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.
Research Notes
AIM 4-4-4 covers IFR clearances on takeoff — the procedure when ATC issues an IFR clearance to a pilot already taxiing or in the runup area.
The pre-departure IFR clearance: Pilots typically obtain the IFR clearance from Clearance Delivery (or via phone if no Clearance facility) BEFORE taxiing. The clearance includes the full CRAFT (clearance limit, route, altitude, frequency, transponder).
The 'void time' clearance: Used at non-towered airports without immediate Center coverage. The clearance specifies a takeoff window: "Cleared as filed, climb and maintain 7,000, clearance void if not off by [time], if not off by [time] contact Center within 30 minutes."
Pilot obligations on void-time clearance:
- Take off before the void time, or
- If departure is delayed, call Center immediately to extend or cancel
- Failure to depart on time without notifying ATC triggers SAR procedures
The 'cleared as filed' shortcut: If you filed an IFR flight plan and ATC issues "cleared as filed," you're authorized to fly the route exactly as filed. Modifications to the route will be stated explicitly.
Reference: § 91.173 (IFR clearance required); AIM 4-4-4; AIM 5-1-9 (Departure Clearance).