Cessna Citation Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 35; Flight Crew Total 7500; Flight Crew Type 2000
Troubleshooting
Aircraft Equipment Problem Less Severe
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
After departing and enroute to [our destination] we had a 'door not locked' warning light illuminate. This was followed by a 'cabin 10;000 feet' warning. This occurred at approximately 9;500 feet MSL. We immediately stopped the climb and advised Center of the problem. They assigned us a lower altitude. We then requested vectors to the nearest suitable airport.We made an uneventful landing [at the nearest airport.]Upon investigation we discovered there were 2 green indicators flags that were not aligned perfectly. Aligned; but a fraction from perfect. It appears that this also allowed the cabin to 'climb'.We re-filed; loaded the passenger; and triple checked for perfectly aligned indicator flags after securing the main cabin door.Continued to [our destination] and landed without incident.Everyone should carefully check the main door green flags for 'perfect alignment' before beginning the taxi roll. They must be perfect! Especially flying older airplanes.
The flight crew reported illumination of a 'door not locked' warning light; followed by inability to control cabin pressurization. They diverted to the nearest suitable airfield; corrected the problem; and continued uneventfully to their destination.