. OBVIOUSLY THE BRAKES HAD COME OFF SOMEHOW; I HAVE NO IDEA WHY OR HOW. I SIMPLY DIDN'T TOUCH THEM. I NEVER DO AND I MADE A CONSCIOUS EFFORT TO SET THEM CORRECTLY. THIS STATION'S CHOCKS WERE WAY TOO SMALL; ALLOWING THE AIRPLANE TO ROLL OVER THE FRONT ONE WITH 1 ENG GOING AT IDLE. THEY LOOKED LIKE THEY WERE MADE FOR A PROP AIRPLANE; NOT FOR A 200000 LB JET. THE GND GUY WAS FAST ACTING BUT REALLY TOOK HIS LIFE IN HIS HANDS BY MESSING WITH THE CHOCKS WHILE THE ACFT WAS MOVING. HE SAVED THE DAY; BUT RISKED HIS LIFE UNNECESSARILY IN MY OPINION. PLAYING LEAPFROG WITH THE CHOCKS AGAINST A B757 ISN'T SMART. SUPPLEMENTAL INFO FROM ACN 715818: AFTER HAVING SET THE BRAKE WE WERE WAITING FOR GND PWR. THE CAPT ALWAYS SETS THE BRAKE AND TAPS ON THE HANDLE TO ENSURE IT'S SET. I SAW HIM DO THIS EVERY LEG INCLUDING THIS TIME. WE BOTH THEN WENT HEADS DOWN TO START PUTTING AWAY CHARTS WHILE WE THOUGHT THE PARKING BRAKE WAS SET. THE PARKING BRAKE HAD WORKED FINE ON THE PREVIOUS LEG AND SO FAR ON THIS LEG. THIS TIME PARKING BRAKE ACTUALLY RELEASED WHILE WE WERE HEADS DOWN; AND WITH 1 ENG STILL RUNNING; THE ACFT BEGAN ROLLING -- SO SMOOTHLY WE NEVER FELT IT. THEN IT ROLLED OVER A SMALL CHOCK USED FOR THE NOSEWHEEL. ROLLING OVER THE SMALL CHOCK AND RESULTING BUMP GOT OUR HEADS UP AND ON THE BRAKES WHILE A VERY ALERT GND HANDLER THREW A SECOND CHOCK IN FRONT OF US AGAIN. WE HAD A QUICK STOP. WE WERE LUCKY NO PART OF THE ACFT STRUCK ANYTHING AND THERE WAS NO DAMAGE TO THE ACFT. I DON'T KNOW HOW FAR WE ROLLED BUT WE STARTED THE APU; SHUT DOWN THE REMAINING ENG AND WE WERE TOWED BACK TO THE SPOT. I WOULD GUESS WE ROLLED 2-3 FT. NO PAX FELL ON THE QUICK STOP AND DEPLANING WAS NORMAL. I HAD ALWAYS ASSUMED; INCORRECTLY; IF THE ACFT PARKING BRAKE RELEASED AND STARTED ROLLING; I WOULD SEE IT WITH MY PERIPHERAL VISION WHILE IN DAYLIGHT HRS AND FEEL THE MOVEMENT THROUGH MY SEAT; JUST LIKE YOU DO WITH A STOPPED CAR AT A STOP LIGHT. I NEVER DID. IT WAS A COMPLETE SURPRISE TO BOTH OF US. MAINT PLAYED WITH THE BRAKE AND SIGNED IT OFF; WITHOUT HAVING FOUND ANYTHING WRONG. MY LESSON LEARNED IS START CHKING THE PARKING BRAKE MYSELF WITH MORE PRESSURE THAN A TAP AND STOP RELYING ON PERIPHERAL VISION AND BASIC SENSES TO THINK I COULD NOTICE A ROLLING ACFT. I CAN'T! I WOULD ALSO RECOMMEND BIGGER CHOCKS AT SEA. LARGER CHOCKS WOULD HAVE STOPPED US TOO. THEY WERE THE SMALLEST CHOCKS I HAVE SEEN FOR AN AIRLINER; PERHAPS 4 INCHES IN HT. MAYBE THEY WORK MOST OF THE TIME BUT WITH 1 ENG AT IDLE AND BEING SMALL AND WET; WE JUST SLID RIGHT OVER IT. ONE OF THE RAMP GUYS SAID THIS HAS HAPPENED BEFORE WHERE A PLANE ROLLED OVER THE BABY CHOCKS. WE WERE VERY LUCKY THIS TIME AND DODGED A BULLET. BUT THE FUNNY THING IS; I THOUGHT WE HAD DONE EVERYTHING RIGHT.

Data retrieved from NASA's ASRS site as of January 2009 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.