What I was getting at is around post #14 i.e. the ICAO position on VFR in Class D which should apparently be freely given.
Of course the radar controller can see you so in reality it is not an issue, but one needs to somehow formalise that position.
LeSving wrote:
Is it? It obviously can be, depending on airspace and flight rules, but equally obvious it is not the only reason.
Yes. That’s the original context for the use of the word “clearance”. It’s a promise that some trajectory is clear. Otherwise you’d use the word “permission” or “approval” or “authorization”, wouldn’t you? The common usage of “clearance” as a synonym for those things has developed as a consequence of the marine and aviation usage.
Peter wrote:
What I was getting at is around post #14 i.e. the ICAO position on VFR in Class D which should apparently be freely given.Of course the radar controller can see you so in reality it is not an issue, but one needs to somehow formalise that position.
In relation to US practice, the tower controller could ask you to remain clear of the Delta Airspace on initial contact if he felt that (1) he was too busy to talk to you and (2) he thinks you might have too much conflict with other traffic if he establishes communication and you continue on your way into the Class D before he can deal with your transit or landing request. This happens relatively rarely.
Peter wrote:
The IFR traffic is supposed to separate itself from VFR traffic (if in VMC) but in reality they are probably busy as hell and not looking out of the window.
bookworm wrote:
In class D, VFR traffic is not separated from anything else. So a clearance doesn’t make sense.
“Separation” doesn’t simply mean “keep apart”, it is a technical term with a very specific meaning — that aircraft are kept apart according to the separation rules. One of the obligations of ATC is to prevent collisions and certainly, VFR clearances in class D can be made so as to prevent collisions, even if the VFR flight is not technically separated from IFR.
Aviathor wrote:
In France as in all EASA countries, you need a clearance to enter and transit through controlled airspace, whether it is class B, C, or D.
Of course class E is also controlled airspace, but VFR flights don’t require clearances.
Peter wrote:
In the USA, is it really possible for one to enter Class D and fly around as one wishes laterally?
Yes, but since you must remain in radio contact with the control tower as long as you are inside the lateral and vertical bounds of the class D and if the CT provides the pilot with an instruction, it must be obeyed. That is not a clearance. One may be instructed, however, to remain clear of the class D.
Airborne_Again wrote:
“Separation” doesn’t simply mean “keep apart”, it is a technical term with a very specific meaning — that aircraft are kept apart according to the separation rules.
Indeed it is. Separation is a pretty binary thing. Either you’re separated or you’re not. In class D, VFR traffic is not separated, technically, from anything else. Hence the word “clearance” makes no sense to me. That doesn’t prevent instructions being issued.
bookworm wrote:
Yes. That’s the original context for the use of the word “clearance”. It’s a promise that some trajectory is clear. Otherwise you’d use the word “permission” or “approval” or “authorization”, wouldn’t you?
Maybe in English language that is “clear” (ho ho). The Norwegian word meaning the same thing (klarering) imply no such thing as the trajectory is clear, even though it has the same stub clear – klar. It simply means the process of obtaining and making a permission is “klarert” (cleared). Meaning all eventual obstacles (bureaucratic mainly) that would prevent, or could eventually prevent. an action to be done, or a permission to be obtained, is cleared from the process. It is originally used in a bureaucratic/economical sense in old German and Norse, and really has nothing to do with navigation at all. The meaning is not the same as permission, or an approval or an authorization. A clearance doesn’t necessarily involve a permission or approval, and certainly not an authorization, but merely acceptance of action, as in “no objections”.
Maybe different meaning/understanding of the word “clearance” makes problems here? I don’t know, but IMO if someone does not object to a request or a stated course of action, this is pretty much the same as explicitly “give a clearance”.
You don’t see separation as being relevant to removing “obstacles” in a very physical sense?
It’s often worth turning to ICAO when having such a discussion. From Doc 4444:
Air traffic control clearance.
Authorization for an aircraft to proceed under conditions specified by an air traffic control unit.
Note 1.— For convenience, the term “air traffic control clearance” is frequently abbreviated to “clearance” when used in appropriate contexts.
Note 2.— The abbreviated term “clearance” may be prefixed by the words “taxi”, “take-off”, “departure”, “en-route”, “approach” or “landing” to indicate the par- ticular portion of flight to which the air traffic control clearance relates.
So, it seems to me that when operating within Class D, a pilot is required to comply with the terms/conditions of the clearance. Those terms may well be aimed at expediting flow or providing some form of safety buffer (ie not Separation). I’m not sure two-way-comms, operating with impunity until instructed, is quite within the intent of ICAO.
