Chris Nicholas wrote:
Tim, thanks. By your silence on the subject, I presume you agree with
my first point: that moving map software using (I think) only GPS
altitude data is apt to mislead pilots into thinking they are below
(or above, depending on QNH on the day) CAS which is defined by flight
levels.

I was short cutting a bit when I said “may”, in “If CAS is defined by
height or altitude, GPS may suffice”. What I was hinting was that at
low levels (e.g. Stansted UK CTA at 1500’), and when QNH and ascents
are close to standard atmosphere, you would be unlikely to be a few
hundred feet wrong.

In principle, yes – FAI requires baro. So does the law in the UK. So
our moving map warning, re height, are undependable.


Chris N.

I am not sure why you seem to be referring to this issue as in the
moving map software or why you seem to assume all "loggers" only pass
GPS based altitudes.

All popular PDA/PNA software that I am aware of is capable of (and
flight computers that support airspace all) will work with pressure
altitude. You want this to all work as it should with "moving map
software" then buy a flight computer/flight recorder etc. that outputs
pressure altitude data over NMEA. Pilots who do not have that better get
the need to defer to their altimeter. As for use for determining
airspace violations post-flight I think this is such a pain in the neck
that pressure recording should always be required (so we likely agree on
that).

I really think the whole position recorder idea from the IGC was
unnecessary and results in yet more confusion. And that is on top of the
already multiple levels of approvals for IGC flight recorders, often
separate ENL options, confusing IGC/FAI rules, different OLC rules,
crappy support for popular legacy products (e.g. Cambridge), ... all
that just ads up to a much worse end-user experience than it should be.

Darryl