B777 flight crew parked at a hardstand reported they were cleared by ground personnel to release brakes; but when they started the engines the aircraft began rolling because the tug was not yet connected.
Synopsis
B777 flight crew parked at a hardstand reported they were cleared by ground personnel to release brakes; but when they started the engines the aircraft began rolling because the tug was not yet connected.
Narrative
While waiting clearance to start; the crew chief asked me to release the brakes. I assumed we were connected to a tug and that it would be safe to do so. (On the B777-200; you cannot always see if you are connected to a tug.) We had completed all preflight checklists; including the 'Before Starting Engines.' Shortly thereafter; we received clearance from ZZZZ Delivery to start engines. We completed the normal engine start procedure; and shortly after the right engine was started; the crew chief advised us; 'The aircraft is moving.' The motion was extremely small and was undetected by all three pilots. I immediately stopped the aircraft and parked the brakes. I checked with the crew chief; asking if anyone was injured or if there was any equipment damage. He responded that no one was hurt (thankfully) and no equipment was damaged. We discussed the incident as a crew and decided to continue. Cause: In ZZZZ; we usually park at a hardstand. We often depart from the hardstand as well. I believed we were going to be tugged out of the hardstand and were connected to a tug. In the future; I will be more vigilant when parking on a hardstand and communicate with the crew chief on the procedures that will be used.
Second reporter narrative
The aircraft was on a hard stand that did not require a push back; the only one 777 ZZZZ crews encounter in our operations. Before start checklist was accomplished and the ground crew requested brake release. The Captain released the parking brake; thinking the aircraft was connected to a tug for a push back. Both engines were started and shortly afterwards the ground person informed the captain the aircraft had started to move. The Captain quickly applied brakes and set parking brake. The Captain then asked the ground person if he was ok and if the aircraft had hit anything on the ground. The ground person answered that he was ok and nothing was hit on the ground. The crew decided it was safe to continue the flight and no further problems were encountered.Cause: Brief that no pushback is needed and insure the parking brake remains set until cleared to taxi.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.