Revision number. Sometimes they're changed.

Paintwagon wrote on Jul 20^th, 2012 at 10:32am:


You are correct, the previous answer was a little wrong. SID and STARS are generally named after a reporting point or beacon on the procedure in question. The number comes in where there are several iterations of the procedure but to or from different runways or start/end points (generally runways!), or with navigational variations to/from the point.

For example at airport "X" you may have an SID based on the "ABCDE" VOR. From runway 03 (random runway direction chosen for illustration!), this may be the "ABCDE 1", from Rwy 21, the "ABCDE 3".

You may find you get different variations for differing aircraft performance types (some SIDS/STARS are jet only, some prop only for example, others for aircraft able to make specific climb gradients etc). Often these will get differentiated using a letter to suffix the SID/STAR identifier,

eg, "ABCDE 1Y"