Graeme Cant wrote:
I've heard no reason whatsoever why a GPS in a lunchbox is any different
from a sealed barograph. Of course it would be possible. So I'm
puzzled why it doesn't happen. My guess is it's as much to do with
WHO's telling me it can't be done as it is to WHY.

You are focused on imagined draconian security requirements (which are
actually rather minimal for badge-only flight recorders), and glossing
over the major objection.

A sealed barograph records pressure altitude that can be corrected
according to a calibration chart. This is the standard by which glider
altitude performances have been measured from nearly the beginning. A
COTS in or out of a sealed lunchbox either measures GPS-derived
geometric altitude, or if it has a pressure sensor, a mode-dependent
form of altitude which can not be corrected to pressure altitude using
standard calibration techniques.

My is opinion is (and has been for years) that the IGC should switch
over to using geometric altitude, which would allow use of GPS-derived
altitude with appropriate error bars. But, my opinion is not that of
the majority of members of the IGC, or even GFAC, at this point.

Marc