A B777 FO RPTS ATTEMPTING TKOF AT JFK WITH THE PARKING BRAKE SET; AFTER A LONG DELAY ON THE RWY. FLT ATTENDANTS NOT SEATED; BUT NO INJURIES.

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WE REQUESTED RWY 31L AT KENNEDY DUE TO RWY LIMIT CONSIDERATIONS. THE ACTIVE WAS RWY 22R. TWR CLRED US ONTO RWY 31L; BUT SAID THERE WOULD BE AN APPROX 10 MIN DELAY DUE TO NEW YORK DEP FITTING US INTO THE DEP FLOW. AN ANNOUNCEMENT WAS MADE TO THE PAX THAT THERE WOULD BE A DELAY ON THE RWY. AFTER APPROX 8-10 MINS WE WERE CLRED FOR TKOF. I PRESSED DOWN ON THE BRAKES TO RELEASE THE PARKING BRAKE BUT DID NOT CONFIRM RELEASE. I RAN UP THE ENGS TO APPROX 1.10 EPR THEN ENGAGED THE AUTOTHROTTLES AS I PUSHED UP THE THROTTLES. AS THE THROTTLES MOVED FORWARD; I SENSED NO ACFT MOVEMENT AND NOTICED THAT THE PARKING BRAKE WAS ENGAGED. I DISENGAGED THE PARKING BRAKE AS THE WARNING HORN CAME QUICKLY ON AND OFF; AND CONTINUED WITH A NORMAL TKOF. LATER IN THE FLT; WE FOUND OUT THAT 2 OF THE FLT ATTENDANTS WERE OUT OF THEIR SEATS DURING THE INITIAL TKOF ROLL; AND LUNGED BACK DURING THE TKOF; BUT NO INJURIES WERE CAUSED. I THINK THE MAIN HUMAN FACTOR ISSUES INVOLVED IN MY PERFORMANCE WERE GETTING OUT OF THE NORMAL TKOF SEQUENCE WITH THE LONG DELAY AND THE LULL OF SITTING FOR 10 MINS WITH ALMOST NO RADIO CALLS AND MAINTAINING STERILE COCKPIT. ANOTHER FACTOR WAS COMING OFF A FEW WKS OF MIL FLYING; IN AN ACFT THAT HAS NO PARKING BRAKE AND A DIFFERENT ENG RUN-UP SEQUENCE. I DO NOT KNOW OR UNDERSTAND WHY THE FLT ATTENDANTS GOT OUT OF THEIR SEATS.