Plain English Meaning

A short code on the flight plan that tells air traffic control what your aircraft can do — what kind of navigation gear, radios, and transponder you have on board. ATC uses that code to decide which routes and procedures they can give you.

Full Definition

A standardized one- or two-letter code filed in the equipment block of an FAA flight plan to indicate an aircraft's navigation, communication, and transponder capabilities. ATC uses the suffix to determine which routes, procedures, and clearances the aircraft is eligible to receive, including RNAV and RVSM operations.

Context Anchor

Seen when filing an FAA flight plan and when checking whether an aircraft can use certain RNAV departures or routes.

Derivation

A 'suffix' is something added at the end. Here it's the letter added at the end of the aircraft on the flight plan to its equipment.