Another mid-air (UK)

Intelligence aside, we are irritated since the non believers are risking our lives.

Ramy

At 04:39 07 August 2014, Ramy wrote:
Intelligence aside, we are irritated since the non believers are risking
our lives.

Ramy


As a uk pilot let me put some background to this .
It's a comp that is proud of the fact that it can put 50 or 60 sailplanes
in the
air in well under a hour.
I flew there in the similar comp about 12 years ago,and while I completed
the
week I decided that it was outside my comfort zone and have not been back.
I was a very early user of flarm,probably because I lost 2 friends to a mid
air.
Other than including the flarm display in my scan I don't real look at it
unless
I get a bleep .
If I am in a gaggle I reduce my cockpit scan ,because by far the most
important thing is monitoring the rest of the circus plus the joining
gliders
that do not alway arrive at the bottom.,some will try and bounce the
thermal
arriving at mid hight at speed,pulling up and going back on track .
Dangerous you say ,that's comp pilots for you.
Flarm is great for spotting the distant glider before it becomes a problem

,once in a gaggle it's just a distraction.

At 06:40 07 August 2014, Jonathon May wrote:


As a uk pilot let me put some background to this .
It's a comp that is proud of the fact that it can put 50 or 60
sailplanes
in the
air in well under a hour.
I flew there in the similar comp about 12 years ago,and while
I completed
the
week I decided that it was outside my comfort zone and have
not been back.
I was a very early user of flarm,probably because I lost 2
friends to a mid
air.
Other than including the flarm display in my scan I don't real
look at it
unless
I get a bleep .
If I am in a gaggle I reduce my cockpit scan ,because by far
the most
important thing is monitoring the rest of the circus plus the
joining
gliders
that do not alway arrive at the bottom.,some will try and
bounce the
thermal
arriving at mid hight at speed,pulling up and going back on
track .
Dangerous you say ,that's comp pilots for you.
Flarm is great for spotting the distant glider before it becomes
a problem

,once in a gaggle it's just a distraction.


Swiss FLARM have said right from the start that see and avoid
rather than FLARM is the most important safety measure in
concentric gaggles. I support nearly everything that you say
but would like to look more at your last comment about FLARM
being *just* a distraction in gaggles:

Every alert received equals one given. You are confident of
your look out in thermal gaggles so you find receiving FLARM
alerts there a distraction. Fair enough - I don't react
specifically to each individual alert in a busy gaggle either.
But are you just as confident of other pilots' look out - the ones
that you are simultaneously giving the FLARM alerts to? The
ones that may be in your blind spot? Would you prefer that
they get FLARM alerts in gaggles as a wake up call to look out
all around or do you think that they will be so distracted by
them that their see and avoid will be compromised?

I don't think there is a definite right or wrong answer but I very
much prefer to give and receive alerts to keep us all on our toes
and also to help me to fly so as not to give alerts to others.

John Galloway

At 04:37 07 August 2014, Ramy wrote:
Dan, you kidding about the accuracy of GPS, right? Or maybe
trolling? I
realize you may have never used a GPS in gliders, but I am sure
you've seen
GPS in cars which can pin point in which Lane you are traveling.
OK, I am
not going to fall into this trap.

Ramy


Most automotive GPS systems augment the raw GPS signal with a
'Lock to Road' function. If you have a route set they also often
assume you are traveling the route, so assume you will be and
display you in the correct lane.

You can see this in two ways... On my system if I choose to ignore
the guidance and take a different route the GPS shows me
travelling the the suggest route for a few seconds before snapping
to the new road. If you turn off the 'lock to road' function, it will
often show you several (or even tens) of metres from the road.

Using a modern ( and FLARM is not) GPS engine in an optimum
installation, raw GPS is still +-8m at 95% confidence and 16m at
99% confidence (Current US DoD stats)

On Thursday, August 7, 2014 1:30:14 AM UTC-7, Stats Watcher wrote:
At 04:37 07 August 2014, Ramy wrote:

Dan, you kidding about the accuracy of GPS, right? Or maybe

trolling? I

realize you may have never used a GPS in gliders, but I am sure

you've seen

GPS in cars which can pin point in which Lane you are traveling.

OK, I am

not going to fall into this trap.



Ramy





Most automotive GPS systems augment the raw GPS signal with a

'Lock to Road' function. If you have a route set they also often

assume you are traveling the route, so assume you will be and

display you in the correct lane.



