Date: 201509
Local time of day: 1801-2400
Location: MCO.Airport, FL
Flight conditions: VMC
Weather elements / visibility: 10
Light: Night
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower MCO
Aircraft component: Parking Brake
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Fatigue; Situational Awareness
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Flight Crew; Person Air Traffic Control
When detected: Taxi
Result: Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Human Factors
Primary problem: Ambiguous

Narrative: We diverted into MCO due to weather at the planned destination. Based on ramp location and ATIS at MCO; the planned departure runway was Runway 36L. After start-up on Taxiway A; we encountered an ATC ground hold due to sequencing into [destination airport] for approximately 20 minutes. Subsequent taxi instructions; 'Taxi to Runway 36L via A; B10 hold short 36L.' After holding short for landing traffic on Runway 36L; we were unexpectedly cleared to cross Runway 36L and hold short of Runway 36R. We advised Tower we were expecting 36L but he instructed us to 36R for noise abatement. We frequently encounter runway changes (Runway 8L for Runway 8R) and have developed a good flow to quickly prepare the aircraft for departure. FO updated the FMC; confirmed takeoff data (level off and power setting); runway heading and briefed while taxiing to hold short of 36R. Prior to reaching the hold short; we were cleared to 'line up and wait 36R' but I requested a couple of minutes. Although we were both ready and aircraft was properly configured for departure; I directed the FO to pull out the QRH and review the new 'takeoff runway or performance change procedure.' We advised tower we needed a couple of minutes and was instructed to hold short of Runway 36R and I acknowledge the 'hold short.' Upon reaching the hold short line I set the parking brake and selected the Override light switch. The FO found the procedure and we ran through it confirming everything had been considered and properly accomplished. As we completed the procedure and looked outside; we and the tower simultaneously recognized we were moving. Tower instructed us to hold short; but the aircraft had crossed the hold short line by a few feet. Another aircraft on the other side of the runway (east side of B10) had received clearance for takeoff. Even though our aircraft didn't interfere with the other aircraft's path on to the runway; we had cross the 'Hold Short Line' and takeoff clearance was canceled and they had to exit the runway. We then were cleared for takeoff and departed uneventfully. I specifically recall setting the brake and turning on the override light in one motion just as we do when reaching a parking spot. I just couldn't account for how the parking brake released. However; when we arrived [at our destination]; while waiting for an outbound aircraft; I had an opportunity to set the parking brake several times on the taxiway. I discovered that with light differential pressure on the top of the rudder pedals; the parking brake would slowly release. The parking brake handle would slowly descent (release). Typically; setting and releasing the parking brake; requires a firm force and the handle snaps down with some aural feedback. I entered a discrepancy in the logbook for an inspection of the parking brake system. A couple more comments: one; fatigue may have some minor contribution after a long day. Two; provide more flexibility to the crews by changing the 'takeoff runway or performance change procedure' to a guide. This would not require a crew to review it; if the crew is familiar with the steps required to change runways. In our case; it directly contributed to the incursion because we had to stop; find the procedure and perform the steps while we were on the hold line.


Second narrative: [Report narrative contained no additional information].


Synopsis: B757-200 flight crew reported they had a runway incursion when they failed to properly set the parking brake; which may have been malfunctioning.