B757-200
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Human-Machine Interface
Aircraft Equipment Problem Critical; Ground Event / Encounter Object
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft
After landing I performed the normal After Landing Checklist and assisted with taxi in directions. The Captain elected to single engine taxi back; so I shut down the right engine at his direction. When we pulled into the ramp; a follow-me Marshaller was waiting for us and brought us to our parking spot. I started the APU slightly late; upon the initial turn into the parking spot. At the Marshaller's direction; the Captain stopped the aircraft and then set the parking brake. I then let him know that the APU was still spooling up. After that I went heads down to start prepping the ACARS for flight close-out. A short time later; I felt movement on the aircraft; pulled my head up and noticed that the aircraft was moving forward. I simultaneously verbally requested that the Captain stop the aircraft. He stopped the aircraft abruptly and we then continued with ensuring that the parking brake was set; shutting down the engine; and beginning Engine Shutdown Checklist flows. Upon exiting the aircraft we noticed that the nose gear had hit the weight cart and was damaged. In order to formalize confirmation that the brake is set after parking we should consider creating a verbal challenge and response for the parking brake on a procedural checklist (I also fly the KC-135 and this is a challenge/response checklist item); also ensure ground personnel give visual signals that the chocks are in place. Re-design parking brake for easier use.
I was waiting for the APU to come on line before I could shutdown the left engine. I was looking up at the over head panel waiting to see the APU 'RUN' light when out of the corner of my eye; I saw that we were rolling forward. I immediately applied max manual Brakes while; simultaneously; my First Officer shouted 'stop.' We stopped abruptly. I looked down at the parking Brake and it showed it was still set. The amber parking brake light was still on but apparently somehow the parking brake was not fully Engaged.While still in the cockpit; not realizing there was damage to aircraft; I made an AML entry for the parking brake. After exiting airplane; I saw what appeared to be only slight damage to the nose gear. I discussed it with Line Maintenance. In retrospect I should have made an additional AML entry noting the damage; but this was done by the Mechanic. The positive news is that no one was injured!
A B757-200 rolled forward after parking despite all normal indications that the parking brake was set.  The nose gear struck a ground vehicle causing slight damage.