What is a common source of bleed air for cabin pressurization?

The common source of bleed air for cabin pressurization is from gas-turbine engine compressors. This is because gas-turbine engines operate by compressing air, which is then mixed with fuel and ignited to produce thrust. A portion of this compressed air, known as bleed air, is diverted from the engine to supply various systems on the aircraft, including cabin pressurization and environmental control systems.

Using bleed air from the engines is effective because it is already at a high temperature and pressure, making it suitable for rapidly pressurizing the cabin. This system allows for a reliable and continuous supply of air to maintain cabin conditions during flight, supporting passenger comfort and safety at high altitudes where the external air pressure is significantly lower.

The other options, while related to cabin comfort and environmental controls, do not directly serve as the primary source of bleed air for cabin pressurization.