Large nontransport category airplanes: Landing limitations: Alternate airports

When selecting an alternate airport for a large nontransport category airplane under Part 135, you must ensure the aircraft can land and stop within 70 percent of the runway's effective length. This calculation uses the airplane's anticipated weight at arrival time and follows the same assumptions specified in § 135.393(b) for destination airports.

This is a more conservative requirement than the destination airport rule, which allows use of 60 percent of the runway. The tighter margin accounts for the uncertainty of diverting to an alternate—you might arrive in worse conditions than planned, possibly with less fuel to burn off, meaning higher landing weight.

In practical terms, this means your alternate airport needs a longer runway than your destination to legally qualify. You must verify this during flight planning, considering forecast weather, expected arrival weight, and runway conditions. If the airplane can't meet this 70 percent requirement, you cannot list that airport as your alternate.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*