Just wondering how you handle this kind of situation, Approach to Spanish (for example) airport, Class A starts at 983ft AGL but the ground level varies by over 1000 feet on the route (up, down, up, down!), unless ytou have a radar altimeter and continual change level how can you be sure of not infringing the airspace and not hitting the ground?
Can you just take the highest point on the route and base your altitude on this??
Unless I was flying a helicopter, I wouldn't be messing around below the Class A airspace. A Special VFR clearance is your friend.
It's a really good question, which has been asked many times over the years, and nobody I know has ever found a definition.
My take on it is that, in an obviously ambiguous scenario like this, nobody actually cares...
I would take the highest obstacle within say 5-10 nm and add 1000ft to that and take that as the effective CAS base.
CAS is there to protect commercial traffic and there isn't going to be any commercial traffic anywhere near any terrain like that.
But it must to some extent depend on what the CAS is protecting. Is it enroute traffic (in which case the airway MEA will be based on the highest point of that airway segment, plus 1000ft or - if above 5000ft - plus 2000ft) or is it some instrument procedure for an airport (in which case the designer might have laid out a holding pattern into a depression between some peaks)?
Such airspace definitions are rubbish and nobody expects you to be holier than thou. I'd try to sort out something better with FIS/ATC and if not possible, fly at a reasonable altitude say 800ft above the average elevation.
Simple - you fly in controlled airspace. No probs whatsoever. Not every country is as anal as the UK.
Btw - where do you find a Class A in Spain at 983ft agl ????
Not an easy answer I think. If Spain in in accordance with ICAO, then there is no flight below 500ft AGL. If class A starts at 1000ftAGL, then you've only got a 500ft window over rolling terrain.
Personally I wouldn't go there except for very short legs.
A Special VFR clearance is your friend.
A SVFR clearance is only available in a CTR, which means airspace that goes to the ground. So unfortunately it won't be available in the case of an airspace who's base is 1000ft AGL.
Such airspace definitions are rubbish
Very much agree... they are very common however, outside the UK.
A SVFR clearance is only available in a CTR, which means airspace that goes to the ground
Quite right too... another thing is that if you want some unusual clearance in some countries where ATC English language proficiency is Level Minus 4, you probably won't get it.
Thanks for all the suggestions...
Here is a typical example which we will be flying next Monday...
Valencia to Ibiza via VFR entry point 'N' (San antonio) its under Palma Class A (base 1000' AGL)until the Ibiza CTR and the ground level varies enormously !
I was intending to request SVFR prior to the Palma Class A...
Italy also has lots of Class A that is defined by x feet AGL. I seem to remember that, technically, GL it is defined as the highest point within 5 miles.
My advice is to not to become too obsessed with that. Sometimes, the gradients of the terrain are much steeper than the gradient of climb or descent of the average SEP. What is important is to fly safely. Unfortunately, sometimes people forget this whilst trying to stay 100% legal. Not good. In Italy, where you find class A at 1000 feet AGL, often, there will be no IFR traffic whatsoever below, say, 5000 feet AGL. So again, use your good judgement. It is also true however, that sometimes, when flying "too high", ATC/FIS will call you and question your altitude above the ground. So, they do have some basic maps, but certainly, they are not so accurate as to allow them to precisely determine your true altitude above the ground. So, when they say "please confirm you are maintaing max 1000 feet AGL?", just confirm, with a firm voice "yes sir, we are maintaining max 1000 feet AGL".
P.S. SVFR in class A airspace is not available in Italy, and neither in Spain AFAIK.