Warped factor,
Please explain your interpretation of vertical separation and how it is acheived. To make it more interesting, have the permit to fly aircraft operating on a special VFR clearance in 10Km visibility and you attempt to pass an IFR flight 1000ft vertically overhead.
The simple fact is that while c of a aircraft are required to have their altimeter certified and checked on a regular basis, permit aircraft have no such restriction. Thus the CAA makes no assurance that a permit to fly aircraft will be within the required maximum permitted error for a certified aircraft. Yet the CAA allows such aircraft to use that altimeter to judge vertical separation from both other aircraft and vertical airspace boundaries.
Have you ever had a look at what some flexwing microlights use as an altimeter - you would be shocked!
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IO540,
I have seen an example of an altimeter being 500ft in error on an aircraft (sticky). The give away at the start fo the flight was that we were at 40,000ft + the field elevation + 150ft with the QNH set so the owner adjusted the altimeter to read field elevation ignoring the QNH provided by ATC. During the descent the altimeter would not move much unless tapped and when tapped would jump some 300ft at a time and sing back and forth over a 300ft arc. Landing with a little bump ensured that the altimeter indicated a reasonable height again. The pilot simply stated that thre was no requirement for the altimeter to be certified and that was why he could only fly the aircraft VFR by day. He explained it as ground moves away - climbing. ground gets closer descending - what more do you what. It was one of those encounters where you simply walk away shaking you head, glad to be alive!
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Of course add that to the fact that a basic PPL is only expected to keep the aircraft within +/- 150ft of the assigned altitude when in smooth air (greather allowances for rough conditions) and there are lots of reasons why a CTA can be infringed by a pilot attempting to fly 100ft below the base.
The point is that pilots are not the sole reasons for infringements. There is a lack of joined up writing within the CAAs ATS, Certification and Pilot standards departments that could continue to cause infringements even if pilots did their best to keep clear.
Regards,
DFC