If the left or right engine bleed air switch is turned OFF, what happens to bleed air sent to the pneumatic system?

• A. Bleed air continues to ECS from that side
• B. No bleed air is sent to the ECS from that side, but bleed air remains available to anti-ice
• C. Bleed air is redirected to the other side’s ECS
• D. Bleed air is completely blocked from both ECS and anti-ice

Answer: (B)

Bleed air distribution is split between environmental control (ECS) and anti-ice, with dedicated control paths for each side of the aircraft. When you turn off the bleed air switch for a given engine, the valve to the ECS side on that engine closes, so no bleed air from that engine goes to the ECS from that side. However, the anti-ice path is controlled separately, so bleed air from that same engine can still be available to anti-ice if commanded. That’s why the correct result is that no bleed air is sent to the ECS from that side, but bleed air remains available to anti-ice.