Finally someone has cottoned on to the operation of transponders.
As 320/20 pointed out, there is enough evidence to show pilots forget to switch to alt. or the transponder is faulty. I can back this up 100%. Even our professional IFR's forget more than one would think.
At the critical locations (AS, LT, HB), operation of transponders by the local GA's is probably even more unpredictable. They've never had to bother too much about transponders, and they've never had to worry about transponder serviceability. ATC at those locations don't have the ability to remind pilots of transponder problems. So TCAS is useless in those situations.
The last line of defence is to expect the VFR's to be monitoring the "appropriate frequency" and to respond when they think they are in conflict with other traffic. I find this just as fanciful as expecting them to know where all the holding patterns are, and to be able to avoid them.
And MoFo, there are plenty of reasons why transponders are not operated by VFR pilots. Some of these reasons, believe it or not, are because
1. They think big brother is watching them, and
2. They do not wish to be pinged for some illegal operations.
These are the sad facts.
CG