How does the Boeing 737 Bleed-air system work?!

hi everybody very welcome to mentor and yet our video podcast as always I hope you're doing absolutely fantastic so did you know that when you're flying most commercial aircraft you're actually breathing air that's coming directly from the jet engine today we're gonna be talking about the air conditioning system and the bleed air system on the 737 this video is brought to you to get a bleed audible now if you're like me you love kind of sitting back relaxingg listening to a great audiobook or maybe a comedy show or a news show well in that case I highly recommend you to check out audible so if you use the link here below which is audible.com slash mentor pilot or if you're in the United States and you text the code mentor pilot to 500 500 well and you'll get 30 days of free trial with audible you'll get one free audiobook and two audible originals so check it out so if we start off with where bleed air comes from and why we have it in the first place and the fact is that an aircraft especially as old as a 737 is needs bleed air for a number of different reasons so we're using leaders to start up the engines we're using it to and the ice and de-ice the front of the engine cowling as some when the air comes into the engine and also the leading edges of the wings it is used to pressurize the water tanks so that you know you get water when you open up the taps in their toilets and also crucially it's what regulates the temperature and makes it possible to breathe inside of the aircraft when you're flying the breathe air can come from basically three different sources so either it can come from an external air source this is something we would use if the auxiliary power unit which is the second bleed air source is not working and an external air source I abused it actually this week the apu wasn't working and you'll see it as a huge kind of compressor bagging that makes a lot of noise and stands next to the aircraft and it uploads air in order for us just to start our engines so we get to our third lead air source which are the engines of the aircraft so when we are flying along we use the compressor stages of the jet engine to provide the pressurization and the air that we are breathing inside of the aircraft we use air from the fifth and the ninth stage of the compressor the way that the jet engine works prior to the burn chamber is that it will take in air from behind the fan in through several compressor stages that will compress the air in and then add fuel to that compressed air and burn it in the burn chamber okay and we take a little bit of that compressed air in order to feed these systems that I just told you about this also means that we're actually taking away a little bit of the power of the engine by doing so we're sacrificing a little bit of the fuel efficiency from the engine in order to to get me there for all of these systems and this is why if you look at more modern aircraft like the years boeing 787 dreamliner for example they have stopped doing that they're using electrically driven compressors instead and that is to get the absolute best fuel economy out of the engines but in the 60s kind of technology or 90s engine technology that we're using on the 77 800 we were still using bleed air from the engine so primarily the B there comes from the v compressor stage but we can also in case we have very low power setting on the engine bleed a bit of air from the ninth stage as well and that's the kind of supplementary bleed air source we have two different systems as always you know that by now there's always a backup system in case one would not work the other one can take upload and the way this works is that the bleeder is taken out of the engine it's done being rerouted through several kind of pressure switches and temperature switches that can stop it in case it feels an overpressure and over temperature and condition its them being routed out to the anti-icing system if it's needed and then is being brought into what we called air conditioning packs the packs are basically what's controlling the pressurization and the temperature that you're feeding inside of the aircraft and the way that this works is that this bleed air when it's coming into the pack it is very very hot you know that if you know your physics that if you compress air it becomes very hot and it's way too hot to be fed into the passenger compartment so it comes in and it goes through a heat exchanger now if you've seen the 77 when you've been boarding it you can see that just in front and below the word wings intersect with the body there are openings these are ram air openings so it like the word would suggest it takes the air that's ramming into the opening it brings that through and it uses it to cool down the bleeder so the bleeder goes through a heat exchanger that uses the ram air to to cool it down it then moves into a refrigeration unit that refrigerated is called an air cycle machine and then it goes to a water separator right that separates and takes away the moisture out of the air that's why by the way you can always feel so dry when you've been flying especially a long haul because the air is really dry then as it's gone through this process it's now very cold and depending on what temperature we want we can then add a little bit of bleed air that has been kind of rerouted post this refrigeration system and added hot air towards the last stage to to set the temperature so this looks exactly the same on the left side on the right side so the left pack uses the bleed air from the engine number one the one on the left side and the right pack uses it from the right engine and these systems then come together in what's called the mix manifold now there is what we call an elation vibe so there is possible it is possible to completely separate the systems from each other if you have a bleed air leak or for example an engine failure an onion fire on one side you can separate the systems to