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Some clearances are only provided after specifically requesting them, such as the departure, engine-start, taxi or oceanic crossing clearance. Line-up and Take-off clearances are issued once the pilot relays to be ready for it (this could be viewed as "actively requesting" the clearances.

As I have learned after this question, sometimes descent clearances are issued by ATC without the pilot asking for it. Which other clearances are issued "automatically"? Specifically, I'm asking about the approach clearance and the landing clearance.

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  • $\begingroup$ I receive clearances into class B without requesting them. Usually a controller being nice and eliminating a shelf as an obstacle to a climb. I'll also receive clearances for "the option" when doing touch and gos without a request. $\endgroup$ – acpilot Feb 10 '17 at 2:43
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No clearance is issued without the pilot requesting it. But a request is not just something you do on the radio. The interesting questions here is: how do pilots request something?

The most common way is through a flight plan. By filing a flight plan, the pilot details the planned flight, from departure to destination, via a predefined route, with a requested speed and level. ATC will issue a flightplan clearance prior to departure or prior to entering controlled airspace. This covers the general flight, and basically lets the flight take place.

During the flight, specific details need to be requested by the pilot - such as taxi - but only if the controller is not already aware that the flight is ready for whatever it is they are requesting. For example, during radar vectors for approach, ATC already knows that the flight is requesting approach at their destination (since the destination is noted in the flightplan), so ATC will clear the flight for approach without needing the pilot to explicitally request it. Same goes for landing clearance. The pilot does not have to explicitally say "request to land", because this is already a part of the flight plan. ATC will automatically issue a landing clearance when appropriate.

ATC can issue instructions or clearances to flights that deviate from their flightplan if needed for safety or efficiency reasons. For example, ATC may instruct a flight to change level due to traffic ahead on the same level. But the flight plan is always the basis for all clearances.

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    $\begingroup$ good explanation, thank you! $\endgroup$ – Stefan Feb 7 '17 at 19:02
  • $\begingroup$ As I commented on the question, ATC often gives me takeoff or route clearance without any request. Is this a difference of rules. $\endgroup$ – J Walters Feb 7 '17 at 19:12
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    $\begingroup$ @JonathanWalters Your request is you submitting a flight plan. By submitting your flightplan, you request to fly in accordance with that flightplan, so you do not have to detail your request on the radio $\endgroup$ – J. Hougaard Feb 7 '17 at 19:16
  • $\begingroup$ OK, and I suppose by the same logic, my taxi request to ground is sufficient initiation for Tower to issue my takeoff clearance even though I may not have contacted them? $\endgroup$ – J Walters Feb 7 '17 at 19:33
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    $\begingroup$ @JonathanWalters Exactly. Essentially, they already know who you are and what you want, so you don't have to tell them $\endgroup$ – J. Hougaard Feb 7 '17 at 19:40
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ATC "clearance" is only used in specific situations:

  1. A route clearance - pilots request this when ready
  2. Takeoff clearance - pilots assumed to be ready unless they say otherwise
  3. Approach clearance - ATC provides this once the aircraft is positioned
  4. Landing clearance - ATC provides this when ready

All of these are very important details of the flight, and avoiding using the word "clearance" in other situations prevents confusion about what ATC has cleared the pilots to do. (There are others but for the typical commercial flight these are the main ones)

Anything else would be an instruction from ATC. Pilots may make requests but are expected to follow these instructions unless they feel that it would compromise safety.

Before the flight, the pilot will request their route clearance. ATC will respond by clearing them to fly to their destination via a certain route. This is usually the only clearance pilots receive before takeoff.

The pushback will be requested by the pilot. At large airports ATC may coordinate gate operations but this is not technically a clearance, but an instruction of when and where to push. The ground crew may let the pilot know when they can start their engines, but again this would be an instruction.

Taxi will be requested by the pilot, but again ATC will give them instructions, not a clearance. When crossing an active runway, ATC will give an explicit instruction to either cross or hold short of the runway. This is not a clearance but pilots should repeat these instructions back to ATC to help prevent runway incursions.

Upon reaching the runway, especially at a busy airport, the pilots are assumed to be ready. If not they must inform ATC. ATC will then give the pilots their clearance for takeoff. At a less busy airport ATC may wait for the pilots to request clearance. Depending on traffic, ATC may give a "line up and wait" instruction. Then the pilots will be cleared for takeoff.

Once in the air the pilots are expected to fly the route that they were cleared for. Depending on conditions, pilots may request or ATC may offer certain shortcuts or deviations from their route. This could be just a temporary vector. ATC may also clear them to a certain navigation point, but this changes their clearance limit. They are no longer cleared for the rest of the route, only up to where this amended clearance ends. ATC must provide further instructions, which could be as simple as "and then on course".

Changing altitudes are instructions from ATC. ATC will instruct the pilots to climb to the altitude indicated on their flight plan, depending on conditions. Pilots may request altitude changes for weather or performance reasons. Once nearing top of descent, pilots can request descent if ATC hasn't allowed it yet.

Arrival procedures will often require ATC instructions to get the pilots lined up with a runway. ATC will provide them vectors and altitudes. ATC will then clear the pilots to fly an approach to a certain runway. Although pilots may request a certain approach procedure, ATC will decide when to provide the clearance.

Once the aircraft gets closer to the runway, ATC will give clearance to land. The pilots shouldn't have to ask unless they are unsure of their clearance or the tower seems to forget it. If the pilots aren't cleared to land by a certain point, they must follow any missed approach instructions that are given in the approach procedure they were cleared for or by ATC.

Once on the ground, the pilots will receive instructions for taxiing to the gate.

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    $\begingroup$ Taxi instructions are not a clearance with one exception, according to the AIM 4−3−18. Taxiing 4. 5. A clearance must be obtained prior to crossing any runway. ATC will issue an explicit clearance for all runway crossings. $\endgroup$ – JScarry Feb 7 '17 at 21:17
  • $\begingroup$ @JScarry The AIM calls it a clearance but it's more of a special instruction, I'll edit to try to clarify that bit. $\endgroup$ – fooot♦ Feb 7 '17 at 21:57
  • $\begingroup$ An ATC clearance is needed to enter Class B Airspace $\endgroup$ – Steve Kuo Feb 9 '17 at 6:15
  • $\begingroup$ @SteveKuo yes, that's one of the additional clearance I left out, airliners are typically on IFR plans in contact with ATC and so don't need an explicit clearance. $\endgroup$ – fooot♦ Feb 9 '17 at 15:19
  • $\begingroup$ This question and this forum is not specific to airliners/IFR $\endgroup$ – Steve Kuo Feb 17 '17 at 0:35

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