Well, here's another question, then. Where do the common identifiers used
for major commercial aiports come from? For instance, Heathrow is LHR on
baggage tags and airline systems, but I don't think it's ICAO identifier is
ELHR. Same queston for BOS, LAX, PHI, etc.

Shawn

"Retro Pilot" wrote in message
...
how long has it been since airports have gone from 3-to-4 letter
identifiers?

also, when did ATC go from 2000 feet vertical separation above FL290 to
1000 feet?

and, no, I was not doing time in prison for the past 20 years for
trafficking.