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

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

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 :)

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

That means RU-vid 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

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

Mile high club here we come! 🤪

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. 😁

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)

Glad you liked it!

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 +.

It was a shame the captain got the blame for that, rather than the useless instrumentation.

The dry air problem is hard to solve because cruising altitude is so cold that there's very little water vapor in the outside air. Newer designs try to recover and recycle water vapor from the exhaust air. Or you can recycle more air, but that also retains carbon dioxide. (Not enough to be dangerous, but too much recycling is bad for cabin comfort.)

@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.

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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.

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

If it smells of goose you have lost o e engine. Lol.

Laura Halliday Interesting, I never thought about that!

Americans will use anything but the metric system.

H B Ryanair AND leg room? Not possible!

It becomes a bit more complicated but essentially the same principle

At the world's highest airport (16,000', in China), I heard that pilots need to press a special button in the cockpit to stop the oxygen masks from deploying when the plane has reached it's gate & airport staff open the aircraft's doors (since at that altitude the atmospheric pressure is so low, the aircraft would otherwise think it had depressurised)

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.

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?

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

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.

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 👍

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.

It's the other way around in helicopters, though. I've always wondered why that is.

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 RU-vid 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.

The smell is from the Ramp

@@gnranger but from inside the cabin????

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.

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

Lancashirelad ty:)

doesn't matter as your plane falls out of the sky and you die. :) As mentioned the APU, he mentioned it at the start of the video, but didn't really go into it.

Bad day

Brofights sorry to hear that man

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