make sure that none of that bad bad air is rerouted into the cabin but the left pack is the pack that on the 77 supplies the air to the flight deck so from the left pack some of the air goes into the flight deck and since that's only a tiny little bit the rest of the air goes into the Mac mix manifold it's been mixed up with the the air from the right pack and then it's being fed into the cabin the cabinet is divided into two different zones the forward and the after zone and we have temperature controllers inside of the cockpit where we can set it it's a very rudimentary system picture like a Volkswagen Beetle from the from the 60s or 70s it is that system right we don't set a digital temperature we actually have a little knob that goes to higher hotter or colder you don't get me there it's probably one of the worst systems on the on the 737 but anyway um this is also why we got mention in this previous podcast if we would have a bird strike for example we can actually figure out which engine has been hit by the bird depending on where the smell comes from because if a bird has gone into the core of the engine on the left-hand side well then the smell of burnt bird will go through the bleed air system and it will end up in the cockpit first but if the smell comes out if the cabin crew starts telling us that it smelled like burnt bird in the back then we know that it's the right side because then the leader has been coming from that side you can actually make that distinction and it's it's very very clear when it happens anyway the air that comes from the mix manifold is now being pushed up into the cabin if you have had a bad luck of buying a window seat and you end up on the 737 without a window the window seat that's because you're sitting where the air is coming up and going up into the rises that's above in the roof of the cabin there's also Rises on the side of the cabin and all of that makes a nice mixture of air inside of the cabin when the cabin air has been used so when you guys have been breeding it for a while it's being sucked out from the bottom of the cabin and is being routed around the forward cargo bay and it's used there to heat up the the cargo the forward cargo bay and then it is either being exhausted that's going out to the overboard exhaust valve which is there and it's used during very low differential pressures but I get to that in a second or it is being exhausted by the big hole in the back which is the outflow valve which is the main kind of regulator we have for regulating the pressure in the cabin or a quite big bit of it is being used and being filtered first and then recirculated into the mix manifold and we recirculate reuse the air in order to take a little bit of strain off the packs because the less the packs have to work the less bleed air we have to take from the engines and the less fuel we're using so you are actually breathing a little bit of reused air inside of the the cabin but it has been properly filtrated before that happens okay right so that's how we manage the temperature but what about the pressurization why do we need to pressurize the cabin in the first place well the fact is that as humans we were not built to be you know hanging around at 40,000 feet we were built to be walking around on the surface of the earth so our lungs are built to take up oxygen the amount of oxygen we need at the pressure that is on the surface if we start climbing the pressure will gradually decrease as we get higher and at some point around 25,000 feet and above we cannot take up enough oxygen to live anymore this is called Death Zone this is what you've probably heard about when climbers reached its own in when they're climbing Mount ever this is where the need to start using oxygen or be very very well-prepared otherwise it will not be able to do it we climb well above that so our cruising altitude can be anything from 35 to 41,000 feet and up there in order for you to be able to breed the prep the cabin need to be pressurized or you need to breathe pure oxygen but you don't really want to sit with an oxygen mask on you would have want to be able to eat your snacks and have your drinks and talk to the people that you're traveling with so we pressurize the cabin we do in so by feeding from the air conditioning packs in enough air to keep the pressure similar to what's on the surface but it's not going to be exactly like this in the surface and I'll get to that soon so the outflow valve in the back is being controlled by two automatic pressurization controllers that make sure that the pressurization is kept within limits and it drives from open to decrease the decrease the pressure to close to increase the pressure on board and the way that we pressurize it and this is fascinating is that we will set takeoff trust and when we set take-off trust the outflow valve will drive to close and when it comes to closed we will start to pressurize the cabin so this means that the cabin altitude as in the altitude that is in the cabin will actually decrease a little bit initially and this is to make the transition from unpressurized to pressurize flight feel less for you you will feel it less by doing it this way so you start slightly pressurized we take off and as we start climbing the cabin altitude will be climbing as well at a rate that is proportional to the rate that we're climbing with the aircraft so if we're climbing with 3,000 feet per minute the cabin will be climbing or about 500 feet per minute or so when we're leveling off the cabin levels off as well and when we reach our cruising altitude of about say 40 41,000 feet the cabin will level off at a maximum altitude of 8,000 feet so you're actually sitting at about 8,000 feet altitude when you're up at the cruising level and this is why you feel sometimes you might have problems with your ears problems with sinuses and if you have a like a bag of chips or something with you you'll see that it's about to pop when you're at the cruising level and