Aircraft Systems

The most important one from a physiological point of view is pressurisation, because we need to be able to breathe air to survive … air is pumped into the cabin to supply enough oxygen at the right pressure for us to breathe. The pressurisation system in modern aircraft is very sophisticated compared with planes of the ’80s and ’90s. You shouldn’t feel any change of pressure in the cabin with the possible exception of taking off and starting to descend. Modern systems are automatic and reliable.

Unfortunately for nervous passengers who enjoy a breeze over then modern air conditioning on aircraft does not give individual air vents like the ones pictured here. It’s always worth carrying a little battery operated fan with you if you want the feeling of fresh air on your face. 

After that we need to be comfortable so we need to be warm … we do that in connection with the pressurisation system. As the air is pumped into the cabin it goes through a heat exchanger to warm it. The outside air temperature is about -65 Centigrade (your Deep Freezer works at about -10 Centigrade)…  so the air certainly needs warming!

Your food needs heating or cooking (First Class) so we need electricity. You want to be entertained so we need more electricity. The electricity comes from generators on the engines. There are standby supplies from other sources (at least three) and there is a battery that will last long enough for the plane to land. Electricity is required in the cockpit for the flight instruments and navigation equipment, and this takes priority over any other system … even the IFE

As your pilot, I need to control the plane,  for example, raise and lower the wheels or use the flaps so the plane needs hydraulic power. Hydraulic power sounds technical but is the sort of thing on your car that gives you power steering. We use this system for the brakes as well. Once again if the main systems fail there are numerous backups. After this, there is power available from the RAT ( See Glossary).

Most of these services are also needed on the ground when the engines aren’t running and to provide it there is a small engine that can do these things .. it’s called the APU ( See Glossary).

That’s pretty much all the stuff we need.  All this is supplied from the engines … and if you think there’s something dangerous about relying on the engines for all this important stuff then consider your car engine … it does all the same stuff and you never give it a thought. But even worse than that you never check it, and how often has it ever stopped?

I won’t leave you worrying about if an engine stops and the plane is left without some of these ‘services’, so I shall deal with that now. On a two-engined plane, each engine will have a generator to supply electricity, each engine will have a pump to supply hydraulic power and each engine can pump air into the cabin. The APU can supply electricity and air so connecting these will make the plane ‘normal’ again with two of everything.
So if an engine stops we can restore everything back to normal. A plane with four engines does the same. If there is a problem with any system we start to share things. In other words, rather than make all the normal demands on the services we’d turn off the less important ones. I bet you didn’t realize it was this simple?