@@kamakaziozzie3038this video is very general in nature and should be treated that way. If your studying how to fix these machines, stick to the text books. There are a couple of BOEING videos out there that are excellent for system description and operation
Tassos Anastasopoulos The first time I watched a video, before I got used to his accent, I thought he was saying “As always, I will be doing absolutely fantastic.” Haha
having studied ...air conditioning I like this episode. And when I landed with my last flight weeks ago and outside looked back to the plane (or at boarding) I saw this openings for the heat exchanger and thought "what is that? that's a cool question for Mentour" but forgot it then. Shortly later, today... here we go! 👍 And thank you for the effort for all this graphics and pictures, that was a lot!
This video is a life saver! I'm gonna do my Aircraft General Knowledge ATPL exam next week and air conditioning was the one chapter i really struggled to understand. Until now. Thank you so much!
For what its worth the "dryness" at altitude is due to the _very_ low dew point of the air at 30,000 ft. Something like -40 degrees or so. If you take a wet napkin and hold it over the air vent at altitude, it will freeze quite rapidly since the air is so dry. The water separator in the air cycle machine is really only needed when you're closer to the ground and the dew point is high enough to condense inside the expansion section.
One interesting fact about pressurisation that I read about is that this process of pressurising and de pressurising the aircraft is what makes most of the structural stress on the aircraft, so a plane that flies many short flights per day will get much more wear and tear than a plane flying long haul flights with more hours but only one pre/de pressurisation processes
Went on a plane for first time and because of you and your videos I felt better about going. Thanks for being the awesome pilot you are and making these videos:) Thank you
Just a clarification on the working of the packs.. The air cycle machine that cools the bleed air consists of a compressor and turbine. After a first heat exchanger, the air goes through the compressor so the temperature is raised before going through a second heat exchanger. This makes this heat exchanger more efficient because there is a higher temperature difference. Then it goes through the turbine to cool it back down, run the compressor and a fan that draws outside air over the heat exchangers because when it is sitting at the gate they need air flow as well. At this point the temperature can be below freezing so some bleed air can be routed to bypass the air cycle machine to keep it above freezing and keep any water in the air from icing up the system. This cold air is kept at a stable temperature that way and the system regulates cabin temperature by allowing more or less uncooled bleed air to mix with the cold air.
It is little known that pilots need to have a top-notch olfactory sensory system. It's one of the first things you learn in aviation school, just like sommeliers who are trained to smell cork taint in wines. You have to smell different burned things and identify which one is the burnt bird. Failure to identify which smell is the burnt bird results in immediate expulsion.
Love the videos, but two questions on this one Mentour: 1. Why is the water removed from the air intentionally when this is a common complaint on aircraft. Why not keep a comfortable level (or at least more comfortable) level of humidity in the air by removing less water or none at all? 2. How can you smell a bird burning after a bird strike if the burn chamber is after the bleed chamber. If you're not smelling burning jet fuel usually why would you smell burning bird?
At altitude there is very little moisture up there, also dry air is good for preventing corrosion on the air frame, Bleed air is compressed air about 250C degrees at about 40 psi, when u compress air it heats up at that temp. U will easily roast that bird to bits
I’m glad newer aircrafts are getting away from bleed air system, it is too dry and easily prone to fume events which can be lethal in the long term especially for pilots and flight crew
The newer aircraft still have the same fundamental problem... outside air is super old and therefore carries very little moisture. When that air is subsequently warmed up the relative humidity is even lower. Doesn’t matter how the air got pressurized, it’s the source. Adding humidity would be possible by humidifier, but impractical weight to carry.
You mentioned several times that the engines need bleed air to start the engines. I'd love to see a video about why that is, plus any other technical information about how jet engines work. I know there are several videos out there that dryly explain it, but it's just so easy to understand things the way you explain them. Thanks for the great video.
@@WELLINGTON20 not about to review this entire episode, but Mentour has explained it thoroughly. Hence my comment. You definitely must have missed it. Remember, you really must light the charcoal first if you are going to roast anything.
Some times your aircraft is sucking in exhaust from another aircraft in front of you. If the wind is just right, this may happen. Peter mentioned the packs (air cycle machines) keep the cabin pressurized but needed to mention that the outflow valve(s) in the rear bulkhead really control the pressurization. The functioning of the air cycle machine is a study in thermodynamics. It is a complete course by it's self. I never completely understood it.
You make some good points. This video is a very basic overview of not only the pneumatic system but also the air conditioning and pressurisation systems. The air cycle machine is a very interesting device, as is the rest of the pack
Not a bad video but I would like to clarify a few things, @2:13 that is not a B737. Apart from the engine and strut being wrong, the airstart truck would be parked on the right hand side of the aircraft because that is the side with the pneumatic ground air connection so #1 engine can be started first @2:53 nice animation - has a few problems, but that is not a B737 engine @4:45 “the packs are basically controlling the pressurisation” - the air conditioning packs force the air into the airplane pressure vessel and the cabin pressurisation system controls the rate that the air flows out of the cabin @5:38 that is a very simplified diagram of the pack @9:11 I think you will find that during flight the air from the equipment cooling system is used to heat up the sidewalls of the forward cargo compartment. Recirculation fans pull air in from the passenger cabin and supply it to the main distribution manifold. The right recirculation fan pulls in air from the collector shroud in the forward cargo compartment. Floor grills in the passenger compartment (at the bottom of the cabin side wall panels) permit airflow into the collector shroud. The left recirculation fan pulls in air from the distribution compartment. @9:50 my understanding of the recirculation system is that it supplies air for ventilation which decreases the use of air from the engine bleed system and therefore saves on fuel, ie: decreases fuel consumption. It’s not to reduce the strain on the packs, that’s just a side effect @11:50 only one Cabin Pressure Controller controls the outflow valve at any time. The other Cabin Pressure Controller is a backup. The active controller changes for every flight or when there is an autofail event. @12:31 would have been nice if you had explained about the pressure bump. During the takeoff phase, the system pressurises the cabin to 0.1 psid below field elevation. This prevents the uncomfortable pressure bump (momentary pressure increase) at airplane rotation. @17:17 CH 36 pneumatics probably has more defects than any other system on the aircraft
What you were saying about being able to identify which engine was affected by bird strike depending upon where the smell was. Well, I'm reminded of the Kegworth air crash in 1989. The captain having been used to a previous model of 737 assumed that the problem was in the right-hand engine due to the smell in the cabin. In fact the left-hand engine had thrown a blade. I'd guess that there is better training now when pilots move from one model to another. Although MCAS ...
