"Aircraft Systems "
Fuel System
Normally aircraft have fuel tanks located in the wings and belly. Each fuel tank has at least two fuel boost pumps and most aircraft engines can mechanically suction feed or gravity feed fuel in the event all electric fuel pumps fail. Fuel can also be fed to any engine from almost any tank. Larger aircraft have fuel dump systems to lighten the load for overweight landings. Fuel quantity gauges have backups and fuel low warning systems. There are also fuel used counters to help monitor consumption.
Hydraulic System
Aircraft have separate and redundant hydraulic systems to power flight controls, flaps, gear, thrust reversers, brakes, spoilers, etc. Each engine has a hydraulic pump and there is also an electric powered hydraulic pump. Some airplanes utilize a wind driven backup hydraulic pump. Most aircraft systems utilize separate hydraulic lines and actuators. There are procedures to compensate for loss of hydraulic systems. For example, if the landing gear won’t extend because of a hydraulic failure, it can be lowered by gravity free fall or manually cranked down. Other systems allow for the transfer of good hydraulic power being applied to the failed side.
Pressurization System
The engines draw in fresh clean air which is compressed in the turbines. That air is fed into the air conditioning systems to cool or warm it as necessary. This conditioned air enters into the cabin through the vents located near every seat. At the back of the plane is an outflow valve which regulates and restricts how fast the air escapes the cabin. The pressurization system is automated and monitored in the cockpit. If the automated systems fail, pilots have control of the outflow valves by manual backups. As compared to other large enclosed spaces such as an office, a jetliner's cabin environment is superior. The air conditioning system in most large buildings provide only 20% fresh air and are rarely equipped with high-efficiency filters like those in jetliners. Besides, you are well above any smog!
Fire Protection System
There are fire protection systems for the engines, APU (Auxiliary Power Unit), cargo compartment, and lavatories. In the cabin there are portable fire extinguishers and protective breathing equipment which can be used by crewmembers while fighting a fire. Pilots are alerted to fires and follow procedures to extinguish the fires. For example, to extinguish an engine fire the pilots can shut off the fuel, hydraulics, electricity, and pneumatics (air) to the engine which starves the fire. The pilots also can discharge special engine mounted fire extinguishers to smoother the fire. There are also special heat and smoke activated fire extinguishers mounted in the lavatories and cargo compartments.