At 11:08 16 October 2015, Bruce Hoult wrote:
On Friday, October 16, 2015 at 2:20:18 AM UTC+3, Ramy wrote:
On Thursday, October 15, 2015 at 1:15:18 PM UTC-7, Ian wrote:
On 10/10/2015 12:20, Judy Ruprecht wrote:
=20
7. SC3 Annex C Section 3.4 now allows a PR with pressure sensor (eg
Flarm) to have that pressure sensor ignored & the GPS altitude
used.
=20
This is the most significant change to the Sporting Code, for club=20
pilots, since the invention of GPS. Now it is possible to fly badges,
u=
p=20
to gold level, in any glider equipped with a Flarm. As the GPS
altitude=
=20
can be used instead of the pressure altitude, there is no longer a=20
requirement for that Flarm to have a current calibration certificate
fo=
r=20
the pressure sensor.
=20
As many club pilots have access to club ships equipped with Flarm,
they=
=20
can now arrive at their club on a weekend and go and fly badge
flights=
=20
without first having to get hold of a calibrated FR - which might not
b=
e=20
readily available.
=20
However the applicable country's National Association will have to
do=
=20
their homework to put the necessary approvals in place to use Flarm
as
=
a=20
PR. This has already been done for a number of countries, and there
are=
=20
sample approval documents for Flarm available in German, French
and=20
English, which could easily be adapted by other country's National=20
Associations.
=20
Sensibility is finally catching up with red tape...
=20
Ian
=20
Maybe I am missing something, but if GPS altitude can be used instead
of
=
pressure altitude, how can you verify that the pilot did not bust class
A?
=
The difference between pressure and GPS altitude can be close to 1000
feet
=
near 18K. Same question goes for altitude gain and loss measurements.=20

GPS bounces around, especially in altitude due to not often having
satellit=
es near the zenith. But if you average it over 10 or 15 minutes then it's
v=
ery accurate. if you're not moving.

Of course, gliders don't stay put for 10 or 15 minutes. But if you have a
p=
ressure altimeter then you know how much you went up and down at each GPS
r=
eading, even if the altimeter isn't calibrated or set to QNH. In fact you
u=
se the GPS to continuously calibrate the pressure altimeter. Whatever the
a=
verage difference is between GPS and pressure attitude over the last 15
min=
utes, that's how much you should adjust the pressure altitude reading by.
T=
his compensates for both unknown QNH and unknown altimeter calibration at
t=
he same time.

That gives you accurate physical WGS84 altitude, which is perfect for
task
=
verification purposes of altitude gain or loss.

"Busting Class A" is a different matter as that's based on pressure level
n=
ot actual altitude. For that, you need either a calibrated pressure
altimet=
er (only), or your true altitude from the GPS+uncalibrated altimeter
combo
=
AND the area QNH.

(I don't know whether FLARM combines the GPS and pressure in the way
descri=
bed, but you'd certainly hope so .. it's not rocket science)

I believe that for it's anti-collision function Flarm uses GPS Altitude,
smoothed by pressure altitude. i.e. pressure altitude is used to remove the
'bounces' of GPS altitude. In this way, all Flarm use the same datum. Call
it Flarm Altitude if you wish.

But that is for it's anti-collision function. Not to be confused with what
is in the IGC file.

In the IGC file, Flarm records both Pressure and GPS altitude.

The word calibrated is a bit of a misnomer. What that really means is that
a calibration chart is available.

IF there is a question of airspace infringement, the claim can be frozen
until a new calibration chart can be produced. This should only occur in
rare cases where the margin is small.

The GPS altitude can still be used for other aspects of the claim.