Types of ATC Clearances Explained

What a Clearance Is

The Aeronautical Information Manual (AIM) defines a clearance as an authorization by ATC, for the purpose of preventing collision between known aircraft, to proceed under specified conditions within controlled airspace. It is based on known traffic and known physical airport conditions. It is also explicit that a clearance is not authorization to deviate from any rule, regulation or minimum altitude, or to conduct unsafe operation of the aircraft.

That connects to 14 CFR 91.3(a), which says the pilot in command is directly responsible for, and is the final authority as to, the operation of the aircraft. If a clearance would put you in breach of a rule, or in your opinion in jeopardy, it is your responsibility to request an amended clearance. If you would rather do something different, such as land on another runway or delay, the AIM expects you to tell ATC and to cooperate so you do not disrupt traffic flow.

When a clearance is relayed through an air-to-ground communication station, it is prefixed with "ATC clears", "ATC advises" or "ATC requests".

What an IFR Clearance Contains

The AIM lists the items a clearance normally includes:

• Clearance limit. Normally the airport of intended landing. When it is the airport, the clearance should contain the airport name followed by the word "airport". It can also be a navaid or fix.
• Departure procedure. Headings and altitude restrictions to separate you from other traffic, or a published departure procedure where traffic volume warrants one.
• Route of flight. Normally the altitude and route you filed, although ATC often has to specify a different altitude or route because of traffic.
• Altitude data. Normally an instruction to "maintain" an altitude or flight level. If it differs from the one you requested, ATC will tell you when to expect a change.
• Holding instructions. If you are cleared to a fix other than the destination airport and delay is expected, the controller issues complete holding instructions, an expect-further-clearance time and a best estimate of any additional delay, unless the pattern is charted.

Pilots often memorise this order with the mnemonic CRAFT: clearance limit, route, altitude, frequency, transponder code. It is a memory aid, not an FAA term. A sample in that order:

"November one two three alpha bravo, cleared to Springfield Airport via the Nelson Two departure, then as filed. Climb and maintain five thousand, expect niner thousand ten minutes after departure. Departure frequency one two four point seven. Squawk four three two one."

That is an illustration of the standard order, not a recording of a real clearance.

"Cleared as Filed"

An abbreviated IFR departure clearance is based on the route in your filed flight plan, as long as ATC can approve it with little or no revision. The AIM adds two conditions that catch pilots out. You must not accept an abbreviated clearance if the route or destination of the flight plan has changed since you filed it, and it is your job to say so in your first call for clearance if the plan was amended or cancelled and replaced. The controller will then give you a detailed clearance.

Amended Clearances

The AIM says amendments to the initial clearance are issued whenever a controller thinks they are needed to avoid a possible confliction between aircraft. You may be told to hold or change altitude before you reach the point where standard separation from other IFR traffic would no longer exist. You may not see the traffic that caused it. A reply of "no traffic report" does not mean the amendment was needless.

Readback and Records

When you fly IFR, make a written record of your clearance. The AIM notes that when ATC specifies different or added conditions, it means other aircraft are involved in the traffic situation.

Pilots of airborne aircraft should read back the parts of clearances and instructions that contain altitude assignments, vectors or runway assignments, as a double check between pilot and controller. Include your aircraft identification in every readback and acknowledgment, so the controller knows the right aircraft got the message.

On the Ground

Taxi

Pilots on IFR flight plans should call the control tower on the appropriate ground control or clearance delivery frequency before starting engines, to receive engine start time, taxi and clearance information.

Line up and wait

"Line up and wait" tells you to taxi onto the assigned runway, align with the departure direction and wait for further instructions. The AIM states plainly that it is not an authorization to take off, and its note describes events where pilots read back the instruction correctly and then departed without a takeoff clearance.

Release times and void times

At an airport without a control tower, ATC must issue a departure release or a hold for release. A clearance can carry a void time, after which it is void if you are not airborne. If you do not depart before it, tell ATC as soon as possible. The time allowed for you to notify ATC cannot exceed 30 minutes. Fail to call within 30 minutes of the void time and the aircraft is considered overdue and search and rescue procedures begin.

VFR Clearances

Special VFR. An ATC clearance is required to operate within Class B, C, D or E surface areas when the weather is below VFR minimums. A VFR pilot may request a special VFR clearance, traffic permitting and as long as the flight does not delay IFR operations. All special VFR flights must stay clear of clouds, and for airplanes the flight visibility must be at least 1 statute mile (and ground visibility at least 1 mile when taking off or landing).

VFR-on-top. A pilot on an IFR flight plan operating in VFR weather may request VFR-on-top instead of an assigned altitude. It lets you choose your own altitude or flight level, subject to any ATC restrictions. The authorization must include a top report or a statement that none is available, and a request to report reaching VFR-on-top.

What to Do When You Do Not Understand

Ask. The AIM puts the responsibility for the aircraft on you, and a controller would rather repeat a clearance than watch you guess. Say "say again" for anything you missed, read it back for anything you caught, and request an amended clearance if you cannot comply.

Frequently Asked Questions

Is a clearance permission to ignore the rules?

No. The AIM states that a clearance is not authorization to deviate from any rule, regulation or minimum altitude, or to conduct unsafe operation of the aircraft. If a clearance would cause that, the pilot should request an amended clearance.

What should I read back?

The AIM says to read back the parts of clearances and instructions that contain altitude assignments, vectors or runway assignments, and to include your aircraft identification in every readback and acknowledgment.

Does "line up and wait" mean I can take off?

No. The AIM says LUAW is an instruction to taxi onto the runway, align with the departure direction and wait for further instructions. It is not an authorization to take off.

What does "cleared as filed" mean?

It is an abbreviated IFR departure clearance based on the route in your filed flight plan. You should not accept it if the route or destination has changed since you filed, and you must tell ATC in your first call if the plan was amended or replaced.

Related guides: Aviation Radio Communication: How Pilots Talk to ATC, The Aviation Phonetic Alphabet, Alfa to Zulu, How to Tell if Your Aircraft Has Mode C.