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

• A. Starting one engine using bleed air from another engine
• B. Starting one engine using external power unit
• C. Starting using battery only
• D. Starting using hydraulic pressure

Answer: (A)

Cross-bleed starting uses bleed air from a running engine to drive the air start of the other engine through a cross-bleed line and valve. This lets you start a second engine without an external power unit or an independent start system by tapping the first engine’s bleed air to spin up the starter in the second engine. The process typically involves ensuring the source engine is producing sufficient bleed pressure, opening the cross-bleed valve to feed the target engine’s air-start system, then engaging ignition and fuel so the engine airs up and starts. Once the start is complete, the cross-bleed supply is disconnected.

This method is preferred when you want to start an engine using existing bleed air rather than relying on external power or a hydraulic/electrical start system. It wouldn’t apply if you were starting from battery power or using a hydraulic start, nor is it about using an external power unit.