What is the APU’s primary role on the A320?

• A. Provide pneumatic bleed air for engine starting and air conditioning, and electrical power when required (ground or in flight).
• B. Provide hydraulic pressure only.
• C. Provide cabin lighting control only.
• D. Provide main engine thrust control.

Answer: (A)

The A320’s APU is mainly a compact turbine that provides two essential functions: pneumatic bleed air and electrical power. The bleed air can be used to start the engines and to supply the air conditioning packs when engines aren’t providing bleed air, or when additional bleed air is needed. The APU also powers electrical systems via its generator, which is useful on the ground when external power isn’t available and can supplement aircraft electrical power in flight if needed. This combination—bleed air for starting and air conditioning, plus electrical power—is why the option describing both roles is the best fit.

The other choices don’t fit because the APU is not used solely for hydraulic pressure, cabin lighting control, or engine thrust control. Those systems have separate primary sources and control paths.