The functions of an aircraft's bleed air system include ¹ ²:

- *Air Conditioning*: Bleed air is filtered and cooled before being introduced into the aircraft cabin. The temperature of the air is regulated using uncooled bleed air and the humidity of the mixture is adjusted before being released.
- *Pressurization*: Bleed air is used to pressurize the aircraft cabin, which allows passengers to breathe at high altitudes without oxygen masks.
- *Engine Start*: Bleed air is used to power an air turbine starter motor to start the engine.
- *Water System Pressurization*: Bleed air is used to pressurize the potable water holding tank, eliminating the need for a pump to feed the water to the galleys and lavatories.
- *Hydraulic Reservoir Pressurization*: Bleed air is used to pressurize the hydraulic system reservoirs, reducing the likelihood of pump cavitation and the resulting loss of system pressure.
- *Boundary Layer Enhancement*: Bleed air is used to enhance boundary layer energy, increasing the stalling angle of attack and the maximum lift coefficient by delaying boundary layer separation from the airfoil.
- *Anti-Ice*: Bleed air is used to heat the surface of the wings, tail surfaces, and engine inlets to prevent ice accretion.
- *De-Icing*: Bleed air is used to inflate pneumatic boots on the leading edge of the wings to break off any unwanted ice.