Citation II / V / Ultra - Pressurization System

[@ZaphodsPlanet]

Out of curiosity, what does the system do if it senses you start to loose cabin pressurization at say 30K ft?

[@citationpro]

Since so many people are curious about the recent crash of a Citation V, I'll limit my description to specifically the V and Ultra. The Citation II and Encore have significant differences from this description... Several things will occur. Obviously the climbing cabin altitude would be reflected in the cabin pressure gauge to the left of the pressurization controller. As the cabin climbs above 10,000 feet, the CAB ALT red annunciator will illuminate and trigger a flashing MASTER WARNING light in front of each pilot. The MASTER WARNING light has a noticeable "clacking" sound, but there are no other audible chimes or buzzers. The pressurization system has what are known as cabin altitude limit valves built into the system. These limit valves are designed to close the outflow valves if cabin altitude exceeds 13,000 feet +/- 1500 feet. If the cabin altitude exceeds 13,500 feet +/- 600 feet, an automatic system should cause the passenger oxygen masks to automatically deploy. The passenger oxygen masks are not satisfactory for continuous use above 25,000 feet. Several things could inhibit these processes. The loss of normal DC electrical power (such as a dual generator failure and switching to EMER bus) would prevent the CAB ALT / MASTER WARNING from illuminating. A loss of normal DC electrical power would also prevent the masks from automatically deploying (it relies on an electrical sensor to determine cabin altitude) as well as if the system switch were placed in "Crew only" rather than "Normal." A completely empty oxygen bottle would also render the system inoperative and useless. The cabin altitude limit valves would be ineffective if the pressurization source selector were to be placed in the OFF or GND position in flight. In other words, they would close the outflow valves, but with no air incoming to the cabin, the cabin would remain unpressurized. Obviously this all depends on a properly maintained and inspected system as well. Without maintenance and inspection, all bets are off. Lights may be burned out, wires disconnected, valves sticky, etc. Please let me know if you'd like further explanation of any details.

[@ZaphodsPlanet]

@@citationpro Thanks so much for the explanation man. Yes this was in regards to what might have occurred to those poor people in VA. It was a pretty old Citation, a 1990 model 560. I don't know which model information would carry on beyond that as it's been eons since I worked at an FBO when I was slightly more familiar with such things. Are newer planes any more "automated".... as in... if cabin altitude went above 13000ft the autopilot might automatically lower aircraft to like 8000 ft? Back in 1990 things weren't as advanced as now but I'm curious. Although I can't afford it at the moment there have been times when I've toyed with the idea of getting a private pilot's lic. But every time I see an accident like this whereby a single pilot may have screwed up and forgot to toggle a switch or maintenance wasn't kept up with.. it just scared the hell out of me and I think the only way would be if by some act of the guy upstairs I had enough to buy a new jet and hire two competent, unjabbed professional pilots. Old planes kinda scare the crap out of me, as do lackadaisical pilots. Anyway, thank you again for taking the time to write out what you did.

[@citationpro]

@@ZaphodsPlanet , no problem, I enjoy talking about these systems. Newer planes are definitely more automated. The Citation XLS equipped with Garmin G5000 avionics has an "emergency descent mode" from which the autopilot will automatically command a descent to 15000 feet if the cabin altitude climbs above 14000 feet while the aircraft is flying above 30,000 feet. Of course this sort of automation has only come about within the past 10-15 years and is only available on fairly "high end" aircraft. A person must consider there is no such thing as perfect safety, only "safe enough" for the situation at hand. In a perfect world, we'd only fly brand new multi-engine jets with highly trained, highly experienced, perfectly rested, perfectly fit pilots, during beautiful weather conditions, to long runways at airports with all kinds of services available, for the price of $1/hour. Of course we don't live in that world. We mitigate risks as best as we can, knowing that at some point we will bump up a constraint related to time, money, and/or technology. If you have the opportunity to fly, I think you should take it. The benefits usually outweigh the risks.

[@ryanmcfarland6086]

This entire video compellation on the 500 series is excellent. Well done!

[@andrewletaev2097]

Great description. Many many THANKS, Sir !

[@matheusribeiro2568]

Great overview! Good job!

[@TIO540S1]

Well done. I don’t fly a Citation,I fly a C441 but the system, concepts, and procedures are pretty much identical.

[@citationpro]

I have several hundred hours in 402s and a handful of hours in twins like the 310. When I first got in to the Citations, it amazed me how similar the Citations are to twin Cessnas. I've really enjoyed flying Cessna products.

[@Invertatude]

Really appreciate the videos thanks!

