Cessna Citation Sovereign (C680)
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial; Flight Crew Air Transport Pilot (ATP)
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Aircraft Aircraft Damaged
Aircraft; Human Factors
After takeoff from ZZZ; we were being vectored for our climb and were kept on a speed restriction. Climbing through about 17;000 feet; the speed restriction was removed and we heard a noise coming from the cabin. Soon; we realized [the] cabin door key had been left in the door. Noise lasted only a few minutes followed by an engine whine in the left engine. There were no other secondary indications. [We] chose to land in ZZZ1 which was only 15min away. Landed without incident.
We were on hot spare in ZZZ after several days of early show times. I went to the aircraft to get some cash and return to the FBO. While I was there; my partner came out and said we have a trip. I got up front to prepare the aircraft. He came out and did his walk around and we left.We were slowed under [a] Class B [airspace] and subsequently ATC gave us a speed restriction. Once we were around FL190 and north of [the] Class B [airspace]; he gave us normal speed [and] that is when we accelerated and heard a strange noise. We discussed it for several minutes; but thought it was not a real issue at the time. Several minutes later; the noise stopped and the left engine had a deeper tone. We immediately started watching the gauges and reduced power. We kept the power reduced and continued monitoring the engine gauges and there were no abnormal indications. Then; I realized it was my key.When we did the key check; I felt my pocket as usual and felt my ear plugs thinking it was my key. It was completely my fault.For starters; I am going to hang my key on my lanyard from now on. Secondly; I will be checking the door lock from now on during preflight.
Air carrier flight crew left key in door and it may have been ingested into left engine during cruise flight.