Many years ago, I flew from San Francisco to Honolulu in an OLD L1011. We could smell kerosene in the cabin for the entire flight. There were no mishaps, but I wondered how well maintained the old Lockheed had been. Good video👍.
Thanks for all your videos. I'm a nervous flyer so learning more helps to make sense of everything that's going on. I think I've actually been converted to an aviation enthusiast (although the fear probably won't completely go away lol).
Thank you Mentour for the video, can you explain the effciency difference in the "old" bleed air system and the newer compressor driven air system? What level of fuel saving is between the two systems? Thank you again and have a great day.
And then, taking some air from that process, which is way to hot to pump into the cabin as heat, and cooling it down to a point where it is way to cold to use as AC. AND THEN adding more hot air to it to make it the right temperature.
10:55: I remember back in the 70s riding with my brother in his Datsun 510 sedan trying to get up to Paradise on Mount Rainier. That poor car was gasping half way up the ascent, lol!
Cap Eddy Rickenbacker use to have to come down from high altitude ( for his aircraft ) to try to warm up. Your cabin heater was a silk scarf, leather helmet and googles, flying togs. Open cockpit and engine noise and fumes at practically arms length. Those pioneer air men were as supermen with an incredible indomitable spirit. Medal of Honor and many conspicuous outstanding Valor Awards. 🇨🇭🇺🇸🇨🇭
Hi mentour, can you please do a video comparing the A220 family and the 737 family and what impact the success of the A220 have on the 737 especially the smaller variants of the 737.
If there’s only one source to prep for the cadet pilot interviews I would choose mentourpilot… Thank you so much Petter, you helped me immensely in the interviews
The physics behind the operation of an air cycle machine (pack) are fascinating. Hot bleed air in...cool/cold air out. And all done without a refrigerant! Very clever manipulation of pressure and temperature with some heat exchangers along the way. Interesting piece...Cheers 👍
Just a bit more specific, Air cycle machine is one system inside the PACK. PACK(Pressurisation Air Conditioning Kit) is also responsible to recycle the stale air in a regulated airflow to maintain Pressurisation
@@rishavnandi6697I never knew what the acronym PACK stood for 😅 You are correct that the ACM is just one part of the PACK system. However, l’m not sure what you mean by it’s responsible to recycle the stale air?
Back in the 70's/80's it was popular to hand out candies during descent to help with ears popping. Question: Was air pressure manually controlled in those days? There seemed to be more abrupt changes in cabin air pressure. I don't even notice my ears popping in modern a/c. BTW, always great videos and massive amounts of interesting info.
I think it's a newer control system that takes external air pressure into account, instead of just having an extremely basic reactive control system for the outflow valve. It seems to me the older the plane the more abrupt the changes are as well. The automatic controls he describes follow a system of proportional ascent and descent when climbing and descending, whereas back then, they simply maintained a certain cabin altitude, descending rapidly with the descent once below 8000 ft, and ascending rapidly until 8000ft before it suddenly stops ascending.
Two questions: 1. Can planes communicate with ATC via the flight computer (and vice versa) or only via audio? 2. Why don’t airplanes have 3-point seatbelts?
What happens when the seal on the turbine shaft starts failing? Does everyone breath in atomized turbine oil? Is there a way to monitor air quality on board?
That's possible with older engine types, like JT8 D for example. Newer engines, like cfm56 in 737s were designed with bearing sumps sealed with multiple labyrinth seals, pressurized with air to keep lubricating oil inside. If any leak occurs, it will be drained from the sump overboard. Maint crew will notice increased oil consumption, nothing more.
It smells of old socks. If it occers the crew will shut off the bleed on the affected engine. They will then open the crossfeed valve and feed the packs from the other engine. But, yes, it is rare as the air in the compressor section is at a higher pressure than the bearing housings so tends to leak into the housing pushing any oil inwards.
35 Years ago, our Thermodynamics Professor shows us, that a jet-engine breathe the air of a tennis court per second (6 to 700 kg/m³)! Nower days it's up to 1,2 tonns of air per second... Thank you, for that very infiormative channel! Greetings from Germany !
Interesting video. Regarding smoking, I flew on props and jets in the '50s and '60s and don't recall being overwhelmed by smoke - the cabin seemed to clear pretty quickly and most smokers were in a lounge area. There were ashtrays in the arm rests even back on the DC6s I flew on but I rarely noticed anyone smoking near me. Not sure if the DC8 or 707 used bleed air for pressurization but believe they took in a bit more outside air as did the DC9. Aside from that, the number of 'fume' events related to the bleed air seals seems to be increasing - for some reason affecting certain airlines more than others.
Pressurized piston-engine planes usually get air from their turbochargers. I was just looking at a Cessna P210T that was in the shop who look after my plane. Nice plane, but the bill for the spar inspection was several times what my much-more-modest plane is worth.
@Mentour Pilot: Often when I'm sitting in last rows of a plane, I can smell burnt fuel when engines are started. When I get places in the front I never have that sensation. Could you tell me why this could happen? If feel that it is connected with the things you discussed in this video. Thanks!
Hi Mentour, nice video ! Quick question: Would it be possible to re-moisture the cabin air ? Waking up during a long flight with your eyes, tongue and al completely dry is the worst feeling. thanks
@mentour. Thank you so much!! I don't know if you saw that I texted you on your app's forum (and on few other videos) to make a please make a video like this one, I super appreciate you releasing it this week ! 🙂🙂🙂🙂 Your the best! .
Very good. I think it would be interesting to cover the British Midland Flight 92 accident, wich is related with wrong assumptions about the bleeded air source.
I commend Boeing for its bleedless, all electric pressurization in the B787. If the bearing seals of the engines fail smoke from the engines enters the cabin. It’s carcinogenic and a neurotoxin. Happens a lot.
