CRJ-700 flight crew reported after the aircraft was shut down at the gate; the left engine started on its own possibly due to electrical power interruption related to the power cart.
Synopsis
CRJ-700 flight crew reported after the aircraft was shut down at the gate; the left engine started on its own possibly due to electrical power interruption related to the power cart.
Narrative
Upon arrival into ZZZ we shut down and the rampers connected external power via a cart. Once power was connected I double-checked the electrical synoptic page and power was normal so I shut down the APU. Soon after the lights started to flicker and the power was cut off to the airplane. The rampers plugged the power back in and I decided to start the APU again until [after] the passengers had all been deplaned. The APU started normally and soon after we heard the sound of another engine being started. Thinking it was another jet on the ramp I look outside only to realize it was our own left engine being started while there was baggage handlers unloading bags from the aft bin. I promptly rushed to hit the stop switch to stop the engine start. Neither myself nor my FO attempted the engine start.Cause of the incident was probably due to an unrelated power cart that caused a trip in the engine start sequence during power transfers.
Second reporter narrative
While deplaning in ZZZ the Captain shut down the APU while I was saying goodbye to the passengers. After shutting down the APU; the external power cart was not hooked up correctly; even though we had a green AVAIL light; and the power flickered off and on very fast continuously. The power cable then fell off because it was not connected correctly. The cabin went completely dark and we tried to get the ground crew to reconnect the power. They reconnected it; but we still had the same flickering issue. We decided to start the APU to not have to use the ground power. The APU started and I continued to say goodbye to the passengers. After about 20 seconds it sounded like a jet or something was pulling onto the ramp. I decided to look outside and noticed the left engine had somehow started. I immediately rush to the cockpit where the Captain was and he checked the thrust levers were in shut off (they were) and then he pressed the starter stop switch. This stopped the engine. We believed it started due to the constant power changes throughout the aircraft.We could only come to the conclusion that it was due to the electrical pulsing of the external power. The Captain called the duty pilot and Maintenance Control to discuss the incident. Neither had an idea of what to do.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.