Q: Why clip the zone so closely when Luton are invariably obliging in Zone transits?
A: Because I'm a tosser
Q: Why not at least listen out on Luton Radar's frequency so that you can be aware of any aircraft likely to conflict?
A: Because I'm a tosser
Q: Why be at around 1,700' on an extremely turbulent day when you could be transitting at a much smoother 2,400'?
A: Because I'm a tosser.
I had something very similiar and it scared the hell out of me. I dont fly without a PCAS or TCAS as a result, but of course even that will not detect all traffic.
However, as to the questions you pose I couldnt resist a comment or two.
1. I agree Luton rarely fail to give a transit, but they may not have been so obliging to this twin or they may have asked him to hold (which I have known them to do on occasions). He may have had some other good reason why going around the edge was quicker (as you know transits are usually overhead and a route via Hemel or Pirton may not have been beneficial). So for any number of reasons he may have chosen to skirt the zone. If he had been refused a transit the trouble is we are all tempted to skirt the zone even though such honeypot tactics inherently increase the risk of a collision,
2. Inexcusable in my view!
3. 210 are very stable aircraft. You may have thought it choppy, but there is a good chance he wouldnt have even noticed in a 210.
The chances of a close encounter with fast traffic is hugely increased. Just look at how much less time you have to spot the traffic. Exactly the same happened to me except I was also in a fast twin.
IMO if everyone was pottering around at 80 knots or so see and avoid would have half a chance but the traffic is moving quicker these days and there is more of it (or at least there are more bottle necks, or a bit of both).
Personally I wouldnt rely on see and avoid or on other pilots to spot you (after all most pilots in my experience have a dreadful scan any way) and nor would I rely on their displaying good airmanship. I think it is worth investing in one of these portable CASs - the cost is not very great, and at least almost all fast traffic will be transponding (unless they are completely nuts!).