[@WorldPeace-AdamNeira]

What warning signals/sounds/lights are activated for the pilot in the case of depressurisation on a Cessna 551 Citation II (Single Pilot)? Hope to receive an answer from you soon.

[@citationpro]

Hi, great question. I've never flown the 551 specifically, but assuming it's like the other 500 series Citations, it would have a red "CABIN ALT" annunciator in the upper left corner of the annunciator panel. This would illuminate if the cabin altitude reaches 10,000 feet or higher. It would also trigger the red flashing Master Warning lights directly in front of both the pilot and copilot. There would not be an audible alarm, but the flashing Master Warning lights are hard to miss.

[@WorldPeace-AdamNeira]

@@citationpro Thank you for your reply. I was asking the question as part of my investigation into the 20.37 (EEST) The Baltic Sea, Latvian Territorial Waters, 23 kms NW of Ventspils, Cessna 551 Citation II (Single Pilot) OEFGR Light Plane Crash. I have a very large file on the case. I've been auditing the global aircraft: fixed and rotary wing accident landscape in depth since May 2021.

[@kbrod7]

Any insight on what may have went wrong with the V that supposedly depressurized yesterday?

[@citationpro]

Great question and I have nothing to add beyond what has already been reported in the news. I'm sure investigators will get to the bottom of it. Once a report is issued, I'd be happy to offer further insight if you have questions about certain details from the report.

[@goutvols103]

Thank you for sharing. Understanding that this is somewhat off topic, but are you able to explain what happed on that Helios flight in which the pressurization switch was set to Manual and during preflight, it was missed. What alarms would be initiated to inform the cockpit of an issue? Thanks in advance.

[@citationpro]

Great question. I can't speak to the exact systems used in 737 aircraft like what Helios flew, but in all pressurized aircraft there would be multiple warnings under most circumstances. Warning lights, sounds, and the masks automatically dropping from the ceiling among those. I don't have a good explanation for why the Helios crew made so many mistakes.

[@김순미-d2m]

I would like to know about the following information for the Cessna 560 aircraft. List what the main hydraulic system power. I'd appreciate it if you could tell me where I can find the information about this. Thank you.

[@citationpro]

In the Citation 560 (V, Ultra, and Encore) the main hydraulic system provides power to extend and retract the landing gear, flaps, speed brakes, and thrust reversers. Unfortunately there isn't much information about these systems online. The closest I've been able to find is the flight manual for the Citation Bravo at Smartcockpit.com. This would basically be the same as the 560 aircraft, except the Bravo has electric flaps rather than hydraulic. www.smartcockpit.com/aircraft-ressources/CESSNA_Citation_Bravo-Hydraulics.html If you have any other questions, I'd be happy to answer them.

[@tbainbrid]

So, I had my first right seat up to FL340 in a Citation 550 II last weekend. i watched the PIC control to .500 descent, but looking back, didn't pay attention to when this occurred. We were descending into Boise, ID. Wondering if there is a good rule of thumb on when to reset the altitude dial for 200 feet above airport elevation and when to start the 500 feet per min down, during the descent?

[@citationpro]

At my operation we normally set the pressurization system as part of our Top of Descent checklist. In other words, shortly before or shortly after beginning our initial descent from cruise altitude. The main thing to remember is that you don't want to "outrun" the pressurization system during descent and reach an actual altitude prior to the cabin pressure. If the cabin altitude is 4000 feet and you're descending through 4000 feet at 2000 feet/min, you're essentially an unpressurized aircraft and your ears will feel the 2000 fpm descent. You always want the cabin altitude to be lower than your actual altitude until right before landing. If the cabin is at 7000 feet cabin altitude, it will take about 14-20 minutes to "descend" the cabin to sea level, assuming a descent of 300-500 fpm. Therefore, ideally, you should set the pressurization controller at least 20 minutes before landing.

[@robinraphaelriverapomales2184]

Thanks for the great videos. You also explain and simple to understand the systems; Excellent presentation... now I know what a professional is supposed to be. Captain it will be possible that you can prepare some videos Citation 560XL will be very grateful Thank you very much in advance Robin Raphael Rivera-Pomales

[@dfort5203]

Do you know what happens when you have your gear worked on and they get the squat switch out of adjustment and you pull n2 below 85%. ? Complete de pressurization at 39,000 feet bullshit design.

[@citationpro]

@@dfort5203 that's a very interesting scenario. The cabin altitude limit valves should take over and prevent the cabin from climbing above about 14000 feet. Still, you're right, certainly not a good situation. It goes to show the importance of thorough maintenance tests before returning a plane to service. How would you design the system to prevent this from happening?