10:20 It's very noticeable for me when I had sinus infection, while other can equalize pressure differential in their ear without any thought, I had deliberately force myself to yawn. The landing part is the most painful part, I have to see barometer on my phone to see how much more suffering left I have to endure. at least when I see the barometric altitude at negative on final, I know it was the peak of the pain and once we've landed and the engine has spooled down the pain would be gone. 8000 ft is painful, idk about 40K feet, people who have sinus infection and severe cold would have probably lose their hearing.
You perfectly describe why flight is so miserable for me... I am sensitive enough that I develop problems as low as 5,000 feet- when visiting family in the West I had to have my wife drive because crossing the Rockies was hell. So for me, cruising at an effective 8,000 feet is physically debilitating for hours at a time.
Most commercial jets use the same idea of ‘bleeding’ hot compressed air from inside the jet engines and then passing it through a set of machines to be processed and finally piped into the passenger cabin. As a plane flies, fast-moving air enters both the jet turbine engines. This fast-moving air is compressed as it passes through layers of fan blades inside the turbine. It’s at the compressor stage that a portion of the hot air is ‘bled off’ from within the turbine. The air generated at this point is therefore known as bleed air. Now, this bleed air is very hot, with a temperature in the range of a couple hundred degrees Celsius so it obviously must be cooled first. That’s why this hot bleed air is allowed to expand and passed through a heat exchanger so that it cools to a comfortable temperature. This cool, filtered air is then dispersed in the passenger cabin at a pressure that humans can comfortably breathe.
Air is bleed off from the compressor, not the turbine. The only filtered air is the recirculated air. There are a couple of stages of heat exchanger, but the ACM does most of the work to cool the air
Hello Petter, why, during the startup of the engines (or at the beginning of the taxi phase) often a strong smell of jet fuel invades the cabin? Is this caused by the bleeding? Isn't the fuel injected valley of the compressor?
On low power settings while standing still jet engines tend to recirulate air. Meaning the air is pushed out at the back and some of that air is sucked back in at the front. Combined with some incomplete combustion during startup, you might smell jet fuel.
I flew to cusco once where the landing altitude is over 10,000 feet with terrain all around. It did make me wonder how the pressurise manages during the descent and climb at just 2,000 feet above the cabin altitude. Especially since on takeoff it would reach 14,000 feet in under 2 minutes where oxygen masks would be deployed. So I was wondering how quickly the engines are able to build up enough bleed duct pressure whilst already under a lot of demand on takeoff due to the thin air and terrain around the airport and possibility of needing engine/wing anti ice.
Cabin Altitude is maintained to the landing strip altitude. So if u land atn airport 12000 feet AMSL, cabin altitude from the start is set at 12k and not 8k. This is done to climatize human body and prevention negative air pressure inside the cabin. Lastly there isban outflow flow valve that releases cabin pressure into the atmosphere. Depressurization happen very quick became air just wants to rush out at the slightest opening of the outflow valve
Actually I see it as a common airplane because @Mentor wants to unite aviation. You can notice that he more often talks about other airplanes, not only his favorite 737.
Petra, I recently watched a 60 Mins segment in which they discussed this very topic of the bleed air system. In this interview they talked with several pilots who are suffering from various illnesses that they claim are in direct connection to breathing this engine bleed air. From watching this I got the impression that this air is not tested and the filtration process is not nearly as effective as the airlines and manufacturers claim. Do you have any input? Have you seen this program? I am quite concerned about breathing this air and more importantly concerned for the flight crews.
I have the feeling, that at this topic there is a lot of missunderstanding. My perception is the following: The air does not get polluted by the system directly, by the construction or the components themselves. The problem is the air all around the aircraft while standing at the gate: When it's standing there and the APU (Auxiliary power unit) at the tail is running it creates such a polluted air and when then the wind carries this directly into the cabin via open doors or the starting air conditioning then we get the very bad air inside, the same when the main engines starts and the plane is still standing, and the engines are running slowly and therefore the exhaust gases aren't yet blown so strong away but get blown by the wind (if it comes from behind) directly to the entrance of the engines where this exhaust gases are sucked in again and goes then in parts into the cabine... so it's just the bad exhaust air around the engines that gets sucked in again or simply comes in by the open doors, but it's not the construction itself getting the air from the engines compressors. I saw all this very often, when I was flying, even the last time: I had to enter the plane at the rear door, people jamming, I had to stop 1 step outside the rear door, the APU was running and strong wind blew the exhaust fume directly into my face (and into the open door into the cabin), I had to stop breathing, had the feeling breathing in directly the exhaust fume would be very bad, hardly couldn't breath. The bad thing: before me was a father with a baby. I had this once even more extrem because it was very stormy and both doors were open at boarding and the very strong wind somehow very directly brought all the exhaust fume from the APU into the cabin and the bad air was getting worse and worse inside and (I am also a bit sensitive) had the feeling I hardly couldn't breath anymore properly and bording went so slowly, so it was for long, and I thought why the hell don't you close one door, the rear door near the APU that the wind can't push in the air. That I might be right with my theory could be maybe proofed because all this bad air situations always stop after a couple of minutes after we are in the air, so then the wind can't push bad exhaust fume anymore through the doors or towards the entrance from the engines. For me it's a tragedy for the crews, that have to breath in every day this dirt. Why can't they start the APU later or at least leave the rear door closed when the wind is coming from behind, why not placing the plane always in that direction into the wind (at "open field standing places") that the wind is not coming from behind, is the health of people not worth this bit of complications that would come along with this methods? Would like very much to know form @Mentour Pilot if my technical suggestion is right.
@@MentourPilot Great. I look forward to that video. I am a Patreon customer of yours and support your channel. I find it easier to communicate with you on RUclips as opposed to the app simply because my phone is old and doesnt support your app to well. None the less...thank you for all that you are doing for aviation.
I knew that. When I first began flying I could always detect a very faint odor of jet exhaust. It was later on that i found out that the air we breathe is indeed bled off from the engine and it acquires that very faint odor.
If takeoff and landing altitudes are both above 3km(~9300ft) (like in La Paz, Bolivia), there is a different pressurisation schedule: you keep the initial takeoff pressure until landing starts.
