What does it signify when the bleeds are closed?

When the bleeds are closed, it signifies that the system is configured to optimize performance by not using bleed air from the engines or auxiliary power unit (APU). This configuration allows for the most efficient use of engine thrust and supports specific operational needs during takeoff. In this context, having the APU on for takeoff ensures that the aircraft can provide necessary electrical and pneumatic power while maintaining optimal engine performance.

The closed bleeds typically indicate that the aircraft is ready for takeoff with the APU functioning, allowing the aircraft systems to operate effectively without taxing the engines. This is particularly relevant in ensuring that the pressurization and environmental control systems are managed properly during the critical phases of flight like takeoff.

In contrast, if the APU were not operational or OFF during takeoff, there would be limitations on the functions that the aircraft systems could perform, which could adversely impact safety and operational effectiveness.