Citation V/Ultra/Encore (C560)
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 60; Flight Crew Total 5300; Flight Crew Type 500
Time Pressure; Distraction; Workload
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Aircraft
About 10 minutes after reaching our cruise altitude of 40;000 feet; the door seal light illuminated. I prepared for an emergency descent and asked for a lower altitude. ATC approved it and a few seconds later a loud sound was heard from the door as the pressure started escaping. I started my emergency descent down to 10;000 feet and informed ATC of my intention to divert. Upon inspection by a mechanic; it was found that condensation had built up in the door seal after heavy rain two nights before. That condensation froze and caused the seal malfunction. The water was drained; and the trip continued uneventfully.
Cessna Citation pilot reported the illumination of a cabin door seal warning light; followed by a loss of cabin pressure warning came on during cruise. A descent was executed; and a successful diversion a suitable airport was accomplished.