Why is Skywest using some non-numeric flight numbers, like “40R”? They are used for ATC purposes, not the schedule.
They probably have more than one flight with the same number. United and Delta probably dictate their flight numbers. Controllers also advise aircraft and airliners if there are other aircraft on the freq with similar tail numbers or call signs.
This is not why they are using letters. They used to run their whole schedule with four-digit numbers, but now they are two digit numbers with a letter at the end. Why the change?
I do not believe that Delta and United dictate their flight numbers.
In my experience, controllers often fail to advise aircraft of others on the frequency with similar tail numbers. In fact, I once heard an airplane check in with the exact same call sign as mine (it was military, I was civil), and the controller did not catch it.
They probably have more than one flight with the same number. United and Delta probably dictate their flight numbers. Controllers also advise aircraft and airliners if there are other aircraft on the freq with similar tail numbers or call signs.
Jeez, give the guy a break for trying to answer your question!
“hey does anyone know why this is?”
-“well, i think it might be a, b, or c”-
“nope, a is wrong, b is also wrong, and c is wrong too.”
flightaware.com/live/flight/SKW6529
flightaware.com/live/flight/SKW6515
flightaware.com/live/flight/SKW5737
flightaware.com/live/flight/SKW6862
flightaware.com/live/flight/SKW5785
flightaware.com/live/flight/SKW5737
flightaware.com/live/flight/SKW4005
Wanna change your answer or do a mobile shout out? The fact is, if you had done some research, is that not all of SKW’s flights end in letter(s).
If you don’t believe me, go to flightaware.com/live/fleet/SKW.
If you don’t know the answer to your question then don’t knock those who do.
I am most familiar with Seattle Center and I always hear them give advisories for similar numbers even when I don’t see how they could be confused. I think this shows extreme professionalism.
Also for example (from United.com):
United Flight 5737
Operated by UNITED EXPRESS/SKYWEST
IN FLIGHT
Details San Francisco, CA (SFO)
Sat, Dec 2
Scheduled: 11:27 AM
Actual: 11:24 AM
Reason: –
Gate: 87A
Chico, CA (CIC)
Sat, Dec 2
Scheduled: 12:19 PM
Estimated: 12:14 PM
Reason: –
Gate: –
Baggage claim: –
Flight 5737
Operated by UNITED EXPRESS/SKYWEST
NOT DEPARTED
Details Chico, CA (CIC)
Sat, Dec 2
Scheduled: 12:39 PM
Estimated: 12:39 PM
Reason: –
Gate: –
San Francisco, CA (SFO)
Sat, Dec 2
Scheduled: 1:36 PM
Estimated: 1:36 PM
Reason: –
Gate: 76A
Baggage claim: 4
The 5000 series flight #'s are our United express Brasilias. The 6000 series dictates a United express CRJ. Be it either a 200 or a 700. As for the Delta Connection side, things are changing constantly. We have Brazees, 200’s and 900’s. With ASA being under SkyWest INC. That also brings in the ATR’s. I’ll let you know when I figure them out. 
Usually, but not always. When they do, they typically say something along the lines of “be advised two aircraft on frequency with simial call signs” and then state the two call signs. From that point, they typically give the full call sign and aircraft type as opposed to just the last three digits. I’ve had a few experiences where the controllers didn’t catch the similar call signs and just pointed it out to them, at which point they use the full call signs and type again.
Skywest began using the letters out of SLC to address complaints by the pilot group and ATC concerning the similarity of flight numbers. Easy to take a call for flight 4933 when you are 4833. Now you are assigned a randomized flight number like SKYW 33J.