The 787 approach is better. When you make pressurization and climate control independent of bleed air from the engines, you can also do a better job of controlling the temperature and humidity.
You were talking in this video how you can detect which engine is hit by a bird by where the smell comes into the hull the first. But there are several crashes happened where the pilot shuts down the wrong engine. Also because they cannot see the engines from the cockpit. What i was always wondering is why there are no camera's pointed to critical aircraft parts like the wing edges, landing gear, engines and rudder. In case of a problem the cockpit crew can put the image on one of the screens?
@@stewiegriffin9218 A Goprto type of cam in a shatterproof glass enclosure is likely not a big deal. To retrofit, yes. To implement in the design phase, no.
Some asian airliners already have external cameras so passengers can see above/under the plane. This makes sense to have cameras pointing at the wings/engines
Or the crew can just look out a window. If there's something abnormal, there's generally passengers that are also keen enough to alert the crew. But often with bird strikes, it's not visibly apparent which engine was stuck. So a camera isn't necessarily helpful anyhow.
One day I flew in an unpressurised airplane (Beech 99) at 18, 000 ft. The bag of chips was really balooned up. Also we had oxygen with us. :) Also, some aircraft like the Emb-120, C-17, C-5 use Oxygen tanks and not generators.
The Cabin pressurized with exhaust gasses for the flight duration can not be a good thing , Can't be nice for the Pilots and Cabin Crews knowing that their work place is heated with exhaust fumes from the jet engines,or the Ground Crews breathing exhaust gasses for a good percentage of their shift , The upside the pay is good !
@@markf5437 I believe the bleed air is extracted from the engine before the burn chamber. You are just breathing the air that enters the turbofan but compressed, heated, and cooled.
@@tonyperez8683 It is air that has been through internals of a mechanical compression process of shafts turbines bearings etc operating @ +600c or above there will be fumes from the oil lubricating the bearings
I work for the company that makes the heating packs and precoolers for the Boeing 747. Im the person who has to repair them and ive had to remove many birds from the Ram Heat Exchanger, normally its only a few feathers a beak and bones that are left by the time it arrives with me to repair.
I think I just struck gold here. This is more fun and understandable than reading books.
So glad you think so! Enjoy!
Couldn’t agree more. I’m learning so much from this man.
It is enjoyable and understandable. Nice presentation!
For a jet turbine mechanic in training, you can’t beat a textbook.
Dont forget that Books possess their own value.😉
@@kamakaziozzie3038this video is very general in nature and should be treated that way. If your studying how to fix these machines, stick to the text books. There are a couple of BOEING videos out there that are excellent for system description and operation
The red and green pillows are correctly oriented port and starboard.
That was something the viewers suggested :) we were very happy when they happened.
@@andraslibal It was his own idea as well since he had thought about that before anyone mentioned it.
lol. I didn't even notice that.
So stern would be us
@@fistsofsteel5 me too :)
Every time you say "as always" in a normal sentence I hear "I hope you're doing absolutely fantastic" in my head 🤣
Tassos Anastasopoulos The first time I watched a video, before I got used to his accent, I thought he was saying “As always, I will be doing absolutely fantastic.” Haha
having studied ...air conditioning I like this episode. And when I landed with my last flight weeks ago and outside looked back to the plane (or at boarding) I saw this openings for the heat exchanger and thought "what is that? that's a cool question for Mentour" but forgot it then. Shortly later, today... here we go! 👍 And thank you for the effort for all this graphics and pictures, that was a lot!
That means RUclips learns to read your thoughts now
They need to add humidifiers
@@technophant there is not enough water on board for humidifiers but we could use water and pee from the toilet 🤔 🙄 😑
@@shijudevarajan143 google has been doing this for years
@@mattesrocketyou are suggested to drink plenty of water while flying to combat the effects of dehydration
This video is a life saver! I'm gonna do my Aircraft General Knowledge ATPL exam next week and air conditioning was the one chapter i really struggled to understand. Until now. Thank you so much!
For what its worth the "dryness" at altitude is due to the _very_ low dew point of the air at 30,000 ft. Something like -40 degrees or so. If you take a wet napkin and hold it over the air vent at altitude, it will freeze quite rapidly since the air is so dry. The water separator in the air cycle machine is really only needed when you're closer to the ground and the dew point is high enough to condense inside the expansion section.
One interesting fact about pressurisation that I read about is that this process of pressurising and de pressurising the aircraft is what makes most of the structural stress on the aircraft, so a plane that flies many short flights per day will get much more wear and tear than a plane flying long haul flights with more hours but only one pre/de pressurisation processes
Sure but the aircraft are designed with that in mind. Some B737 do 5 or more sectors a day, which equates to many flight cycles over its life time
Went on a plane for first time and because of you and your videos I felt better about going. Thanks for being the awesome pilot you are and making these videos:) Thank you
It’s very complicated; but very well explained. Thank you for taking your time putting these videos together. RgY 👍💯
Your video in 19 minutes, has more easy explanation than 1 month of class with my teacher at uni. Thanks from Brazil!!
Not air conditioning, life support. Its amazing how we trust technology to keep us alive in near space and even more amazing how rarely it fails.
Near space? Not even close
@@joet603 so where does near space start? It's a term I just made up.I can't find any reference to it. Outer space is reguarded as 100km +.
I just have to say... that is one kickass thumbnail!
1:48
"And make it possible to breed inside of the Aircraft"
😂
Mile high club here we come! 🤪
Just a clarification on the working of the packs..
The air cycle machine that cools the bleed air consists of a compressor and turbine.
After a first heat exchanger, the air goes through the compressor so the temperature is raised before going through a second heat exchanger.
This makes this heat exchanger more efficient because there is a higher temperature difference.
Then it goes through the turbine to cool it back down, run the compressor and a fan that draws outside air over the heat exchangers because when it is sitting at the gate they need air flow as well.
At this point the temperature can be below freezing so some bleed air can be routed to bypass the air cycle machine to keep it above freezing and keep any water in the air from icing up the system.
This cold air is kept at a stable temperature that way and the system regulates cabin temperature by allowing more or less uncooled bleed air to mix with the cold air.
