AIM Text
- Amendments to the initial clearance will be issued at any time an air traffic controller deems such action necessary to avoid possible confliction between aircraft. Clearances will require that a flight “hold” or change altitude prior to reaching the point where standard separation from other IFR traffic would no longer exist.
- A pilot may wish an explanation of the handling of the flight at the time of occurrence; however, controllers are not able to take time from their immediate control duties nor can they afford to overload the ATC communications channels to furnish explanations. Pilots may obtain an explanation by directing a letter or telephone call to the chief controller of the facility involved.
- Pilots have the privilege of requesting a different clearance from that which has been issued by ATC if they feel that they have information which would make another course of action more practicable or if aircraft equipment limitations or company procedures forbid compliance with the clearance issued.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-4-4.
The short answer
This AIM section is FAA advisory guidance on amended clearances, which controllers issue whenever needed to avoid possible confliction between aircraft. It explains that a flight may be told to hold or change altitude before standard separation would be lost, and that pilots may request a different clearance. It supports ATC compliance under 14 CFR 91.123.
Research Notes
Common Questions
Why did ATC amend my clearance when there was no traffic reported?
The AIM explains amendments are issued any time a controller deems action necessary to avoid possible confliction. A reply of no traffic report can occur because the controller acted to prevent a confliction that would have occurred at a distant point, so the conflicting traffic was never near your present position.
Can a pilot request a different clearance than the one ATC issued?
Yes. The AIM states pilots have the privilege of requesting a different clearance if they have information that would make another course of action more practicable, or if aircraft equipment limitations or company procedures forbid compliance with the clearance issued.
How can a pilot get an explanation of an amended clearance?
The AIM notes controllers cannot take time from immediate control duties or overload ATC communications channels to explain at the time. Pilots may obtain an explanation by directing a letter or telephone call to the chief controller of the facility involved.