Definition. An ATC clearance is "authorization by Air Traffic Control, for the purpose of preventing collision between known IFR traffic, for an aircraft to proceed under specified traffic conditions within controlled airspace."
 As the definition implies, an ATC clearance can be very simple or quite complicated, depending on traffic conditions. Your departure clearance will normally contain the clearance items outlined in the AIRMAN'S INFORMATION MANUAL under, "ATC Clearance/Separations."
 Examples: A flight filed for a short distance at a relatively low altitude in an area of low traffic density might receive a clearance as follows:

  FASTFLIGHT FIVE FOUR THREE TWO KILO - CLEARED TO DOEVILLE
  AIRPORT DIRECT - CRUISE FIVE THOUSAND.

 The term "cruise" in this clearance means that you are authorized to fly at any altitude from the minimum IFR altitude up to and including 5,000 feet. You may level off at any altitude within this block of airspace. A climb or descent within the block may be made at your discretion. However, once you have reported leaving an altitude within the block you may not return to that altitude without further ATC clearance. When ATC issues a "cruise" clearance in conjunction with an unpublished route, an appropriate crossing altitude will be specified to ensure terrain clearance until the aircraft reaches a fix, point, or route where the altitude information is available. The crossing altitude assures IFR obstruction clearance to the point where the aircraft is on a segment of a published route or instrument approach procedure.

 If a flight plan is filed and the clearance received, through Flight Service by telephone or radio, ATC would specify appropriate instructions such as those which follow:

  ATC CLEARS FASTFLIGHT FIVE FOUR THREE TWO KILO TO SKYLINE
  AIRPORT VIA THE CROSSVILLE ZERO FIVE FIVE RADIAL - VICTOR ONE
  EIGHT - MAINTAIN FIVE THOUSAND - CLEARANCE VOID IF NOT OFF BY
  ONE THREE THREE ZERO.

 Under more complex traffic conditions, you may receive a more involved clearance such as the following:

  ATC CLEARS FASTFLIGHT FIVE FOUR THREE TWO KILO TO WICHITA
  MID-CONTINENT AIRPORT VIA VICTOR SEVEN SEVEN - LEFT TURN AFTER
  TAKEOFF - PROCEED DIRECT TO THE OKLAHOMA CITY VORTAC - HOLD
  WEST ON THE OKLAHOMA CITY TWO SEVEN SEVEN RADIAL - CLIMB TO
  FIVE THOUSAND IN HOLDING PATTERN BEFORE PROCEEDING ON COURSE
  - MAINTAIN FIVE THOUSAND TO CASHION INTERSECTION - CLIMB TO
  AND MAINTAIN SEVEN THOUSAND - DEPARTURE CONTROL FREQUENCY WILL
  BE ONE TWO ONE POINT ZERO FIVE - SQUAWK ZERO FOUR ONE TWO.

 None of the foregoing clearances are especially difficult to copy, understand, and comply with - assuming that you -
  a. Have properly tuned your radio.
  b. Are concentrating on what you hear.
  c. Can copy fast enough to keep up with the clearance delivery.
  d. Are familiar with the area.

 Suppose, on the other hand, that you are awaiting departure clearance at a busy metropolitan terminal (your first IFR departure from this airport). On an average date, the tower at this airport controls departures at a rate of one every 2 minutes to maintain the required traffic flow. Sequenced behind you are a number of aircraft ready for departure, including jet transports.

 ATC issues you the following "abbreviated clearance" which includes a Standard Instrument Departure (SID) (Fig. 12-2):
  FASTFLIGHT FIVE FOUR THREE TWO KILO - CLEARED TO LA GUARDIA
  AS FILED - RINGOES EIGHT DEPARTURE PHILLIPSBURG TRANSITION
  - MAINTAIN EIGHT THOUSAND - DEPARTURE CONTROL FREQUENCY WILL
  BE ONE TWO ZERO POINT FOUR - SQUAWK ZERO SEVEN ZERO ZERO.

 This clearance may be readily copied in shorthand as follows:

  CAF/RNGO8/PSB/M80/DPC 120.4/SQ 0700.
 The information contained in this clearance for a Standard Instrument Departure is an abbreviation of Air Traffic instructions too complicated and extensive for you to follow and copy, regardless of your proficiency in using clearance shorthand. Study of the route specified in the clearance shows the importance of the Standard Instrument Departure. At common operating speeds in modern light aircraft, the clearance allows no time for extensive reference to your departure chart. You will be too busy flying your aircraft, navigating, and communicating with ATC to familiarize yourself with the clearance data after you have accepted it. You must known the locations of the specified navigation facilities, together with the route and point-to-point time, BEFORE accepting the clearance.
 

 The Standard Instrument Departure, which you have available during preflight planning, enables you to study and understand the details of your departure before filing your IFR flight plan. It permits you to set up your communications and navigation equipment and to be ready for departure before requesting IFR clearance from the tower. The SID eliminates unnecessarily long delays in clearance delivery that would result in inconvenience and expense to airspace users as well a revisions in flight planning for pilots awaiting departure.

 Regardless of the nature of your clearance, it is imperative that you are prepared to understand it, and having accepted it, comply with ATC instructions to the letter. It is your privilege to request a clearance different from that issued by ATC if you consider another course of action more practicable or if your aircraft equipment limitations or other considerations make acceptance of the clearance inadvisable. Though FAR Part 91 does not require you to accept a clearance, it is very specific as to your privileges and responsibilities.

  1. Responsibility and authority of the pilot in command.
   (a) The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.
   (b) In an emergency requiring immediate action, the pilot in command may deviate from a rule to the extent required to meet that emergency.
   (c) Each pilot in command who deviates from a rule shall, upon the request of the Administrator, send a written report of that deviation to the Administrator.
  2. Compliance with ATC clearances and instructions.
   (a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance, except in an emergency, unless he obtains an amended clearance. However, except in positive controlled airspace, this paragraph does not prohibit him from canceling an IFR flight plan if he is operating in VFR weather conditions. If a pilot is uncertain of the meaning of an ATC clearance, he shall immediately request clarification from ATC.
   (b) Except in an emergency, no person may, in an area in which air traffic control is exercised, operate an aircraft contrary to an ATC instruction.
   (c) Each pilot in command who deviates, in an emergency, from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.
   (d) Each pilot in command who (though not deviating from a rule of this subpart) is given priority by ATC in an emergency, shall, if requested by ATC, submit a detailed report of that emergency within 48 hours to the chief of that ATC facility.

 An ATC clearance presupposes that you are equipped and will comply with the applicable Regulations (Part 91), as follows:

  1. Instruments and Equipment IFR Flight. The following instruments and equipment are required:...Two-way radio communications system and navigational equipment appropriate to the ground facilities to be used....
  2. IFR Radio Communications. The pilot in command of each aircraft operated under IFR controlled airspace shall have a continuous watch maintained on the appropriate frequency....
  3. Course to be Flown. Unless otherwise authorized by ATC, no person may operate an aircraft within controlled airspace, under IFR, except as follows:
   (a) On a Federal Airway, along the centerline of that airway.
   (b) On any other route, along the direct course between the navigational aids or fixes defining that route.

 However, this section does not prohibit maneuvering the aircraft to pass well clear of other air traffic or the maneuvering of the aircraft, in VFR conditions, to clear the intended flight path both before and during climb or descent.

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