ATWOnline

Airliners, like other aircraft, carry multiple means of identifying them uniquely. At the factory, they are assigned a "Manufacturer's Serial Number" (MSN), similar in concept to the alphabet-soup VIN (Vehicle Identification Number) on automobiles familiar to those of us in the U.S. In addition, and also like automobiles virtually everywhere, once in service they also receive a registration from the appropriate governmental authority. Often referred to as a "reg" (pronounced with a soft 'g' sound, as opposed to the hard 'g' in "regulation"), or not uncommonly in the U.S., as a "tail number", these identifiers are displayed visibly on the aircraft, to the delight of aircraft spotters everywhere. More