Do you work for Honeywell, Liebherr or Secan? You must work for one of them with such a good understanding of the whole system
@@st4rskream
I'm an aviation maintenance technician (plane mechanic).
I've worked on many different planes and systems.
@@muskiet8687 Similar to me although i work only on the bleed air systems for the A320, B747, F7X and A380.
Planes are outstanding. Absolutely fantastic.
Whoever does your graphics is very good. A+
Q: How does the Boeing 737 Bleed-air system work?!
A: It bleeds air into the Boeing 737.
It is so nice to see you using footage from argentina in 2:22! SABE airport
When you say burnt bird, I think of sunday lunch and the chicken in the oven, my missus is usually quite good at setting the oven timing
I don't know why I find "the smell of burnt bird" so funny. :D
It is little known that pilots need to have a top-notch olfactory sensory system. It's one of the first things you learn in aviation school, just like sommeliers who are trained to smell cork taint in wines. You have to smell different burned things and identify which one is the burnt bird. Failure to identify which smell is the burnt bird results in immediate expulsion.
You mean it startles your appetite?!
@@yatorke1761 Well... No. 😁
Love the videos, but two questions on this one Mentour:
1. Why is the water removed from the air intentionally when this is a common complaint on aircraft. Why not keep a comfortable level (or at least more comfortable) level of humidity in the air by removing less water or none at all?
2. How can you smell a bird burning after a bird strike if the burn chamber is after the bleed chamber. If you're not smelling burning jet fuel usually why would you smell burning bird?
Clinton Mead Water is only removed on departure from humid tropical airports.
At altitude there is very little moisture up there, also dry air is good for preventing corrosion on the air frame,
Bleed air is compressed air about 250C degrees at about 40 psi, when u compress air it heats up at that temp. U will easily roast that bird to bits
@@gordonrichardson2972how does the water separator know what airport you are at?
I’m glad newer aircrafts are getting away from bleed air system, it is too dry and easily prone to fume events which can be lethal in the long term especially for pilots and flight crew
@Minella Mita How tough would it be to toss a few gallons of distilled water into the cabin?
@@davidwhite2011 I'd imagine they'd have enough water to humidify the air for the entirety of a flight.
The newer aircraft still have the same fundamental problem... outside air is super old and therefore carries very little moisture. When that air is subsequently warmed up the relative humidity is even lower. Doesn’t matter how the air got pressurized, it’s the source. Adding humidity would be possible by humidifier, but impractical weight to carry.
You mentioned several times that the engines need bleed air to start the engines. I'd love to see a video about why that is, plus any other technical information about how jet engines work. I know there are several videos out there that dryly explain it, but it's just so easy to understand things the way you explain them. Thanks for the great video.
Love your Port and Starboard pillows!
Your illustrations are always top notch and help your narrative immensely. Way to go!
Ahh! This explains the KFC smell in the cabin whenever engines swallow a bird.
It doesn’t explain it though you’ve just roasted yourself and you don’t know it
@@WELLINGTON20 not about to review this entire episode, but Mentour has explained it thoroughly. Hence my comment. You definitely must have missed it. Remember, you really must light the charcoal first if you are going to roast anything.
@@WELLINGTON20 it does - mentour himself literally said this is why you get a KFC smell (in another video)
Some times your aircraft is sucking in exhaust from another aircraft in front of you. If the wind is just right, this may happen.
Peter mentioned the packs (air cycle machines) keep the cabin pressurized but needed to mention that the outflow valve(s) in the rear bulkhead really control the pressurization.
The functioning of the air cycle machine is a study in thermodynamics. It is a complete course by it's self. I never completely understood it.
You make some good points. This video is a very basic overview of not only the pneumatic system but also the air conditioning and pressurisation systems. The air cycle machine is a very interesting device, as is the rest of the pack
2 days ago I ended up in that 737-900ER windowless 'window' seat. Thanks for letting me know why it exists
I have the pleasure of repairing parts of the bleed air systems, great to see how you use it. 👍
We used to call the ground ASUs (Air Start Units) "Huffers".
Not a bad video but I would like to clarify a few things,
@2:13 that is not a B737. Apart from the engine and strut being wrong, the airstart truck would be parked on the right hand side of the aircraft because that is the side with the pneumatic ground air connection so #1 engine can be started first
@2:53 nice animation - has a few problems, but that is not a B737 engine
@4:45 “the packs are basically controlling the pressurisation” - the air conditioning packs force the air into the airplane pressure vessel and the cabin pressurisation system controls the rate that the air flows out of the cabin
@5:38 that is a very simplified diagram of the pack
@9:11 I think you will find that during flight the air from the equipment cooling system is used to heat up the sidewalls of the forward cargo compartment. Recirculation fans pull air in from the passenger cabin and supply it to the main distribution manifold. The right recirculation fan pulls in air from the collector shroud in the forward cargo compartment. Floor grills in the passenger compartment (at the bottom of the cabin side wall panels) permit airflow into the collector shroud. The left recirculation fan pulls in air from the distribution compartment.
@9:50 my understanding of the recirculation system is that it supplies air for ventilation which decreases the use of air from the engine bleed system and therefore saves on fuel, ie: decreases fuel consumption. It’s not to reduce the strain on the packs, that’s just a side effect
@11:50 only one Cabin Pressure Controller controls the outflow valve at any time. The other Cabin Pressure Controller is a backup. The active controller changes for every flight or when there is an autofail event.
@12:31 would have been nice if you had explained about the pressure bump. During the takeoff phase, the system pressurises the cabin to 0.1 psid below field elevation. This prevents the uncomfortable pressure bump (momentary pressure increase) at airplane rotation.
@17:17 CH 36 pneumatics probably has more defects than any other system on the aircraft
What you were saying about being able to identify which engine was affected by bird strike depending upon where the smell was. Well, I'm reminded of the Kegworth air crash in 1989. The captain having been used to a previous model of 737 assumed that the problem was in the right-hand engine due to the smell in the cabin. In fact the left-hand engine had thrown a blade. I'd guess that there is better training now when pilots move from one model to another. Although MCAS ...
It was a shame the captain got the blame for that, rather than the useless instrumentation.
