As the title says really. OCAS with a traffic service and VFR I hadnt previously encountered the expectation to stay relatively tightly at a declared altitude.
From a controller’s perspective it will be pretty hard to provide useful traffic information if you are flying an unpredictable course, whether that is horizontally or vertically. I keep them informed of level changes out of courtesy – request if Traffic service, notify if Basic service. Not sure if request is a requirement under a TS, but no one has yet complained.
AIUI, on a Traffic Service you need to speak the the controller about level changes. Whether this has to be phrased as a “request” I don’t know, but I doubt it because you are OCAS so no clearance can be requested anyway.
When under a traffic service, I always advise the controller of any significant altitude change (“G-xxxx, climbing altitude 3,000 feet”, for which the typical response is “roger” or “no known traffic to affect”, unless it is one of these military types around a MATZ, which sometimes reply “approved”).
I also tell them if I plan to do anything they would not expect from me, such as starting to orbit somewhere, or performing stalls
Controllers build up a mental picture of what is going on, and rely on that when providing their service. While they systematically scan their screens, they won’t spot everything. So all this helps them to maintain their “situational awareness”.
Prompting the comment relating to airspace with an upper limit of 2,500 feet, where I have found that variations of altitude of a few hundred feet have not been cause for concern. In fact any “conflicting traffic” tends to be called anyway, with “traffic, left to right indicating 1,500 feet”, with you at perhaps 2,400 feet. In fact with a range of only 2,000, given no traffic below 500 feet, everything gets called so the relevance of small altitude excursions seems puzzling. With 5, 6 or 7 feet of possible levels then it seems a great deal more relevant. On the occasion in question to be fair the controller did offer a “block” altitude, but it wasnt something I had come across before. I have barrel rolled along a track under a traffic service before , without a block altitude, with thte controller commenting that “you look like you are enjoying yourself”.
Yes, it’s a requirement of a traffic service that you advise the controller of any altitude changes. You don’t need a clearance, just need to let them know what you’re doing.
There is no such requirement on a basic service.
That’s a little known “rule” – just as how so many pilots don’t even know the difference between a TS, a BS, a DS, and a PS.
Unless previously advised, I’ve been changing altitudes freely under a TS and squawking ALT and never had any issues.
(Sorry to bore the non-UK pilots here but I think you get an idea of how miserably complex and poorly understood FIS is applied here!)
Purely out of interest I wonder if someone has a reference?
I had a quick look at MATS Part 1 which explains that under a traffic service the terms of reference are for the controller to call traffic within 3,000 feet and 3nm with the obvious caveat that it may be less (or more) depending on “controller work load and radar performance”. The service is of course available IFR or VFR. I cant see any specific reference to VFR remaining at a declared altitude, and in the scenario I mentioned any traffic from SFC to the base should be called anyway so it is not as if the controller should be using an assigned height to filter traffic calls. It just doesnt feel right, expecially as I have had more traffic services than hot lunches (well not quite) and never before been expected to remain at an altitude where the operational parameters are only 2,000 feet.
As Cobalt indicated it is often a godd idea, and I dont dispute that for a moment, but good ideas are not the same as requirements.
The case in point was on a bumpy convective day recently and I couldnt be bothered to remain at an exact altitude as it was more enjoyable riding with the thermals. I guess the block was no more than 400 feet, between 1,800 and 2,200 with the base at 2,500.
I hasten to add it is not that I mind at all, and the controllers do a great job, it was just an unusual “mention”.
This is the closest that I can find.
On page 3 it says
Traffic Service
ATC will expect you to fly in accordance with the details you have passed them. You should not change from this, or from any agreed heading or level/level block, without first advising ATC AND obtaining a response from them; they may be coordinating your flight against other aircraft, based on their ability to predict where you’re going.
Admittedly it sounds like if you don’t pass them your altitude in your initial call, then you’re not bound to inform them. But then your altitude is supposed to be part of your “Pass your message” call.
Bp – thank you.
I am not sure these components are part of your initial call, or necessarily could be. For example I have just departed XYZ and call for a traffic service in the climb which will often be granted with ATC often not especially interested in the precise route, turning points or altitude. How often in fact are we asked or give a heading when OCAS? Of course if AT request the information it is given, but rarely is that my experience. It is just my guess that most controllers will give traffic within a sensible “bubble” around the aircraft without being overly concerned about heading or altitude, more especially given that some of the traffic maybe mode A anyway.
