Hi all,
Because it is so rare relative to the amount of flights I at least pay attention to, I notice occasionaly some flights end with an alpha letter, such as UAL881C. What is the significance of these infrequent alpha endings?
Is it more common across the pond to see this? I though it was anyway, but would like to hear yor thoughts.
Thanks all,
Neil 
As indicated in other postings, they are used to reduce confusion when there are other flights with the same flight number.
Interesting. Ok, thank you for the reply.
Neil
An airline may have a flight with several legs (KIAD - KORD - KDFW). The KIAD to KORD flight may be delayed for whatever reason (weather, maintenance problem, etc.). Rather than wait for the plane to get to KORD, the airline will dispatch another plane already at KORD to go from KORD to KDFW and get those pax out on time. Thus you would have two flights with the same number, but they must be differentiated in some manner.
NN,
Excellent, thank you!!
Neil 
At Airnet if we needed an extra plane b/c we balked out we simply picked up 2 clearances and asked for the second flight to be USC###A. We were able to avoid an extra flightplan that way.
Some international airlines do this as well, such as BAW69V EGLL-KPHL, and SWR9T KORD-LSZH.
Regards
JB