B737 Undifferentiated or Other Model
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Distraction; Workload
Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew FLC Overrode Automation
Procedure; Human Factors; Aircraft
Sitting at the gate loading [passengers] we turned on the APU to cool the cabin. After turning on the bleed air the ground crew alerted us that the engines where starting. The crew looked at the engine instruments and the only indication of a start was N1 at 1.5 % or so. The crew also noticed both start switches in ground. The start levers where in cut off. The crew had no intention of starting the engines and where shocked to see the start switches in ground. All earlier checklist had been completed and the crew did not know how the start switches where moved to ground. The crew immediately put the switches in off. It was less than two minutes the switches would have been in ground. Make sure all checklists are completed. Also I will be doing a double check the start switches are in off before opening the app bleed valve.
[Report narrative contained no additional information].
First Officer Reported that after starting APU at the gate to cool aircraft; ground personnel report both engines starting; requiring Flight Crew to turn off APU Bleed Air and investigate; discovering both engine start switched  were left in Ground Position.