B737-700
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 491
Confusion; Situational Awareness; Communication Breakdown
Aircraft Equipment Problem Critical; Ground Event / Encounter Other / Unknown
Human Factors; Aircraft
Upon arrival in ZZZ; the Captain shut down the engines and I ran my Parking Flow. Right about then the Captain said that the ground crew was motioning that the number one engine was still running. I looked at the fuel levers and they were in cutout. I looked at the MFD (Multi-Function Flight Display) and sure enough; the left engine was still running. The Captain wiggled the fuel lever until it shut off. He then wrote it up. Earlier in the day a Ramp Agent came to the cockpit in ZZZ1 to ask the Captain if he had waited until the Captain had given the engines cut hand signal before he gave the clear to enter signal because left engine was still turning after he gave the all clear. We assumed at the time the motor was just winding down; but after what happened in ZZZ; we couldn't help but wonder if the same thing might have happened; albeit briefly; in ZZZ1.We should have asked more specific questions to the Ramp Agent in ZZZ1 to make sure we knew what he was talking about instead of assuming.
We arrived at the gate and I selected cutoff on the engine levers. I gave the engine cutoff signal to ground. The Marshaller pointed to the Number 1 engine. I saw it was still running and recycled the start lever. The engine then shut down. I called Maintenance and wrote it up in the log. The issue was resolved and the engine worked normally after that. After that; the FO (First Officer) and I were discussing it and realized on the previous leg; the Marshaller came up and asked if I had given him the shutdown hand signal before he gave the clear to enter to enter signal. I told him he had followed the correct procedure. He said the engine appeared to be running after that. We hadn't noticed that and assumed it was simply spooling down. In light of the second flight we realized he was right; but during the previous leg the engine had not continued to run as long and it shut down before we intervened.We need to confirm engine shutdown on the instruments before giving the hand signal and also ask better questions when an abnormality is pointed out to us.
B737 flight crew reported engine continued to run even after fuel control was selected to cutoff.