Compliance with Air Traffic Control Clearances


Gain the skills associated with ATC clearances.


This is the required reading for this lesson. Numbers in [brackets] indicate the starting and ending page in the referenced reading material. Read all the pages and sections referenced.

  • Instrument Flying Handbook
    • Chapter 2 - The Air Traffic Control System
      • [2-4 to 2-10] "Communication Facilities"
    • Chapter 10 - IFR Flight
      • [10-3 to 10-5] "Clearances"


The notes below highlight the important parts in the referenced material. Reading the notes without having read the actual referenced material is generally not sufficient to pass the written exam!

IFH - Chapter 2

  • Communication Facilities
    • Flight Service Stations (FSS)
    • Towers
    • Terminal Radar Approach Control (TRACON)
    • Air Route Traffic Control Centre (ARTCC)

IFH - Chapter 10

  • ATC blocks the airspace around uncontrolled fields for arriving/departing IFR traffic
  • Clearance from uncontrolled field includes a "void" time during which
    • No other IFR traffic can depart until first aircraft contact ATC in the air or void time has expired
    • No other IFR traffic can be cleared for an approach until first aircraft contact ATC in the air or void time has expired
  • It is considered courteous to depart VFR and then obtain IFR clearance in the air to avoid blocking the airspace
  • Likewise, if weather and operation requirements permits it, consider cancelling IFR when arriving at destination and land VFR
  • The C-R-A-F-T Acronym can be used for IFR clearances
    • C - Clearance limit; Airport or waypoint where IFR will get cancelled (Cleared to Astoria Airport)
    • R - Route; The route to follow (via the SCAPO7 departure, then as filed)
    • A - Altitude; either an initial climb altitude with instructions when to expect higher or clearance to climb via the departure procedure (climb 7,000, expect 12,000 within ten minutes after departure)
    • F - Frequency; Departure controller frequency (Departure on 126.000)
    • T - Transponder; Code to squawk before starting to taxi (Squawk 2345)
  • Once a clearance is read back it is considered accepted and the pilot must comply with the instructions given in the clearance

Sim Pilot Notes

These notes highlight the differences between simulator and real-world flying. These differences are most often due to simulator limitations or specific VATSIM rules.

IFH - Chapter 10

  • VATSIM is using a "top-down" approach.
    • Pilot obtains a clearance from the "lowest" controller covering the airport. If Delivery is not on-line, check for Ground, then Tower, Departure, Arrival and Centre controllers in that order.
  • FSS controllers on VATSIM usually assume the role of a Centre controller but covering a much larger area (e.g. CZEG_FSS in the Canadian North)
    • If a lower level controller is on-line (Delivery, Ground, etc.) the pilot would obtain a clearance from them - not FSS
  • If there is no Departure/Approach/Centre controller an IFR clearance would often use Departure frequency as Unicom (122.800)
  • If there is no controller covering the field, VATSIM pilots should proceed as if cleared "as filed"
  • All IFR flights on VATSIM are required to file a flight plan

Tomas Hansson (This email address is being protected from spambots. You need JavaScript enabled to view it.)
Chief Flight Instructor, VATSTAR
DISCLAIMER: all information contained herein is for flight simulation purposes only.
March 2021

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