Many years ago, I flew from San Francisco to Honolulu in an OLD L1011. We could smell kerosene in the cabin for the entire flight. There were no mishaps, but I wondered how well maintained the old Lockheed had been. Good video👍.
THANKS VERY MUCH FOR ALL THE INFO!
you have no idea how much this helped me, I'm going up for easa module 7 exam next month and this helped me a lot, thanks!
Thanks for all your videos. I'm a nervous flyer so learning more helps to make sense of everything that's going on. I think I've actually been converted to an aviation enthusiast (although the fear probably won't completely go away lol).
Great video. Very insightful. Really appreciated the animations as well. 👏
Thank you Mentour for the video, can you explain the effciency difference in the "old" bleed air system and the newer compressor driven air system? What level of fuel saving is between the two systems?
Thank you again and have a great day.
Great video, I love the technical ones where you explain the details to the questions that come to mind when I fly in a 737
Ahh, air starters. Using a turbine to spin another turbine which starts the actual engine turbine. I love aviation.
[img]Xzibit picture[/img]
And then using the other engine to build up bleed duct pressure to cross start the other engine.
AND THEN using engine motive flow fuel pressure to move fuel from the tanks to the engines without needing to use the fuel boost pumps
And then using said bleed air to keep us all alive at 35,000 feet.
And then, taking some air from that process, which is way to hot to pump into the cabin as heat, and cooling it down to a point where it is way to cold to use as AC. AND THEN adding more hot air to it to make it the right temperature.
We`ve missed the doggies. :)
Thank you, very instructive and the way you explained it makes it easy to understand.
10:55: I remember back in the 70s riding with my brother in his Datsun 510 sedan trying to get up to Paradise on Mount Rainier. That poor car was gasping half way up the ascent, lol!
Cap Eddy Rickenbacker use to have to come down from high altitude ( for his aircraft ) to try to warm up. Your cabin heater was a silk scarf, leather helmet and googles, flying togs.
Open cockpit and engine noise and fumes at practically arms length.
Those pioneer air men were as supermen with an incredible indomitable spirit.
Medal of Honor and many conspicuous outstanding Valor Awards. 🇨🇭🇺🇸🇨🇭
When it smells of goose it's Christmas! 😍
If it smells of goose you have lost o e engine. Lol.
Nice you were in Argentina! been following your channel for last couple weeks, excellent work Peter!
Hi mentour, can you please do a video comparing the A220 family and the 737 family and what impact the success of the A220 have on the 737 especially the smaller variants of the 737.
Great video Mentour I enjoyed watching it, have a fantastic weekend my friend.
Excellent presentation, very informative.
Glad you liked it!
Very informative, one of your best. Thank you.
If there’s only one source to prep for the cadet pilot interviews I would choose mentourpilot… Thank you so much Petter, you helped me immensely in the interviews
Mentour, you should do a video on all of the worst or out-dated systems on the 737-NG’s! Would love to know your opinion!
The physics behind the operation of an air cycle machine (pack) are fascinating. Hot bleed air in...cool/cold air out. And all done without a refrigerant! Very clever manipulation of pressure and temperature with some heat exchangers along the way. Interesting piece...Cheers 👍
Just a bit more specific, Air cycle machine is one system inside the PACK. PACK(Pressurisation Air Conditioning Kit) is also responsible to recycle the stale air in a regulated airflow to maintain Pressurisation
@@rishavnandi6697I never knew what the acronym PACK stood for 😅
You are correct that the ACM is just one part of the PACK system. However, l’m not sure what you mean by it’s responsible to recycle the stale air?
Back in the 70's/80's it was popular to hand out candies during descent to help with ears popping. Question: Was air pressure manually controlled in those days? There seemed to be more abrupt changes in cabin air pressure. I don't even notice my ears popping in modern a/c. BTW, always great videos and massive amounts of interesting info.
I think it's a newer control system that takes external air pressure into account, instead of just having an extremely basic reactive control system for the outflow valve. It seems to me the older the plane the more abrupt the changes are as well. The automatic controls he describes follow a system of proportional ascent and descent when climbing and descending, whereas back then, they simply maintained a certain cabin altitude, descending rapidly with the descent once below 8000 ft, and ascending rapidly until 8000ft before it suddenly stops ascending.
I don't care about my own discomfort just anything to stop the babies crying.
737s and a319 320 seem pretty good. The old dc9 used to always cause me ear discomfort. Those are old planes so that's maybe why
Two questions: 1. Can planes communicate with ATC via the flight computer (and vice versa) or only via audio? 2. Why don’t airplanes have 3-point seatbelts?
What happens when the seal on the turbine shaft starts failing? Does everyone breath in atomized turbine oil? Is there a way to monitor air quality on board?
Yes. No.
That's possible with older engine types, like JT8 D for example.
Newer engines, like cfm56 in 737s were designed with bearing sumps sealed with multiple labyrinth seals, pressurized with air to keep lubricating oil inside. If any leak occurs, it will be drained from the sump overboard. Maint crew will notice increased oil consumption, nothing more.
It smells of old socks. If it occers the crew will shut off the bleed on the affected engine. They will then open the crossfeed valve and feed the packs from the other engine. But, yes, it is rare as the air in the compressor section is at a higher pressure than the bearing housings so tends to leak into the housing pushing any oil inwards.
@@bobrice3957cross feed is for fuel. Cross bleed is for air
You are such a gem. Love your dog.
35 Years ago, our Thermodynamics Professor shows us, that a jet-engine breathe the air of a tennis court per second (6 to 700 kg/m³)! Nower days it's up to 1,2 tonns of air per second...
Thank you, for that very infiormative channel! Greetings from Germany !
Americans will use anything but the metric system.
Interesting video. Regarding smoking, I flew on props and jets in the '50s and '60s and don't recall being overwhelmed by smoke - the cabin seemed to clear pretty quickly and most smokers were in a lounge area. There were ashtrays in the arm rests even back on the DC6s I flew on but I rarely noticed anyone smoking near me. Not sure if the DC8 or 707 used bleed air for pressurization but believe they took in a bit more outside air as did the DC9. Aside from that, the number of 'fume' events related to the bleed air seals seems to be increasing - for some reason affecting certain airlines more than others.
