I agree that technology is making the issue of transponder carriage easier.
But gliders would have difficulty in powering a tx for a 4 hour flight, microlights, similar. Add to that the Mode A equipped C172s/PA28s etc or those where the transponder output is weak and given the numbers of these aircraft which may total around 10,000 of the 20-odd-k GA craft expecting transponder-equipped aircraft to alert you on your PCAS is playing Russian Roulette.
So you PCAS-equipped owners, don't whinge at people disappearing under your wings without warning - you can expect over 50% of traffic not to alert your expensive PCAS/TCAS. You can even hit squawking traffic.
That happened to me a few weeks back in the Elstree 'circuit'. A PA28R routing from Stapleford towards Wycombe came straight at me. Although I was squawking Mode C and had right of way, he never made the slightest attempt to change course, Sitting there in bovine mode he didn't even notice my flashing my lights or my diving out of his way.
Being on Elstree's frequency I was positioning for arrival at Elstree. He was clipping the ATZ and probably on Farnborough North's frequency (or listening to his iPod).
Having a PCAS or squawking perhaps can give a false sense of security.
So for your own (and our) safety, please look out the window from time to time.....
