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I ask myself why VFR-traffic has to get ATC-clearances in class D airspace, because as far as I know, ATC doesn’t provide separation for VFR-traffic in this airspace class...

So why for example is a VFR pilot given the clearance (or is that an instruction) to maintain 4000 ft in class D airspace, if he is responsible for the separation, and not the controller?

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  • $\begingroup$ Welcome to aviation.SE! Which country or regulations are you asking about? $\endgroup$
    – Pondlife
    Aug 16, 2020 at 16:05
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    $\begingroup$ Hello, I meant for Luxembourg, which is under the jurisdiction of the EU (SERA) and other, national, regulations. The AIP for Luxembourg is published by the belgian ANSP. $\endgroup$
    – Felix Braun
    Aug 16, 2020 at 18:47

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Because class D is controlled airspace.

While you are correct that VFR-IFR separation is not provided in class D airspace, the major advantage compared to class E airspace is that, because VFR is subject to a clearance, ATC knows exactly where all VFR aircraft are, enabling ATC to provide very accurate traffic information and/or collision avoidance.

So why for example is a VFR pilot given the clearance (or is that an instruction) to maintain 4000 ft in class D airspace, if he is resposible for the separation, and not the controller?

ATC can certainly limit you to a specific altitude, but as a VFR flight ATC can never lock you on a specific heading (since you must also be able to turn to stay clear of clouds). All rules regarding right-of-way in the air are based on turning - not climbing or descending - so being instructed to maintain a specific altitude should not limit your abilities to follow the normal rules of right-of-way.

Although not technically required, ATC will often provide some sort of separation between VFR and IFR in class D, at least in cases where there is an obvious risk of collision. But the normal separation minima do not apply, and ultimatively it is pilot responsibility to practise see-and-avoid (which is made significantly easier compared to class E or below because ATC can provide accurate traffic information).

If we go one step "up" the ladder, to class C - where VFR-IFR separation is provided - a major difference for VFR is the requirement for a mode A/C transponder. A transponder is normally not required in class D for VFR traffic, which is another reason ATC is not necessarily able to provide IFR-VFR separation in class D.

There are different use cases for the different airspace classes, and different countries and ANSP's will make use of them as they see fit in their local environment. The existance of the different airspace classes makes it possible to graduate the service provided to suit most situations:

  • Class G: No separation
  • Class F: No separation, but advisory service
  • Class E: IFR-IFR separation, no radio/transponder for VFR
  • Class D: IFR-IFR separation, radio+transponder required for VFR
  • Class C: IFR-IFR and IFR-VFR separation
  • Class B: IFR-IFR, IFR-VFR and VFR-VFR separation
  • Class A: IFR-IFR separation, VFR not allowed
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  • $\begingroup$ Thanks, that already clarifies it... but where can I specifically find those regulations, apart from the different national AIP’s? $\endgroup$
    – Felix Braun
    Aug 16, 2020 at 18:49
  • $\begingroup$ @FelixBraun ICAO Annex 11, or summarized here: skybrary.aero/index.php/Classification_of_Airspace - but be aware not all countries comply 100% with ICAO recommendations, so the national AIPs for the specific country is always the authoritative source. (AIP section ENR 1.4) $\endgroup$
    – 60levelchange
    Aug 16, 2020 at 19:14
  • $\begingroup$ I‘ve taken a look at some AIP‘s, they all are more or less the same (in terms of airspace classification)... So if I‘m right, ATC instructions given to such VFR traffic are to separate it from other traffic, even if that isn‘t really the task of the controller? $\endgroup$
    – Felix Braun
    Aug 18, 2020 at 12:03
  • $\begingroup$ @FelixBraun In practise, to a small extend, yes. But mainly to be able to provide accurate traffic information $\endgroup$
    – 60levelchange
    Aug 19, 2020 at 6:23

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