On Jan 4, 6:57*pm, (John Clear) wrote:
Here's the story, when an airline has a through flight (Through a hub
airport), and the inbound flight is running late and the outbound
flight is a different AC (Or another plane and crew can be rerouted),
they will send the outbound flight on time but with a different call
sign. You cannot have two flights in the air at the same time with
that flight number.

So the letter is just randomly assigned then, or procedure varies
by airline?

Varies by airline.
Frank