The times I have seen a letter at the end is because due to delays the
airline now has two flights flying with the same flight number.
Obviously this can't be allowed so they just add a letter to one or both
of them.



Laura wrote:
I'm tracking a flight tonight between Boston and Paris. The plane was
delayed on the earlier flight leaving Paris, so of course BOS-CDG is
delayed too. But here's something strange: It seems that the original
flight number was cancelled and a new flight plan was filed with a
letter suffix. So instead of flight Air France 337 [AFR337] it is now
AFR337A. Delta, which has its own (non ATC) flight number as a code
share, doesn't even recognize the changed flight times, probably because
its systems are looking for AFR337.

I've found some flight systems can't even handle the letter suffix. So,
is it unusual to have a letter at the end of a flight number?


References:
http://www.massport.com/logan/a_deta...?flight=AF337A
http://www.flytecomm.com/cgi-bin/trackflight
http://query.adp.fr/HDV/HDV/en/horaires.aspx