Citation V/Ultra/Encore (C560)
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
While cruising at FL430 emergency pressurization came on. Next the cabin altitude annunciator light illuminated. Cabin altitude was approximately 11;500 feet. We performed emergency checklist; notified ATC; and requested immediate descent to 10;000 feet. The decision was made to divert to [a suitable nearby airport]. While passing approximately 16;000 feet MSL the cabin altitude annunciator extinguished.  No further problems and aircraft was landed without emergency assistance.
Part 91 ferry flight to pick up passengers on the next leg. We just reached FL430; the filed altitude. A few minutes after leveling off; we both heard the Emergency Pressure Valve open [and] at the same time we saw the EMER PRESS annunciator. It came on and off intermittently. The airplane cabin altitude rose rapidly. I remember seeing the Cabin altitude at 7;000 feet; and watch it rise to 11;500 feet. The CAB ALT annunciator and Master Warning lights did come on. The Pilot Monitoring put his mask on first; I held my mask to my face and monitored the radio until he finished securing his mask; then secured mine. It took a movement to talk to ATC due to radio congestion; but did get clearance down to FL260; and a few other intermediate levels. We never had to level off in our descent. In our descent; we did notice the cabin altitude maintained 11;500 feet. So; at times I did slow the rate of descent to our clearance limit; but that was relatively minimal. We were cleared to 10;000ft without interruption otherwise. At approx 16;000ft; the CAB ALT and EMER PRESS annunciators extinguished. The pilot monitoring did accomplish the QRH emergency descent. After we established our descent. We opted to land at the closest field in front of us. ATC; at times; did have a hard time understanding our radio transmissions due to the oxygen masks. We landed uneventfully.
CE-560EP flight crew reported loss of cabin pressurization at FL430. An emergency descent was executed and the flight diverted to a nearby suitable airport.