Flight Crew Type 430
Communication Breakdown
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control
General None Reported / Taken
Procedure; Human Factors
About 30 minutes prior to scheduled push; I noticed a ramp crew outside pointing at the power cord and giving inquiring thumbs up. Since he did not perform the 'disconnect ground power' signal; the APU was running and bussed up; and it was so early before push; I thought he was asking if the power was good. I gave a thumbs-up and connected the ground power. About 15-20 seconds later; the Ramp Agent pulled the ground power. The APU was still running so transitioning back to APU Gen was instantaneous. About 15 minutes later; I was in the restroom and heard some insistent knocking on the aircraft. I could hear the Captain move from the galley area to the cockpit. Apparently; the ground crew had pulled the chocks and the aircraft rolled three to four feet backwards before a Ramp Agent could jump on the tug and stop it. Fortunately; no damage was done no injuries occurred but the forward service entry was partially blocked. Since the door could not be closed; the aircraft had to be towed forward to allow door closure. I am not sure when the chocks got pulled but suspect it may have happened when the power was pulled since the Ramp Agent was way out of sequence timing wise and used a completely non-standard signal when he pulled the power. We were very lucky no damage or injuries occurred. Passengers actually didn't even notice since the roll was very gentle.Have Ground Crews use standard signals for disconnecting power and pulling the chocks if not in voice communication with the cockpit. Brief the Ramp Agents on the importance of knowing the parking brake is on prior to pulling the chocks. Chock the tug and don't remove the chocks until the tug is running.
A B737 First Officer reported that ground personnel prematurely removed ground power and chocks prior to pushback.