Are the AC packs normally on for takeoff?

• A. They are always left on for takeoff.
• B. They are never used for takeoff.
• C. They have no effect on takeoff weight.
• D. They can be turned off to achieve a higher maximum takeoff weight.

Answer: (D)

AC packs use bleed air from the engines to provide conditioned air for the cabin. That bleed air draw reduces engine efficiency and the thrust available for takeoff, while the packs also add system load. When you need to maximize takeoff performance under the current conditions, you can turn the packs off to free up bleed air and reduce the load on the engines, which can allow a higher takeoff weight to be used within the airplane’s performance limits. In normal operations, packs are kept on for cabin comfort, but turning them off is a permitted option to achieve better takeoff performance as needed.