44

What happens during a flight cycle is the humidity is high during departure, from ambient air and the moisture from the pax, but over time the air dries out because the bleed being supplied to keep the pressure hull "inflated" is coming from the engine compressors, which at 35000 ft has almost no humidity, and what humidity there is is being extracted by the ...


37

Yes. Fighter aircraft have air conditioning systems. In general, they are called as Environmental Conditioning Systems (ECS). Their primary functions (as far as cockpit goes) include, Cockpit Pressurization Heating/Cooling/air-conditioning Windshield anti-fog/anti-ice The systems usually use conditioned engine bleed air or this purpose. The cockpit air ...


37

Temperature stratification is a vexing problem on lots of airliners. The big challenge is you need a distribution system that is effective when cooling (on the ground and at low altitude when the weather is hot) and heating (as soon as the outside temperature drops to the point where there is a net heat loss that can't be made up by passenger body heat, the ...


27

Not at all. Cold air tends to go low and hot air high. If the cooled air flow were pumped in from the floor, then what we would have would be customers with cold feet and hot heads, making an already miserable experience even worse. By putting the nozzles above the head, the airline is directing the cooled air on the hottest parts of the masses of bodies ...


18

It means that an electrical switching signal is used to drive the pneumatic or air valves in the air conditioning system. Think about it like this: We want to use our garden hose to push open a cat flap but we want electricity to control the pressure in the hose. We could apply an electrical signal to a motor which opens the tap and lets water come out. ...


18

Why is the air so dry Its in part by design and in part a constraint of the system. All aircraft are at risk of corrosion not just big airliners. So keeping them dry is a good way to cut down on that risk. Even though they use fancy anti corrosive paints these days internal corrosion presents a serious risk as some areas may only be exposed during a ...


16

It's because for the Air Cycle process, to chill ambient air without refrigerant, to work, you have to take really hot high pressure air and and remove most of the heat while keeping the pressure up, so that when you let the pressure drop at the end of the process it ends up way below ambient temperature. So you take air off the engine compressor at some ...


15

What powers the airconditioning on most airliners is APU or main engine compressor bleed, which is being supplied at fairly high pressure, say, 80 psi, and temperature, around 3-400F, to the air conditioning packs. You normally have a choice to select APU or main engine bleed. You will obviously use APU bleed on the ground before engine start, but also may ...


14

From second-hand experience (I can say I am really close with a Tornado pilot), the Tornado has a compressor stage airbleed that directs some cold air directly in the cockpit. He would describe it as a direct blast of air in the middle of your stomach, without any possibility to direct it elsewhere. To answer your question, then, we can say that at least ...


13

Quick Introduction to the Airconditioning Unit In the A7-E the air-conditioning system takes high pressure bleed air and passes it through the primary heat exchanger. After here it enters compressor wheel section of the a/c unit, where the heat exchanger reduces the temperature of the bleed air. The A7-E cockpit temperature is maintained either manually ...


10

It seems this is a fairly new issue cropping up and I have been able to find some credible research on the topic (i.e. from official aviation authorities and not news outlets or lawyers websites...) but all of it is pretty recent. The CAA seems to be aware of the issue and has some information on it here. The two studies they link were published in 2017 so ...


9

The AVHerald article you linked to pretty much as the answer to your question: How common are they?Nearly 2,000 events a year in the US alone. [According] to the Kansas State University Research there have been 5.3 fume events per 24,000 daily flights in the USA or 1955 fume events a year. However, only 6 fume events per year get reported to the FAA. ...


9

200 humans exhaling persistently in an enclosed, relatively warm, high pressure atmosphere creates large quantities of condensation on the cold interior surfaces & structure of the aircraft hull, creating a serious corrosion liability. Like computer mainframe facilities being carefully air conditioned & temperature controlled, de-humidifying the air ...


9

Here's an answer for the B737, from own work compiled from several public sources. The A320 and other airliners are very similar. The air conditioning packs are Air Cycle Machines (ACM) which remove heat from air through a reverse Brayton cycle. Hot compressed air is cooled and then expanded, which drops the outflow temperature to a temperature cold enough ...


8

The problem is pressure. In order to use outside air for the cabin, it needs to be pressurized. Otherwise you could not reach higher pressures inside the cabin than outside. The advantage of using bleed air is that this air is already pressurized, so you don't need to do any additional work. It is however too hot to be used as cabin air directly, so a PACK (...


