I think the short answer is that the collision risk is only at low levels, say below 1500ft, but
- many of these people are nontransponding (can't or deliberately won't)
- in the circuit, any form of TCAS is not as useful as it could be anyway
If one flies just a bit higher than the UK GA average, the traffic density is very low and it gets very hard to justify the cost of the fitted system (above £10k) and the portable gadgets are messy because for legal reasons they have to appear to be temporary (removable) installations.
Last edited by IO540; 15th February 2009 at 18:47.