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Mephic

Cabin depressurization?

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I had my regular RyanAir EPKT-EDDL flight today and I have accidentally switched off Engine Bleeds when still on ground.

 

I took off and approximately after 30 minutes the oxygen masks for passengers went down and I needed to perform the appropriate actions together with Emergency NGX CoPilot.

 

I realized my mistake and I have switched on the bleeds during flight.

 

I would like to understand what consequences would it have in real life (apart from necessity to search for new job in Lufthansa). What would happen to passengers? Would I be able to continue flight (i did that actually) 

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Unless you as the pilot were aware of the problem and using supplemental oxygen, whatever happens to the passengers also happens to you. Without supplemental oxygen everyone on board would lose consciousness in a matter of minutes, and start to lose permanent brain function after 10 minutes or so if I recall correctly. You can look up "hypoxia" on google. There are many dangerous incidents involving hypoxia, especially with GA planes that have no pressurization system or manually controlled pressurization systems. There's interesting history on this issue with the 737 as well. You probably heard the TOCW at some point during your cruise mishap - Boeing never created an independent alarm/warning for loss of cabin pressure, they just tied it to the TOCW thinking pilots would be trained to know what a TOCW in cruise meant. On Helios flight 522, the crew wasn't trained to react to the TOCW warning going off in cruise, and pulled the circuit breaker to it, thinking it was a malfunction. They never put on oxygen masks, descended or attempted to target a pressurization issue - which are the proper steps to take with loss of cabin pressure according to Boeing's emergency checklist. Everyone on board eventually lost consciousness and the plane crashed. The FAA issued an air worthiness directive that instructed all 737 aircraft be retrofitted with an independent pressurization warning light. That requirement went into effect in 2014, after the release of the NGX, so it makes sense that the NGX being accurate for it's time wouldn't have that retrofit. Perhaps in a future update.

 

There's an Air Crash Investigation episode on Helios 522: 

You can also search YouTube for "hypoxia ATC" and find many examples of pilots who become incapacitated or incoherent after climbing to too high an altitude or losing pressurization. It's a very dangerous phenomenon. Our bodies are not built to handle the environment at high flight levels, and when the miracles of science and engineering that make such things possible are taken for granted horrible events can ensue. 
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Hi! Thanks for this complete answer and analysis and also for example from real world. It's really amazing how PMDG depicted the 737 and it's quirks. Although one thing does not match: There was never any alarm going off - only the master caution button went on together with pass oxy. I was surprised there is no sound alarm unless my FO switched it off before I could hear it which would be weird.

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I follow RYR SOPs (not fs2crew to mention) and they have a solid safe guard in place to check this panel. On the ground and part of the before takeoff checklist they perform a captains review of PACKS, BLEEDS, SPEEDS. So if this has been missed it will be picked up. Also you re-check it during the after takeoff checklist - “AIR COND and PRESS...SET” read ALOUD by PM. You then check the pressurization panel again at ten checks or 10000ft and every 10000ft after that.

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I will add this to my checklist. I don't have fs2crew reboot maybe it's there in one of the sops already but I have no money currently to invest in fsx ;)

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Well i got a copy of the SOPs from a friend its not from Fs2crew. Are you not using FSX?

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What i meant is to invests more money in FSX addons ;) Besides I'm not sure if FS2Crew Reboot is really worth the investment and why. I read through the flows and apparently the older version fits my needs, but let's see.

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Unless I drastically misunderstand European airlines, I'm not thinking a RyanAir reject has a prayer of finding employment at Lufthansa. ;-)

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Hi! Thanks for this complete answer and analysis and also for example from real world. It's really amazing how PMDG depicted the 737 and it's quirks. Although one thing does not match: There was never any alarm going off - only the master caution button went on together with pass oxy. I was surprised there is no sound alarm unless my FO switched it off before I could hear it which would be weird.

 

No problem. Yes, I agree it’s amazing how they modeled every little quirk. If you haven’t done so already, read the “details and quirks” section at the end of the introduction manual. Remarkable how much effort they put in to make the NGX as accurate as it is. 
 
Not sure what happened with the aural warning, but I tested this on my system and the NGX responds accurately. If you do not put packs or bleeds on, the TOCW goes off at about 10,000ft*. Shortly after the Master Caution and overhead warning light come on, along with the associated passenger oxygen light on the overhead. It all works as it should for me. 
 
*Edit: I should clarify that I meant the TOCW goes off at about 10,000ft cabin altitude. The plane itself should be at or close to cruise altitude when this happens. Normal cabin altitude for a 737 in cruise is about 8,000ft.  

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