Pressurized piston-engine planes usually get air from their turbochargers. I was just looking at a Cessna P210T that was in the shop who look after my plane. Nice plane, but the bill for the spar inspection was several times what my much-more-modest plane is worth.
Laura Halliday Interesting, I never thought about that!
The best video ever on aircraft pressurization and system knowledge ! Thank you
You are very intelligent am very proud of you Captain 😘😘😘
I just started watching this guy. He's absolutely amazing 👏
@Mentour Pilot: Often when I'm sitting in last rows of a plane, I can smell burnt fuel when engines are started. When I get places in the front I never have that sensation. Could you tell me why this could happen? If feel that it is connected with the things you discussed in this video. Thanks!
At the beginning the APU starts to assist engine start thus smell. Or do you mean after takeoff when engines are already running and airbourne?
have a good times sir
greetings from Turkey
This video will make me succesfull on my exam that is tomorrow
Hi Mentour, nice video ! Quick question: Would it be possible to re-moisture the cabin air ? Waking up during a long flight with your eyes, tongue and al completely dry is the worst feeling. thanks
@mentour.
Thank you so much!!
I don't know if you saw that I texted you on your app's forum (and on few other videos) to make a please make a video like this one, I super appreciate you releasing it this week ! 🙂🙂🙂🙂 Your the best! .
All I care about is that the damn things have no leg room..
H B Ryanair AND leg room? Not possible!
I like the fact he uses red green cushion like red green wing end strobe lights on a plane ! ✈️ ❤😂
Very good. I think it would be interesting to cover the British Midland Flight 92 accident, wich is related with wrong assumptions about the bleeded air source.
Another great video, loved the animation, Well done
I commend Boeing for its bleedless, all electric pressurization in the B787. If the bearing seals of the engines fail smoke from the engines enters the cabin. It’s carcinogenic and a neurotoxin. Happens a lot.
Excellent appreciable content on bleed air, Petter. Much appreciated!
When I flew on a 737-200 as a child, the pain in my ears was excruciating.
10:20 It's very noticeable for me when I had sinus infection, while other can equalize pressure differential in their ear without any thought, I had deliberately force myself to yawn.
The landing part is the most painful part, I have to see barometer on my phone to see how much more suffering left I have to endure. at least when I see the barometric altitude at negative on final, I know it was the peak of the pain and once we've landed and the engine has spooled down the pain would be gone.
8000 ft is painful, idk about 40K feet, people who have sinus infection and severe cold would have probably lose their hearing.
You perfectly describe why flight is so miserable for me... I am sensitive enough that I develop problems as low as 5,000 feet- when visiting family in the West I had to have my wife drive because crossing the Rockies was hell. So for me, cruising at an effective 8,000 feet is physically debilitating for hours at a time.
Most commercial jets use the same idea of ‘bleeding’ hot compressed air from inside the jet engines and then passing it through a set of machines to be processed and finally piped into the passenger cabin.
As a plane flies, fast-moving air enters both the jet turbine engines. This fast-moving air is compressed as it passes through layers of fan blades inside the turbine. It’s at the compressor stage that a portion of the hot air is ‘bled off’ from within the turbine. The air generated at this point is therefore known as bleed air. Now, this bleed air is very hot, with a temperature in the range of a couple hundred degrees Celsius so it obviously must be cooled first. That’s why this hot bleed air is allowed to expand and passed through a heat exchanger so that it cools to a comfortable temperature. This cool, filtered air is then dispersed in the passenger cabin at a pressure that humans can comfortably breathe.
Air is bleed off from the compressor, not the turbine. The only filtered air is the recirculated air. There are a couple of stages of heat exchanger, but the ACM does most of the work to cool the air
Hello Petter, why, during the startup of the engines (or at the beginning of the taxi phase) often a strong smell of jet fuel invades the cabin? Is this caused by the bleeding? Isn't the fuel injected valley of the compressor?
On low power settings while standing still jet engines tend to recirulate air. Meaning the air is pushed out at the back and some of that air is sucked back in at the front. Combined with some incomplete combustion during startup, you might smell jet fuel.
@@danielrose1392 Thanks Daniel! It makes sense!
So many times passengers pressing callbels and asking the crew why there is this smell. Sometimes they turn on bleed air too fast after startup :)
I was thinking of this same smell I experienced a while ago. Smells like burnt kerosene!
@@FRDRCE
It is burnt kerosene, that's basically what JetA fuel is.
I flew to cusco once where the landing altitude is over 10,000 feet with terrain all around. It did make me wonder how the pressurise manages during the descent and climb at just 2,000 feet above the cabin altitude. Especially since on takeoff it would reach 14,000 feet in under 2 minutes where oxygen masks would be deployed. So I was wondering how quickly the engines are able to build up enough bleed duct pressure whilst already under a lot of demand on takeoff due to the thin air and terrain around the airport and possibility of needing engine/wing anti ice.
Cabin Altitude is maintained to the landing strip altitude. So if u land atn airport 12000 feet AMSL, cabin altitude from the start is set at 12k and not 8k. This is done to climatize human body and prevention negative air pressure inside the cabin. Lastly there isban outflow flow valve that releases cabin pressure into the atmosphere. Depressurization happen very quick became air just wants to rush out at the slightest opening of the outflow valve
What if the heat exchanger and air conditioning fail? Will the hot bleed air be passed into the passenger cabin?
No hot bleed air will get into the cabin, there are shut off valves to regulate and isolate the bleed air.
@@e30mark thanks for clearing my doubt 👍
Best Aviation content on RUclips 👊
Me from a week ago: mentor ur a 737 pilot why is a 777 in ur intro
Mentor: takes away the 777 on the vertical stabilizer
Me now: it’s still a 777...
Actually I see it as a common airplane because @Mentor wants to unite aviation. You can notice that he more often talks about other airplanes, not only his favorite 737.
Very interesting video. Clear explanation of bleed air system
"It uploads air," haha!
Scary AOA on that graph lol. Interesting video thanks!
Petra, I recently watched a 60 Mins segment in which they discussed this very topic of the bleed air system. In this interview they talked with several pilots who are suffering from various illnesses that they claim are in direct connection to breathing this engine bleed air. From watching this I got the impression that this air is not tested and the filtration process is not nearly as effective as the airlines and manufacturers claim. Do you have any input? Have you seen this program? I am quite concerned about breathing this air and more importantly concerned for the flight crews.
