Lstc From Canada, joined Jun 2003, 320 posts, RR: 0 Reply 2, posted (9 years 9 months 6 days 4 hours ago) and read 1239 times:
It depends....do you want to navigate to the airport or some co-located navaid that uses the identifier.
Three letter identifiers for airports are a tool for travel agents and airline check-in clerks. In the cockpit, if its an airport you put "K" in front for airports in the continental US. (C for Canada).
An example is if you type BOS as a waypoint, you will be directed to a VOR, not Boston's Logan Airport. If you type in KBOS, you will be directed to the center of the longest runway at Boston's Logan airport.
Many FMC data bases don't contain smaller airports and others have pilot selectable filters to inhibit the selection of airports meeting some minimum criteria such as runway length.
Jetguy From , joined Dec 1969, posts, RR: Reply 3, posted (9 years 9 months 6 days 2 hours ago) and read 1217 times:
It all depends upon the database installed in the particular FMS. Many databases, for high-performance aircraft, are limited to airports with runways greater than say 4,000 or 5,000 feet in length. This would exclude many, but not all, of the "alpha-numeric" airports. As for the rest, yes, you only need to enter the alpha-numeric ID, such as 4I3, 43V, etc.