I favour the mandatory introduction of ModeS and TCAS on all aircraft including Gliders, Micros and Balloons.
Its a mature system, idiot proof and it works very well in practice. The box of electronics now need be no more than a packet of fags in size and the display could be one taken out of a high street PDA or multimedia mobile phone for about £60.
The key is certification. Its the authorities that cause these advances to be so expensive. Yet the cost of accidents is very high by any measure. The CAA should fund a low cost, quick and smart certification of a GA wide TCAS system.
Anything without it would still be allowed to fly but only in an ATZ or under a RIS. Very few aircraft would be without it.
Hundreds and thousands of times a day airliners at 9,000ft are being spuriously vectored around and held high/low because of someone chugging around with their ModeA in a C152. I regularly get "avoiding action - turn right, right heading 180, unknown traffic no height information 3 miles in your 1 o' clock"...
Suddenly 50odd tons of airliner is cranking round a steep (for us) turn with people falling over in the cabin and two pilots scrunching their faces up expecting a loud bang. Although we actually know full well its someone bimbling along at 1,500ft along Weston Super Mare front having a nice day out.
Cheers
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