Yes, that’s a different video
I have the feeling, that at this topic there is a lot of missunderstanding. My perception is the following: The air does not get polluted by the system directly, by the construction or the components themselves. The problem is the air all around the aircraft while standing at the gate: When it's standing there and the APU (Auxiliary power unit) at the tail is running it creates such a polluted air and when then the wind carries this directly into the cabin via open doors or the starting air conditioning then we get the very bad air inside, the same when the main engines starts and the plane is still standing, and the engines are running slowly and therefore the exhaust gases aren't yet blown so strong away but get blown by the wind (if it comes from behind) directly to the entrance of the engines where this exhaust gases are sucked in again and goes then in parts into the cabine... so it's just the bad exhaust air around the engines that gets sucked in again or simply comes in by the open doors, but it's not the construction itself getting the air from the engines compressors. I saw all this very often, when I was flying, even the last time: I had to enter the plane at the rear door, people jamming, I had to stop 1 step outside the rear door, the APU was running and strong wind blew the exhaust fume directly into my face (and into the open door into the cabin), I had to stop breathing, had the feeling breathing in directly the exhaust fume would be very bad, hardly couldn't breath. The bad thing: before me was a father with a baby. I had this once even more extrem because it was very stormy and both doors were open at boarding and the very strong wind somehow very directly brought all the exhaust fume from the APU into the cabin and the bad air was getting worse and worse inside and (I am also a bit sensitive) had the feeling I hardly couldn't breath anymore properly and bording went so slowly, so it was for long, and I thought why the hell don't you close one door, the rear door near the APU that the wind can't push in the air. That I might be right with my theory could be maybe proofed because all this bad air situations always stop after a couple of minutes after we are in the air, so then the wind can't push bad exhaust fume anymore through the doors or towards the entrance from the engines. For me it's a tragedy for the crews, that have to breath in every day this dirt. Why can't they start the APU later or at least leave the rear door closed when the wind is coming from behind, why not placing the plane always in that direction into the wind (at "open field standing places") that the wind is not coming from behind, is the health of people not worth this bit of complications that would come along with this methods? Would like very much to know form @Mentour Pilot if my technical suggestion is right.
@@MentourPilot Great. I look forward to that video. I am a Patreon customer of yours and support your channel. I find it easier to communicate with you on RUclips as opposed to the app simply because my phone is old and doesnt support your app to well. None the less...thank you for all that you are doing for aviation.
I knew that. When I first began flying I could always detect a very faint odor of jet exhaust. It was later on that i found out that the air we breathe is indeed bled off from the engine and it acquires that very faint odor.
8:23 burnt bird. Last vid that talked about Bird Strike said "smells like KFC" :-P
If takeoff and landing altitudes are both above 3km(~9300ft) (like in La Paz, Bolivia), there is a different pressurisation schedule: you keep the initial takeoff pressure until landing starts.
One plane I boarded had smelly jet fuel fumes in the cabin until they started something up.
The smell is from the Ramp
@@gnranger but from inside the cabin????
"Nice and survivable flight" :D
The 787 approach is better. When you make pressurization and climate control independent of bleed air from the engines, you can also do a better job of controlling the temperature and humidity.
Controlling the humidity requires a source of pure water. Such a system was proposed, but never implemented on the B787.
@@gordonrichardson2972as far as I am aware there are 3 humidifiers on the B787
This video is very informative and well narrated! You should really do training and instructional videos for the aviation industry! 👍
You were talking in this video how you can detect which engine is hit by a bird by where the smell comes into the hull the first. But there are several crashes happened where the pilot shuts down the wrong engine. Also because they cannot see the engines from the cockpit. What i was always wondering is why there are no camera's pointed to critical aircraft parts like the wing edges, landing gear, engines and rudder. In case of a problem the cockpit crew can put the image on one of the screens?
cameras sound impractical, also they'd need deicing and what not, so in essence u're introducing more problems than u're solving
@@stewiegriffin9218 A Goprto type of cam in a shatterproof glass enclosure is likely not a big deal. To retrofit, yes. To implement in the design phase, no.
Some asian airliners already have external cameras so passengers can see above/under the plane. This makes sense to have cameras pointing at the wings/engines
Or the crew can just look out a window. If there's something abnormal, there's generally passengers that are also keen enough to alert the crew. But often with bird strikes, it's not visibly apparent which engine was stuck. So a camera isn't necessarily helpful anyhow.
Weight and the most important maintenance cost. Flight attendants and flight engineers can perform the same function a camera can.
One day I flew in an unpressurised airplane (Beech 99) at 18, 000 ft. The bag of chips was really balooned up. Also we had oxygen with us. :) Also, some aircraft like the Emb-120, C-17, C-5 use Oxygen tanks and not generators.
We sacrifice a bit of fuel in order to keep the PAX alive.... Thank you Boeing, thank you Ryan Air!!!!
The Cabin pressurized with exhaust gasses for the flight duration can not be a good thing ,
Can't be nice for the Pilots and Cabin Crews knowing that their work place is heated with exhaust fumes from the jet engines,or the Ground Crews breathing exhaust gasses for a good percentage of their shift ,
The upside the pay is good !
@@markf5437 I believe the bleed air is extracted from the engine before the burn chamber. You are just breathing the air that enters the turbofan but compressed, heated, and cooled.
The PACS keep the PAX alive!
@@tonyperez8683 It is air that has been through internals of a mechanical compression process of shafts turbines bearings etc operating @ +600c or above there will be fumes from the oil lubricating the bearings
best quality tutorial ever. thanks
10:08 yeah thats why everyone is breathing fart at the back end of a long haul flight, first class or not😂
I work for the company that makes the heating packs and precoolers for the Boeing 747. Im the person who has to repair them and ive had to remove many birds from the Ram Heat Exchanger, normally its only a few feathers a beak and bones that are left by the time it arrives with me to repair.
Everybody repeat after me three times: BURNED BIRD, BURNED BIRD, BURNED BIRD.
Hi mentour pilot, love your videos. I hope you're doing absolutely fantastic.