Citation Excel (C560XL)
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Landed in Emergency Condition; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
In level cruise; FL380; about 45 minutes from destination; we got a Yellow Master Caution and Yellow 'Cabin Door' annunciator light. We immediately pulled the Emergency QRH and went through the 'Cabin Door' inflight checklist. We followed all the items to include moving the pressurization Controller switch to manual and toggling the cabin pressure up to 9;500 ft.; selecting Passenger Safety switch to Passenger Safety On; and slowing the airplane down to 200 kts. or slower. We notified ATC that we had a pressurization issue that required we slow the plane down to 200 kts. for the duration of the flight. They were ok with this request and also gave us shortcuts to ZZZ. We did not [request priority handling].Over the next several minutes; the First Officer and I reviewed the Emergency Descent memory items; and read through the actual emergency descent checklist.I then had my First Officer don his O2 mask while I went into the cabin to let our passenger know what was going on; that we would likely arrive later than planned; and that he would need to stay seated with his seat belt secured for the duration of the flight. He understood all; and agreed with remaining belted until in the chocks. On the way back to speak with the passenger; I checked the green flags on the cabin door and all were present.A short time later; ATC gave us a descent to FL260. Shortly into that descent; the Red Master Warning and Red 'Cabin Alt' annunciator light illuminated. I immediately went into emergency descent mode; donning my O2 mask; Auto Pilot disconnect; speed brakes; igniters on; and pitching further down. Also manually dropped the cabin passenger O2 masks and turned around to signal our passenger to don his mask; which he did. While I was doing all this; my First Officer was looking at the pressurization controller and determined that the cabin pressure had increased to 10;200 ft. He toggled the manual switch down until it indicated 9;500 ft. again. While doing this; the Red 'Cabin Alt' annunciator extinguished. This all lasted only several seconds; so we decided that our next step of [advising ATC] and squawking Emergency was no longer necessary; since we had corrected the problem which triggered the Red Master Warning and 'Cabin Alt' annunciator light. Instead; I decreased the descent rate; stowed the speed brakes; igniters off; air speed to 200 kts.; removed my mask; signaled the passenger to remove his mask; and manually turned off the cabin passenger O2 flow.The rest of the flight proceeded uneventfully except for a slight ATC redirection to 'on course' during the descent since we tracked slightly off course during the few seconds that we were in Emergency Descent mode. Further communications with the passenger were made through the PA system. After landing and taxi to the ramp; passenger deplaned and thanked us for taking all the steps necessary for keeping all of us safe; and for keeping him informed.A side benefit of having deployed the cabin passenger O2 masks is that after the passenger left the airfield; we noticed that the lap child masks (that were supposed to have dropped from a door in between the middle four cabin seats facing each other) did not drop. Their door did not even open. Also; the 2 Lav masks did not drop from their stowed positions in the ceiling; even though their door did open.After speaking with Flight Control; Maintenance Control and the Chief Pilot; I completed separate maintenance write ups for the Yellow 'Cabin Door' annunciator light (which stayed on until the battery switch was turned off at ZZZ); and the 4 O2 masks which did not fall properly.This event made us aware that even though the Cessna Emergency QRH did not emphasize it; nor even mention it in a 'Note;' it is vitally important to know that when the pressurization controller is in manual mode; we need to be constantly monitoring and adjusting it to maintain proper cabin pressure throughout the flight. In the future; I willspecifically assign this task to the First Officer; giving all the reasons why this assignment is important; to include this experience. I will also continue to intermittently monitor it myself as a backup.As for the lessons learned with regard to the (4 out of 12) passenger O2 masks which did not drop properly (1/3 of our passenger masks); I am grateful that we only had 1 passenger on board for this flight; and Not full capacity plus 1-2 lap children. The latter situation could have created a liability incident for us; real or perceived. In this case; it would have been a perceived one since we actually did not have a real cabin depressurization. Unfortunately; proper dropping of the passenger O2 masks is not something that pilots are able to assess; on preflight nor otherwise. I assume that there is a rigorous Maintenance schedule for assessing this critically important function. At the very least; I would expect that Maintenance would drop the masks at some regular interval in a controlled setting. I would also hope that they would note; and keep track of; the individual A&P who restocked the masks prior to the Maintenance or pilot deployment. Since there is a human factor involved in the restocking of the masks; this could help Maintenance determine if a specific A&P needs additional training in this area. Also; a re-deployment by our best A&P re-stockers immediately after restocking could help determine if there are any mechanical issues causing a failed O2 door or mask deployment; leading to replacement of those failed parts. Again; I am certain something like this is already in place; but I felt it was important to note these concerns since we; as pilots; have no control over this process and eventual outcome when critically needed.
Citation Captain reported loss of cabin pressure that resulted in an expedited descent.