AIM 8/15/19  2. At times, a controller/specialist may be working a sector with multiple frequency assign- ments. In order to eliminate unnecessary verbiage and to free the controller/specialist for higher priority transmissions, the controller/specialist may request the pilot “(Identification), change to my frequency 123.4.” This phrase should alert the pilot that the controller/specialist is only changing frequencies, not controller/specialist, and that initial callup phraseolo- gy may be abbreviated. “United Two T wenty − Two on one two three point four” or “one two three point four, United Two T wenty − Two.” e. Compliance with Frequency Changes. When instructed by ATC to change frequencies, select the new frequency as soon as possible unless instructed to make the change at a specific time, fix, or altitude. A delay in making the change could result in an untimely receipt of important information. If you are instructed to make the frequency change at a specific time, fix, or altitude, monitor the frequency you are on until reaching the specified time, fix, or altitudes unless instructed otherwise by ATC. REFERENCE − 4 − 2 − 4. Aircraft Call Signs a. Precautions in the Use of Call Signs. AIM, Paragraph 5 − 3 − 1 , ARTCC Communications EXAMPLE − 1. Improper use of call signs can result in pilots executing a clearance intended for another aircraft. Call signs should  never be abbreviated on an initial contact or at any time when other aircraft call signs have similar numbers/sounds or identical letters/ number;  e.g., Cessna 6132F, Cessna 1622F, Baron 123F, Cherokee 7732F, etc. Assume that a controller issues an approach clearance to an aircraft at the bottom of a holding stack and an aircraft with a similar call sign (at the top of the stack) acknowledges the clearance with the last two or three numbers of the aircraft’s call sign. If the aircraft at the bottom of the stack did not hear the clearance and intervene, flight safety would be affected, and there would be no reason for either the controller or pilot to suspect that anything is wrong. This kind of “human factors” error can strike swiftly and is extremely difficult to rectify. 2. Pilots, therefore, must be certain that aircraft identification is complete and clearly identified 6. Military aircraft use a variety of systems including serial numbers, word call signs, and combinations of letters/numbers. Examples include Army Copter 48931; Air Force 61782; REACH 31792; Pat 157; Air Evac 17652; Navy Golf Alfa Kilo 21; Marine 4 Charlie 36, etc. EXAMPLE − 1. United Twenty − Five Heavy. 2. Midwest Commuter Seven Eleven. 5. Air carriers and commuter air carriers having FAA authorized call signs should identify themselves by stating the complete call sign (using group form for the numbers) and the word “super” or “heavy” if appropriate. Tango Aztec Two Four Six Four Alpha. 4. Air Taxi or other commercial operators  not having FAA authorized call signs should prefix their normal identification with the phonetic word “Tango.” 1. Bonanza Six Five Five Golf. 2. Breezy Six One Three Romeo Experimental (omit “Experimental” after initial contact). 3. Civil aircraft pilots should state the aircraft type, model or manufacturer’s name, followed by the digits/letters of the registration number. When the aircraft manufacturer’s name or model is stated, the prefix “N” is dropped; e.g., Aztec Two Four Six Four Alpha. before taking action on an ATC clearance. ATC specialists will not abbreviate call signs of air carrier or other civil aircraft having authorized call signs. ATC specialists may initiate abbreviated call signs of other aircraft by using the  prefix and the last three digits/letters  of the aircraft identification after communications are established. The pilot may use the abbreviated call sign in subsequent contacts with the ATC specialist. When aware of similar/identical call signs, ATC specialists will take action to minimize errors by emphasizing certain numbers/let- ters, by repeating the entire call sign, by repeating the prefix, or by asking pilots to use a different call sign temporarily. Pilots should use the phrase “VERIFY CLEARANCE FOR (your complete call sign)” if doubt exists concerning proper identity. EXAMPLE − EXAMPLE − EXAMPLE − Radio Communications Phraseology 4 − 2 − 3