Suppose a general aviation aircraft is operating VFR under part 91. When they call ATC they'd normally use their tail number as the call sign. Something like "November 1-2-3 Foxtrot Uniform." What if they called up as "little piggy 27?" Are there guidelines or regulations about this? Does a custom call sign require anything or can you just make one up?
According to JO 7210.3Y, Air Traffic Organisation Policy, section 4-4-2 there are several requirements from both the FAA and FCC. The FAA requirements are (paraphrased from the JO):
- Comply with FCC regulations (remember that the FCC is responsible for radio communication technical regulations, not the FAA)
- Get FAA approval "to avoid possible duplication or conflict with air−ground call signs assigned on a national basis to other aircraft operators"
The FCC requirements are in 47 CFR 87.107 (not 87.115 as the JO says):
(a) Aircraft station. Identify by one of the following means:
(1) Aircraft radio station call sign.
(2) The type of aircraft followed by the characters of the registration marking (“N” number) of the aircraft, omitting the prefix letter “N.” When communication is initiated by a ground station, an aircraft station may use the type of aircraft followed by the last three characters of the registration marking. Notwithstanding any other provision of this section, an aircraft being moved by maintenance personnel from one location in an airport to another location in that airport may be identified by a station identification consisting of the name of the company owning or operating the aircraft, followed by the word “Maintenance” and additional alphanumeric characters of the licensee's choosing.
(3) The FAA assigned radiotelephony designator of the aircraft operating organization followed by the flight identification number.
(4) An aircraft identification approved by the FAA for use by aircraft stations participating in an organized flying activity of short duration.
In other words, your call sign must be approved in advance by the FAA, otherwise you can't legally use it per FCC regulations. In reality, if you call up ATC as Little Piggy 27 you'll either get a laugh and a "no, seriously?" or - in the worst case - you'll just annoy them.
There are also military call signs in use but I know nothing about them. I do remember being in the pattern while an Air National Guard aircraft out of Memphis, TN was doing touch and goes using the call sign Elvis 1. But I have no idea how that call sign was set up between the ANG and FAA.
From ATC's point of view...
If a pilot calls up as "little piggy 27", the controller may respond initially with "little piggy 27".
When ATC establishes communication with a GA aircraft, they state the prefix "November" followed by the phonetic numbers/letters of the aircraft registration.
As a pilot, you could replace "November" with aircraft type, the model, or the manufacturer’s name, and ATC can respond in kind going forward.
[Info from JO 7110.65, 2−4−20. AIRCRAFT IDENTIFICATION]