that is because you are actually at a fairly high level we will maintain that right if we do a slight climb the cabin will climb as well but not above approximately 8,000 feet and then as we start descending when we descend more than about 0.25 psi or pressure then the automatic controller will feel that we're in a descent mode and it will start to gradually descend the cabin as well so it will follow once again a proportional rate of descent down to when we get on to approach it will then continue to pressurize the aircraft so that we land once again with the aircraft slightly pressurized and that is to make sure that we don't get that kind of sudden poke sudden like clicking your ears as we touch down so once again you're gonna be landing slightly lower and slightly lower cabin altitude then what the aircraft actually is at and as we taxi in the the automatic controllers will gradually open the alpha verb to make sure that the aircraft is completely depressurized during the taxi in phase so that we are able to open the doors if we wouldn't if that didn't happen and the aircraft wasn't depressurize we wouldn't be able to open the doors and that would be a problem so the pressurization system like I said has two different automatic controllers they alternate between each flight so one on one flight second one down on the next flight and if one failed the other one automatically takes over if both of them fails well then we have a manual mode as well so we the pilots can manually manage the preservation of the aircraft but a problem that we have with this system is that if something happens for example to the outflow valve well then the aircraft might suddenly and abruptly depressurize itself and you've probably seen that in newspaper articles esta T cab the aircraft suddenly fell from 30,000 feet and the masks dropped and it was chaos in the cabin now the reason for that is what I just told you we need to have a certain pressure for us to be able to breed and if the preservation suddenly drops be it by a problem with the outflow valve or a structural problem of the aircraft well in that case we need to quickly get down to an altitude where you guys can breathe now the oxygen masks are dropped down they will give you enough oxygen to survive during the emergency descent there's about 13 minutes of oxygen that can be produced by the oxygen generators that are you know providing the oxygen they're not actually oxygen bottles they are chemical reactions that gives you the oxygen this is also why you might smell a faint burning smell if this happens because the oxygen generators actually get quite hot when they're generating the oxygen but if you are interested in knowing what we do you know when when the passengers are feeling that falling feeling and that chaotic feeling if you want to see what that actually looks like from the cockpit then I've done a video about a rapid depressurization and emerges this and how that looks in the cockpit so you can click the link here or check out the link in the description of the video now what I would suggest if you are looking at that video is to put the subtitles on because it can be a little bit hard to hear what we're saying through the the oxygen mask but it's fascinating and I highly recommend it but in essence guys this is why we have a bleed air system on the 737 we need it in order for you guys to have a nice and survivable right we need it in order to start the engines in the first place we need to de-ice the wings and the engines and the system is actually very very good and very reliable guys if you have more questions about the pressurization system maybe you want something further clarified well then put your comments in here or even more effective get the free mentor reaction app I will be in there just tag at mentor and I'll be answering your questions or there will be other professional pilots or pilot students or aviation enthusiasts and even pee bullhorn ervice flyers in the forums there are no stupid questions everyone a welcome it's a fully safe positive and constructive environment so go down there links to download it both for iOS and Android down here and join the community I also want to send a huge thank you to the sponsor of this episode which is audible now I spend a lot of time transitioning in between bases or flying as passive crew up to my training assignments in Stansted or in beta gamma or whatever it might be and I love hanging out listening to a great audio book now audible has an unmatched library of audio books and if you use this link here below which is audible.com slash mentor pilot or if you text you're in the US the cord mentor pilot - 500 500 well then you get 30 days of free trial with audible where you can check up all of their titles you'll get one free audiobook and two audible originals and a title that I think that you guys might enjoy is the last days of the concorde with some chat ooh check it out let me know what you think about audible and have an absolutely fantastic day wherever you are I'll see you next time bye bye right guys I really hope that you like that if you want more content like that more radiation content but then check this out I hope that you have subscribed to the channel and that you've highlighted little notification belt see you inside of the mentor every Asian up and have an absolutely fantastic day bye bye [Music] [Applause] [Music]

Channel: Mentour Pilot

Views: 242,281

Keywords: jet engine, jet engines, mentour pilot, fear of flying, how to become a pilot, how jet engine works, jet engine (invention), boeing 737 max, flight school, aviation facts, boeing 737ng, aircraft bleed air system, Boeing 737 AC, How you can breathe in aircraft, air conditioning and pressurization system in aircraft, air conditioning and pressurization of aircraft, boeing 737 max technology, mentour pilot 737 max, mentour pilot turbulence, mentour pilot simulator

Id: ulDZWJZBNQM

Length: 19min 27sec (1167 seconds)

Published: Fri Nov 15 2019