Why do commercial flights when talking to ATC use their flight number instead of their tail number? Is it because 278 (two-seventy-eight) is easier to say than 3NW (three-november-whiskey)? Or…
(After pika1000 and damiross post you guys can look at this thread!) 
Believe it or not, I have wondered the same thing myself.
in bad English accent A good question, my man…
I believe it makes it easier to change which aircraft goes on a flight. Rather than re-file the flight plan which, for example N774UA was scheduled to fly and got delayed and so N775UA has to do the flight, they can then swap aircraft without having to bug ATC (and given the sheer number of delays on a daily basis, this could be a nightmare if the clearance/delivery position is filled with radio traffic sorting out which aircraft is on what flight plan.)
Another reason I can think of is that airlines tend to have the registrations with similar groupings of numbers and letters, which would force ATC instead of saying “United 5UA” to say “United 775 Uniform Alpha” if United 774UA happens to be on the same frequency.
A final reason I could think of is unlike your usual GA aircraft, where the pilot flies the same plane often enough that they should be able to remember off the top of their head any portion of their registration number for use with ATC, a typical airline pilot will be on any number of different registrations from one day to the next, even when flying the same leg. So again, much easier for all involved to remember “United 775” than “United 3UA” or “United 223UA” or “United 777UA” 
Wow! Odog1999 nails it three out of three!
Commercial flight plans are filed with the flight number filled in where a GA pilot would fill in the N number.
(Hey Odog! Does your “handle” have any reference to USAF and USA FO pukes?) 
Regards,
James
No, I simply picked “Odog” as a handle, then added 1999 as it was the year I picked up this particular one.
OK, thanks for the info.
Regards,
James
See FAA Publication 7340.1, Contractions for all you want to know about FAA contractions.
In short, airlines and other aircraft operating entities use callsigns for efficiency in communications.
Fascinating.
Nothing whatsoever to do with this topic, but fascinating none the less.
James
[quote=“JHEM”]
This document contains the requirements for the telephony deisgnators (callsigns) used by aircraft operating agencies. Here’s a couple of relevant sections (emphasis mine):
Section 4. CIVIL AIRCRAFT-COMPANY THREE-LETTER IDENTIFIER AND/OR TELEPHONY DESIGNATOR ASSIGNMENTS
1-4-1. DEFINITIONS.
a. This section identifies the criteria for eligibility and procedures for requesting the assignment of an International Civil Aviation Organization (ICAO) three-letter identifier and/or telephony designator for aircraft operating agencies, aeronautical authorities, and air operational services.
b. A three-letter identifier, which when used in conjunction with the flight number, serves as the aircraft identification in the air traffic control system in flight plans, fix postings, control messages, computers, etc. When authorized, the identifier/flight number combination is used instead of the aircraft registration number. Three-letter identifiers are applicable to ICAO assignments for commercial domestic/international aircraft operations, national record communication purposes and air traffic operational Service related functions.
c. A telephony designator, normally the company name or an abbreviation thereof, used in combination with the flight number is usually assigned simultaneously with the three-letter identifier and becomes the aircraft identification in all voice communications with air traffic control facilities. It is also used for telephone coordination purposes.
1-4-5. BASIS FOR ASSIGNMENT.
a. ICAO three-letter identifiers and/or radio- telephony designators are assigned when it is deemed advantageous to the U.S. air traffic control system.
b. ICAO three-letter identifiers and/or radio- telephony designators will not be assigned to eliminate problems which can be resolved by changing registration number, or similar sounding company names. However, due to the vastly growing flying aviation community, modifying a similar sounding telephony designator will not be an uncommon technique. In the interest of safety to the air traffic control system and operationally appropriate albeit FAA standards, adjustments can be made via this procedure.
That’s great if you want to know how the identifiers are derived, but it doesn’t answer the WHY that was originally asked.
Regards,
James
Original question:
Why do commercial flights when talking to ATC use their flight number instead of their tail number?
Why the flight number (which actually consists of the callsign (e.g. United or Cactus) followed by the flight number) is contained in FAA 7430.1, paragraph 1-4-5a: “ICAO three-letter identifiers and/or radio-telephony designators are assigned when it is deemed advantageous to the U.S. air traffic control system.”
Breakdown of this simple paragraph:
ICAO: International Civil Aviation Organization
three-letter identifiers: A three letter code such as UAL or AFR which is an abbreviation of the aircraft operating agency.
radio-telephony designator: The callsign used to identify a specific operating agency. Examples include United (United Air Lines), Cactus (America West)
deemed advantageous: efficient
In other words, the reason for airlines and other aircraft operators, as I stated earlier, is for the efficient operation of the air traffic control system.
By using callsigns instead of the registration, it is possible for an airline to have canned flight plans. Why? Because it is rare for the same aircraft to operate a given flight with the same airplane day after day. Using a callsign allows for only one canned flight plan to be filed with ATC.
odog1999’s post also says basically the same thing that I just said:
I believe it makes it easier to change which aircraft goes on a flight. Rather than re-file the flight plan which, for example N774UA was scheduled to fly and got delayed and so N775UA has to do the flight, they can then swap aircraft without having to bug ATC (and given the sheer number of delays on a daily basis, this could be a nightmare if the clearance/delivery position is filled with radio traffic sorting out which aircraft is on what flight plan.)
That is the central answer to the question. All regularly scheduled airline flights are in an ATC database so that they do not need to be refiled/reloaded every day; only the exceptions - additions/cancellations - have to be changed. The actual airplane (tail number) operating the flight on any day is of no interest to ATC, only to ‘spotters’
The tail number MIGHT be of some interest to maintenance personnel too.
That would depend on the airline. Some airlines, such as Southwest, use the digits in the registration to identify aircraft while others, such as Continental, have fleet numbers that may or may not reflect the registration number
Heh-heh… I read your first sentence and thought, "Yeah, I guess there may be some airlines that don’t care about maintenance
In most cases, the fleet number is a derivation of the tail number. It may be derived from an old tail number that was reregistered, and in some other cases, the fleet number may not reflect any part of the tail number at all. But, I’m sure that any maintenance worker would be able to cross-reference the fleet number with the tail number.