What is cross-bleed starting and when might it be used?

• A. Starting one engine using bleed air from another source (APU or engine).
• B. Starting one engine using bleed air from another source (APU or engine).
• C. Starting the APU using bleed air from the external air.
• D. Starting two engines simultaneously without bleed air.

Answer: (B)

Cross-bleed starting means using bleed air from a different source to start an engine. That source is usually another running engine or the APU, which provides the pneumatic power to drive the target engine’s starter via the cross-bleed valve.

This method is used when you need to start one engine but don’t have or don’t want to use its own air supply. For example, if one engine is already producing bleed air, you can hook the other engine up to that source through the cross-bleed path so the starter spins the engine until it can sustain itself, or you can use the APU bleed if the other engine isn’t supplying air. It’s a practical way to start an engine without external pneumatic equipment, and it’s common in multi-engine aircraft operations.