Originally Posted by SNS3Guppy
ATC needs me to descend. They ask me to keep my speed up and give my best rate of descent. You're operating near the "edge" of the airspace, and think that means something to me or ATC. I deploy the speed brakes and pull the power to idle. I'm doing 250 knots and descend into you from behind, with a high rate of descent. I'm going faster than you think, descending into you at several thousand feet a minute. Even if the altitude to which I'm cleared is the bottom of the controlled airspace in that area, if you're right on the "edge," and if your altitude isn't quite correct, it doesn't take much error, especially with a closure rate of 250 knots or greater and several thousand feet per minute vertically, to wind up with a collision.
I'm departing. I'm heavy, so I'm not climbing as fast as the controller might like. I get a turn away from other traffic, and continue my climb. You're flying with your transponder off, or perhaps have it on, but elect to do so on the edge of a busy terminal area, thinking that it's a good idea so long as you're on the "edge." During departure, I'm busy getting cleaned up and configured for the enroute climb, and I don't have a really great view of other traffic, especially at our climb speeds which may be closer to 300 knots, even below 10,000 (minimum safe speed allows higher than 250). I may be on a vector, and I may pass in and out of controlled airspace during that climb. The controller may make a mistake. Why put yourself in the position of being in a traffic conflict in the first place; it's not safe for either one of us.
Accepting there are undoubtedly reigonal differences, in Australia (and allegedly the UK, though I can't find a reference), if you are in controlled airspace, a 500ft protective buffer to the base is maintained; AC 2.5.1 Section 8.5 refers. I cite these, only because they are jurisdictions in which I have flown. In these places, you do not fly 'in and out of controlled airspace'. Your SIDs and STARs are predicated upon you being able to achieve certain performance in order to comply, and to maintain the protection of that airspace. You are either inside and get the benefit of 'protection', or outside, and play the way the rest of us have to, controlled classes of airspace are there for the simple reason that high speed, heavy jets generally require such protection. I freely admit I know jack about how the US does it.
Originally Posted by SNS3Guppy
Those who would skirt airspace as closely as they can remind me somewhat of someone who might walk on the highway as close to the edge of the highway as possible. One might technically have stepped into traffic, but what if traffic drifts across the line, slightly? Doing the same thing in flight with altimetry systems that can be off slightly means that the analogy is a little more like walking along the highway blindfolded; you have no way of knowing exactly where the "edge" is. Give it a buffer. Stay on the sidewalk. Don't go near the edge. Playing near the edge is asking for trouble, whether it's performance, or airspace. I've spent much of my career in operations involving flight near the edge of performance, foreign airspace, and close to obstacles and terrain, and I'm paid in some of my employment to do just that. Are you? Then why go there?
Again, I suspect you have a reigonally-biassed view - In many parts of the world, being allowed to play in controlled airspace is unlikely at best; furthermore, in my part of the world the bottom of your controlled, protected areas is remarkably close to the ground - leaving us mere mortals quite a narrow zone in which to fly. When the controlled airspace is 1000ft AGL, and I have little hope of a clearance, you can bet your last dollar I'm going to have my fin right up against the bottom of it. You might equally well ask why the professionals need fly so close to the base, and the wild, uncontrolled chaos that reigns beyond..