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Standard/Non-standard altitudes in cross country VFR flying

I was thinking in terms of practicalities in the CTR (see my other posts). I just can’t see any practical differences as far as separation is concerned. In the US there is a difference regarding equipment, which will make it different “for real”, but there is none of that in Europe.

The elephant is the circulation
ENVA ENOP ENMO, Norway

what is the difference between C and D in a CTR. There seems to be none.

In Class D airspace, VFR traffic is not separated from IFR traffic.
VFR is also not separated from other VFR.
Traffic information is passed so that pilots can visually acquire and self separate.

In Class C airspace, VFR traffic is separated from IFR traffic.
But VFR is not separated from other VFR.
Traffic information is passed so that pilots can visually acquire and self separate.

Just wondering why some are C and some are D.

Generally speaking, the busier the airspace or the more complex the operation, the more restrictive the classification. As it gets to a point where pilots cannot self-separate / self-organize. e.g. Class B – everything is separated from everything else.

Class A (VFR-banned) is normally used for:
- The most complex/intense operations in smaller spaces where pilots cannot routinely avoid cloud, or
- To substitute for political, financial or regulatory incompetence, where ATC do not have the capacity, capability or willingness to handle VFR traffic.

Last Edited by James_Chan at 23 Aug 11:59

In the TMA probably, but inside the CTR where IFR and VFR already are separated no matter if it’s C or D. Different entering points and so on. Just wondering why some are C and some are D.

The elephant is the circulation
ENVA ENOP ENMO, Norway

LeSving wrote:

Which brings me back to the original thought of what is the difference between C and D in a CTR. There seems to be none.

Well, I’m not an ATCO but I can imagine situations where it would make a difference. E.g. in class D, a radar controller could allow a VFR and an IFR aircraft to pass each other with 500 ft vertical distance. The risk of collision would still be very low, particularly if the aircraft are pointed out to each other. In class C that would not be allowed.

In particular, I can see ATCOs applying this kind of reasoning in situations where the separation safety margins are stacked on top of each other, e.g. the aircraft are already on diverging tracks and several miles apart horizontally (but still closer than radar separation minima).

Last Edited by Airborne_Again at 23 Aug 06:31
ESKC (Uppsala/Sundbro), Sweden

LeSving wrote:

Which brings me back to the original thought of what is the difference between C and D in a CTR. There seems to be none.

Just as a point of reference, in the US Class C airspace at airports is significantly different in that its the level at which a transponder becomes necessary: a Mode C transponder is required both for entry and to fly overhead whereas Class D does not require any transponder unless otherwise required due to an adjacent Class B airport. Class C in the US is also associated with significant amounts of scheduled service, which in practice means most Class C airports have a separate clearance delivery frequency, not shared with ground, so when departing VFR you collect a heading and squawk code to leave the area before calling for taxi. Conversely at Class D you just taxi out and call ground just before entering the controlled movement area. The tower then approves your departure request before takeoff.

Maybe some other countries implement additional ATC protocols at Class C airports that do not apply at Class D airports.

Yes, probably correct. Which brings me back to the original thought of what is the difference between C and D in a CTR. There seems to be none.

The elephant is the circulation
ENVA ENOP ENMO, Norway

LeSving wrote:

but as number two behind another IFR, is that really correct? It makes me responsible for IFR-VFR separation.

It is entirely correct. As I’ve written before, “separation” has a very specific meaning and in some cases normal separation standards can be reduced at the controller’s discretion and the aircraft are still considered to be separated. This is one of those cases.

ESKC (Uppsala/Sundbro), Sweden

Dimme wrote:

I have been cleared for approach as number 2 behind large jets in class C many times

Yes, that’s how it’s done all the time, but is it correct? C is IFR-IFR and IFR-VFR separation by ATC. When I’m being told I’m cleared final as number two behind another VFR, that is OK, but as number two behind another IFR, is that really correct? It makes me responsible for IFR-VFR separation. Shouldn’t this be class D? I don’t know, the difference is mostly theoretical anyway IMO. Separation is assured because the jet flies much faster than a SEP, not by the SEP “separating itself” from the jet. VFR traffic could possibly be more flexible in D vs C I guess (CTR), but that’s very much up to the individual controller.

The elephant is the circulation
ENVA ENOP ENMO, Norway

I don’t remember the details. Those things have changed gradually and slowly over many years. Had a look, and it seems ENVA is in fact the only controlled airport left today still in C. It also looks like several TMAs now are D, not C. There may be a system in it, but it’s not visible to me

The elephant is the circulation
ENVA ENOP ENMO, Norway

LeSving wrote:

Some 10 years ago maybe, AVINOR wanted to make all airports C airspace, like in Sweden. But due to massive protest, that didn’t happen (if I remember correctly).

Do you know why the protest? There is absolutely no problem with VFR in Swedish CTR/TMA?

ESKC (Uppsala/Sundbro), Sweden
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