Transponders in micros
Unfortunately we have a very restrictive micro definition compared with most of Europe and else ware. We have a concept of a max empty weight, which is more rigorous than most of the three axis designs were intended to meet. The result is that many micros (the CT for example) are within 1lb of the max allowed empty weight. If you add more than 1lb of installed weight to such a design it becomes illegal and is reduced to the level of a garden ornament. This is preventing many micro owners from installing transponders. Many of the aircraft in this category are capable of cursing at 120kn and have a r of c in excess of 1200 fpm. Most of the pilots are people who grew up flying PA28’s etc and my experience is they fly at regular GA levels when conditions are appropriate.
Many UK owned gliders have no approved transponder installation. As the manufacturers of many of these machines do not exist it is virtually impossible to install a transponder, even if there is sufficient batt power.
Both of the above issues were brought up at the Mode S meetings, so the CAA/EASA has had lots of time to change things.
When I was researching my collision avoidance article for Flyer we came to the conclusion that about 50% of the things your average PPL are likely to hit are transponder equipped. I would not expect this to have changed greatly since.
Rod1