6.atc-clearances. ATC Clearances
An ATC clearance is an authorization by Air Traffic Control, for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified traffic conditions within controlled airspace. It is not an authorization for a pilot to deviate from any rule, regulation, or minimum altitude, nor to conduct unsafe operations. The pilot in command remains responsible for the safe operation of the aircraft.
Under 14 CFR 91.173, no person may operate an aircraft in controlled airspace under IFR unless that person has filed an IFR flight plan and received an appropriate ATC clearance. The clearance is the legal authorization to fly in the IFR system.
Standard Clearance Format (CRAFT)
IFR clearances are typically issued in a standard sequence pilots remember with the mnemonic CRAFT:
- C – Clearance Limit. The fix, point, or location to which the aircraft is cleared. Usually the destination airport, but may be an intermediate fix if the full route cannot yet be approved.
- R – Route. The route of flight, including any departure procedure (DP), airways, transitions, and arrival (STAR).
- A – Altitude. The initial altitude assignment and any expected altitude changes (e.g., "climb and maintain 5,000, expect 9,000 one zero minutes after departure").
- F – Frequency. The departure control frequency to use after takeoff.
- T – Transponder. The discrete beacon code (squawk) assigned for that flight.
A typical clearance sounds like: "Cessna 12345 is cleared to Memphis International Airport via the JONESBORO Two departure, then as filed. Climb and maintain 3,000, expect 8,000 one zero minutes after departure. Departure frequency 119.1, squawk 4271."
Readback Requirements
Pilots are expected to read back the entire clearance, especially altitude assignments, headings, runway assignments, and clearances into a hold. AIM 4-4-7 emphasizes that altitude and vector readbacks let the controller verify mutual understanding. If anything is unclear or beyond the aircraft's capability, request clarification with "say again" or request an amended clearance.
Abbreviated Clearances and "Cleared as Filed"
When the route in the clearance matches what was filed, ATC may issue an abbreviated clearance using the phrase "cleared as filed." This does not include the altitude, destination, or DP — those items are still issued explicitly. If a Standard Instrument Departure (SID) is filed or assigned, accepting the clearance means the pilot accepts the textual and graphic procedure, including all crossing restrictions, climb gradients, and initial headings.
Clearance Void Times and Hold for Release
At non-towered airports, ATC may issue a clearance with restrictions:
- Clearance Void Time. The clearance is void if the aircraft is not airborne by the specified time. The pilot must notify ATC within 30 minutes of the void time if not airborne (14 CFR 91.185 reference). Example: "Clearance void if not off by 1430."
- Hold for Release. The aircraft may not depart until released by ATC. The controller will provide a release time and, often, an expected departure clearance time (EDCT).
- Release Time. The earliest time at which the aircraft may depart.
Expect Further Clearance (EFC) Time
When ATC issues a holding clearance or a clearance limit short of the destination, an EFC time is provided. This is the time the pilot can expect further clearance beyond the fix or to leave a holding pattern. In a lost-communications scenario (14 CFR 91.185), the EFC time becomes critical for determining when to depart the holding fix.
Amended Clearances
ATC may issue an amended clearance at any time to resolve traffic conflicts, accommodate weather, or change routing. A pilot may also request an amendment. If an amended clearance cannot be complied with — for performance, weather, or fuel reasons — the pilot must immediately advise ATC with the phrase "unable" and state the reason if able.
Pilot Responsibilities
When accepting a clearance, the pilot in command should:
- Copy the clearance accurately, ideally using the CRAFT format on a notepad or kneeboard.
- Read back all required elements verbatim.
- Verify the clearance is within the aircraft's performance and equipment capabilities (RNAV, DME, RVSM, etc.).
- Question any item that is unclear, ambiguous, or unsafe — controllers expect this.
- Comply promptly with the clearance once accepted, but recognize that emergency authority under 14 CFR 91.3 allows deviation when necessary for safety.
VFR-on-Top and Special VFR
IFR pilots may request a VFR-on-top clearance, which authorizes operation under VFR while on an IFR flight plan, allowing altitude selection above any cloud layer per VFR cruising rules. This requires VMC. Special VFR clearances allow operation in Class B, C, D, or E surface area when weather is below basic VFR — 1 SM visibility and clear of clouds, with specific limitations at night.
A clearance is a contract between the pilot and ATC. Accept it only when it is fully understood and within the aircraft's capability — and never let the readback substitute for genuine comprehension.