Alphanumeric Flight Numbers

I have noticed in the last year or so that some flight numbers are listed two ways. For example, BAW192 is also listed as BAW92W. It is mostly international flights that have these add flight numbers. Does anyone have an idea why they use thgese alphanumber flight “numbers”?

It’s not “some” numbers, but almost all flights have two different flight numbers displayed, e.g. this one i picked randomly:


I assume it differs based on IACO / IATA code (similar like airports where London Heathrow is either listed as EGGL or LHR)

See also here:

The callsigns used in the air are often deliberately different to the commercial flight number, to avoid situations where there is more than one aircraft in the same area with a similar-sounding callsign. This is for safety reasons (so that radio comms are less likely to be misinterpreted). We display both in this case.

See e.g. Call sign similarity service (CSS) | EUROCONTROL


Additionally, for a given airline that has a certain flight number for a given route, no two aircraft can have the same flight number and callsign active (in the air) at the same time. For example, if VIR155 is a flight from EGLL-KLAS that departed on Monday, if that flight is still in the air at the time the VIR155 departs on Tuesday, they can not have the same callsign, so a letter is appended to the callsign of the second flight, and will keep that letter until that flight lands. So Monday’s VIR155 flight may be VIR155, and while it is still in the air, Tuesday’s VIR155 flight may be VIR155K.