What are the engine requirements for using an alternate airport?

For using an alternate airport, one of the key requirements relates to the amount of fuel that an aircraft must have when it arrives at that alternative location. The requirement generally stipulates that an aircraft must have enough fuel to reach the alternate airport and, if necessary, to hold for a reasonable amount of time before landing.

In the context of two-engine aircraft specifically, the regulations help ensure safety and allow for single-engine performance capabilities in case of an emergency during flight. For two-engine aircraft, the restriction of needing to be within one hour of the alternate airport highlights the need for immediate availability of sufficient alternate landing options, should an engine failure occur or other operational challenges arise.

This one-hour window is structured to ensure pilots have the ability to respond to in-flight issues with adequate planning regarding fuel, distance, and performance. Therefore, the option that states two engines must be under one hour aligns with these regulatory requirements, reflecting the additional caution needed in multi-engine operations.