Date: 201702
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Weather elements / visibility: 10
Light: Night
Aircraft: Citation Excel (C560XL)
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Exterior Pax/Crew Door
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Diverted; General Flight Cancelled / Delayed
Contributing factors: Human Factors; Aircraft
Primary problem: Human Factors

Narrative: [Cruising] at FL390; we observed that a continuous door warning light showed on the annunciator panel (CWP). It was not flashing and no master caution light was showing. I went to check the door and I did not see any red light. I looked at the inspection window and the ball eyes and the second ball eye down was down half way on the right side; but no red light was showing.My SIC felt insecure and went back to check it and returned saying one of the balls was not centered. We descended to an altitude of FL290 and worked the checklist. After completing the checklist; I went back to check again and one of the eye balls was little bit down on the left side; but I still did not see ANY red lights ON. In my opinion; one of the locking pins was not making a connection with the sensor which would likely cause the door warning light to show up on the panel. Further; my opinion was that a safe landing could be made at our destination followed by a check to establish the reason for the door warning light indicating a potential problem.When I returned to the cockpit; we were already descending to [an alternate] and I was unaware that my SIC had already decided to land without asking me for my opinion as his PIC. I remained professional and did not override the decision to [divert and] land that my SIC made to avoid confrontation with the passengers and confusion on the radio. Having many years and thousands of hours of experience dealing with similar situations; I did not see a reason to land in this instance and inconvenience the passengers who would then have to find alternative transport.After landing; I then learned that my SIC had in fact requested clearance to land there. Following the landing; we as a crew should have diagnosed the problem which influenced my SIC decision to land. Following our arrival and while on the phone with the flight operation and maintenance personnel; to my surprise my SIC was already hiring a car for the passengers to head for [destination]. I asked the SIC where he was going. He replied he had vacatioin the next day and left without further explanation. I went back to the aircraft to start APU and the door warning light was no longer ON. The safety of the aircraft was not compromised and a safe landing [at original destination] was entirely feasible. My SIC was insecure and took matters into his hands without consulting my opinion.




Synopsis: CE-560XL Captain reported his First Officer made a decision to divert for an entry door problem without consulting the Captain.