When are reduced thrust takeoffs prohibited?

Reduced thrust takeoffs are prohibited when cowl and/or wing anti-ice is selected on because the use of anti-ice systems increases the engine throttle demand to ensure appropriate thrust and performance under potentially icing conditions. This means that the engines need to operate at a higher thrust level to account for the additional drag and other performance impacts associated with ice accumulation on the wings or in the engines. Utilizing reduced thrust in this situation could compromise safety and aerodynamics, thereby inhibiting the aircraft's ability to accelerate sufficiently, maintain control, and achieve the necessary performance for takeoff.

In contrast, reduced thrust takeoffs may still be permissible in other situations, such as when the anti-ice is off, the outside air temperature exceeds 15°C, or when the runway is dry, as these factors do not adversely affect the aircraft's performance capability. In these scenarios, the engines can be set to a reduced thrust setting because the potential for performance restrictions linked to icing is eliminated or minimized.