6

In General, Yes. As your image already shows, the same air is distributed throughout the cabin and the flight deck. For example, in the 737 NG FCOMv2 2.30.4 (Air Systems - Air Conditioning Description) it says: Since the flight deck requires only a fraction of the air supply provided by the left pack, most of the left pack air output is mixed with the ...


5

Taking the B737 as an example, fresh air from the left pack flows directly into the cockpit (green airflow in the diagram), whereas the passenger cabin is served from the mix manifold only (yellow). Therefore pilots receive 100% fresh air while passengers receive a mix of 50% fresh air and 50% re-circulated cabin air on average, across all aircraft types ...


5

(wikimedia.org) You have misinterpreted the text. Given that the DITCHING pb is not pushed, the RAM AIR pb opens the emergency ram inlet. The differential pressure (DP) being above or below 1 psi is for the outflow valve (not the inlet). If the DP < 1 psi, the outflow valve opens—this is the opposite to the former title (now the first line) of the ...


5

As an addition to the other answers I want to mention that feet tend to stink - especially when lots of passengers take their shoes off. You don't want that stink to rise from the bottom to the top, where people can actually smell it, so you have the fresh air comming from the top and the stinky air being sucked away at the bottom.


4

They're called "magnet valves". They're basically a valve that's operated by a solenoid. Also seen on locomotive electrical contactors. The solenoid admits air, which moves an air piston which physically actuates the device. Doing that pure electrical would require gigantic solenoids, heavier wiring, heavier generator. One thing to note is that unless ...


4

(1) How can can other fluids contaminate the bleed air? Engine Oil: The engine fan and compressor stages are rotating pieces of metal on metal and thus need lubrication. Engine oil is used for this purpose and could come into contact with the bleed air in case of a leakage (see mooveaviation.com for details). Hydraulic Fluid: Some components of the engine, ...


3

You might have been smelling cooked turbo oil. Leaking seals can potentially allow oil traces into the compressor bleed discharge, especially on auxiliary power units. The other possibility is cooked deicing fluid, which is quite common. Turbo oil and deicing fluid are the two major sources of petrochemical cabin stink. Another possibility would be an ...


2

Far as I can tell, there are no passive or active air quality monitoring devices on the A320. The cabin air systems on modern airliners are designed against an air quality standard, and their performance is tested with equipment that is installed on the test aircraft for that specific purpose. EASA published the results of an air quality campaign test ...


2

Please read carefully ... Extract taken from my FCOM, Info accurate at January 2020: An emergency ram air inlet ventilates the cockpit and cabin to remove smoke, or if both packs fail. The emergency ram air inlet valve is controlled by the RAM AIR pushbutton on the AIR COND panel. This pushbutton opens the ram air valve, provided that ditching is not ...


2

When transporting animals, particularly larger (zoo, show) animals, it is often requested by the handler/vet to have higher pressure altitudes. This helps calm the animal, and makes them less active. In contrast, for long medvac flights, it was company practice to keep the cabin pressure altitude as low as possible, unless the medical personnel requested ...


2

You want the lowest pressure that can be tolerated by most of the population for the purpose of maintaining adequate blood oxygen levels, which is generally considered to be 8000 ft above sea level. At 8000 ft, someone with degraded lung function, like a smoker, is effectively at 10000 ft plus and is already at the threshold of having marginal blood oxygen ...


2

It's not a normal A/C unit Aircraft do not use a Freon based compressor vapor-liquid transition heat pump type arrangement the way every home, car, boat and train does. They use a simpler cycle, because most turbine aircraft have a great abundance of compressed air available, or are obliged to have compressors anyway for pressurization. The compressed-air A/...


2

The running engines power commercial airliner interior climate and environmental control through their built in electrical generators and bleed air systems. The units that supply the interior air in the correct temperature and pressure for passengers are sometimes called PACK as an acronym for Pneumatic Air Cycle Kit. When the engines are off, the APU (...


1

The humidity inside the plane has three constraints: at what point does the humidity become a corrosion risk for the plane? The 787 and presumably other future planes are now mostly "plastic" (composites) and can't corrode, so this limit is just in the process of increasing rapidly. what the hardware can in theory deliver: air at altitude is cold, and ...


1

I can confirm that similar air distribution systems also exist for: Boeing 777: The flight deck receives 100% fresh conditioned air from the left pack. The flight deck is maintained at a slightly higher pressure than the passenger cabin to prevent smoke and objectionable odors from entering the flight deck. (source: 777-200 FCOMv2 2.20.3 Air Systems - ...


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