B757-200
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Training / Qualification; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Returned To Gate; General Maintenance Action
Human Factors; Aircraft; Procedure
Aircraft was tugged out of parking spot and started both engines - crew noticed a status message light - status message read 'L ENG PRIM CONT'.  Captain instructed First Officer (FO) to try auto/erase procedure 2-3 times with no success while Captain reviewed MEL.  Ramp Control asked us to move forward to make room for an aircraft to push; released mechanic off headset with lineman in sight and Captain taxied ahead towards spot #5.  Captain stopped aircraft; and FO called ramp control to see if we could remain at current position to troubleshoot a maintenance issue.  Permission was granted. Crew contacted maintenance control on local frequency; told them of the problem; relayed MEL number; and was told that maintenance truck was on its way and mechanic would hook up via headset.  Discussion evolved with Captain calling Dispatch on his cell phone; FO coordinating with ramp control; and Captain discussing with on-site mechanic and ultimately Maintenance Control.  On-site mechanic; Maintenance Control and Dispatch all told us fix was involved and we needed to return.  FO coordinated with ramp control; which needed us to move for an aircraft behind us so crew was instructed to proceed to the Ramp.  Captain reported our intent to Dispatch via cell phone; acknowledged and confirmed with FO that Ramp Control wanted aircraft to return.    With no lineman; Captain cleared left and got clear right verbal from the FO; who noted that the maintenance truck was outside the line.  Thrust levers were advanced to minimum breakaway thrust to initiate taxi and crew was immediately alerted by mechanic to stop aircraft since mechanic was still on headset.  Captain estimates movement of aircraft between 3-6 feet after debriefing with mechanic.  Captain and FO were met by an ACP; who asked to be briefed by the flight crew of their actions and then ACP debriefed the crew his observations and what the correct procedures for a return to blocks should have been.  Maintenance item was deferred and flight was uneventful.  Lessons learned / Procedures emphasized:  After block out and discovering a maintenance issue that I could not resolve; I should have immediately called Dispatch & discussed problem jointly with Maintenance Control.  On-site mechanic should not have been involved until aircraft was safely parked under lineman direction.  This was a busy communication coordination scenario.  All parties in this incident had best intentions to get flight safely; legally and quickly on its way.  As discussed; we luckily avoided injury to the mechanic that was on headset.  To avoid a potential mishap; following the procedure put in place for an unresolved maintenance issue after block out; getting back safely into a parking spot under the direction of a lineman with wing walkers would have mitigated the risk of a potential injury and/or accident to ground crew or equipment that are not visible to the flight crew.  For me personally; this incident has re-emphasized the importance of this procedure.  It might also be important to emphasize to on-site maintenance crews that they are not authorized to approach aircraft after block-out.
We pushed back and started both engines normally. After the start; we got a L ENG PRI CONT status message. The mechanic was still connected and we told him what we had. I tried to clear the message but it would not clear. Ramp then told us to move to the front line because another plane needed to push. The mechanic disconnected and we taxied to the front line. I think the mechanic talked to maintenance; and reconnected with us at the front line. We were working on the problem and we were talking to ramp; Dispatch with maintenance; the plugged in mechanic and eventually ground. We were told to go down to ramp 11 to work on the problem. I contacted ground and was given clearance to taxi. We had no marshalling at this point and the Captain said clear left and I looked and it was clear right. The maintenance truck was parked outside the line where it should be and we had a clear path to taxi. I remember hearing the parking brake handle go down; then ramp and the mechanic say stop; and then the Captain used the brakes to stop. It all happened within a few seconds. The mechanic was still plugged in. He disconnected and we taxied down to the ramp. The ACP (Chief pilot) met us at the ramp and talked to us about the situation. He went over the procedures and gave us good information on how to prevent this from happening again. Once we pushed back and had both engines started; the mechanic should have been cleared off and we should immediately call Dispatch with maintenance. The mechanic should not have been involved with this until we were parked at the gate again. We should coordinate with ramp where they would like us to go work the problem. In this situation; we should have made sure the mechanic was off the headset and clear of the airplane. With no marshalling at the front line at this point; we could have asked ramp if we were clear around us after working the problem so we could taxi off the ramp.
When a maintenance issue develops after engine start; a Mechanic is called; and plugs-in a headset. It is decided that the aircraft needs to return to the parking space; so the Captain  forgetting the Mechanic is still plugged in; mistakenly attempts to begin taxiing. The Mechanic quickly announces his presence and the aircraft is stopped with no injuries.