You can see this in two ways... On my system if I choose to ignore

the guidance and take a different route the GPS shows me

travelling the the suggest route for a few seconds before snapping

to the new road. If you turn off the 'lock to road' function, it will

often show you several (or even tens) of metres from the road.



Using a modern ( and FLARM is not) GPS engine in an optimum

installation, raw GPS is still +-8m at 95% confidence and 16m at

99% confidence (Current US DoD stats)

Isn't the Flarm GPS WAAS corrected? The WAAS standard of performance is 1.6M nominal horizontal (95%). When the NDGPS system is functional (and GPS engines take advantage of it) this will be reduced to 15 cm.

Even with 8m accuracy, It is more than sufficient for accurate collision avoidance, unless someone considers half a wingspan not accurate enough for collision warning with another glider or obstacle.

Ramy

At 15:04 07 August 2014, jfitch wrote:

Isn't the Flarm GPS WAAS corrected? The WAAS standard of
performance is
1.6M nominal horizontal (95%). When the NDGPS system is
functional (and GPS
engines take advantage of it) this will be reduced to 15 cm.


Not in Europe as WAAS is US only. A search of the Powerflarm
website returned 0 (zero) occurrences of the term 'WAAS'. So it
seems unlikley.... Same result for NDGPS, so that seems unlikely
too.. If someone finds something different I will obviously be wrong
but until that point it's still +-16m (ie a whole wingspan) at 99%
confidence

On Thursday, 7 August 2014 16:49:07 UTC+1, Stats Watcher wrote:
Not in Europe as WAAS is US only. A search of the Powerflarm
website returned 0 (zero) occurrences of the term 'WAAS'. So it
seems unlikley.... Same result for NDGPS, so that seems unlikely
too.. If someone finds something different I will obviously be wrong
but until that point it's still +-16m (ie a whole wingspan) at 99%
confidence

EGNOS is the European equivalent of WAAS.

On Thursday, August 7, 2014 11:46:30 AM UTC-4, Ramy wrote:
Even with 8m accuracy, It is more than sufficient for accurate collision avoidance, unless someone considers half a wingspan not accurate enough for collision warning with another glider or obstacle.

Prompted to comment here by my Geek Fascination Syndrome (GFS)...

I'd guess that the error on each position fix is not significant. Flarm is computing trajectories from multiple position fixes, so a maximum +/- 8M error for each fix will be smoothed out by the statistical distribution of a large number of position fix errors. Some of the errors are + and some are -. Average 100 GPS position fixes and you will get a pretty accurate position.

I'd expect that the sampling rate is high enough to make the trajectory calculations quite accurate. If the sampling rate was not fast enough they could put a faster processor into the units. Plus as Ramy pointed out, FLARM must be alerting for 'possible near misses' because there will be small deviations in trajectory caused by turbulence and pilot control inputs.

The 8M 'error' of GPS is unlikely to be the critical factor that keeps FLARM from fulfilling its mission. I'd bet that the critical factor is the human pilot, that being the most inherently error prone and undependable part of the system.

At 16:06 07 August 2014, son_of_flubber wrote:
On Thursday, August 7, 2014 11:46:30 AM UTC-4, Ramy
wrote:
Even with 8m accuracy, It is more than sufficient for
accurate
collision=
avoidance, unless someone considers half a wingspan not
accurate enough
fo=
r collision warning with another glider or obstacle.=20

Prompted to comment here by my Geek Fascination Syndrome
(GFS)...

I'd guess that the error on each position fix is not significant.
Flarm is
=
computing trajectories from multiple position fixes, so a
maximum +/- 8M
er=
ror for each fix will be smoothed out by the statistical
distribution of a
=
large number of position fix errors. Some of the errors are +
and some are
=
-. Average 100 GPS position fixes and you will get a pretty
accurate
positi=
on.

I'd expect that the sampling rate is high enough to make the
trajectory
cal=
culations quite accurate. If the sampling rate was not fast
enough they
co=
uld put a faster processor into the units. Plus as Ramy pointed
out,
FLARM=
must be alerting for 'possible near misses' because there will
be small
de=
viations in trajectory caused by turbulence and pilot control
inputs.

The 8M 'error' of GPS is unlikely to be the critical factor that
keeps
FLAR=
M from fulfilling its mission. I'd bet that the critical factor is the
hum=
an pilot, that being the most inherently error prone and
undependable part
=
of the system.


+-8m 95% of the time is best case, under ideal conditions and
installations. Do you fly only in ideal conditions and have an
ideal installation? f the answer is 'no' your error will be larger.
Also this is 2D error. As everyone 'knows' and goes on ad-
nauseam, GPS vertical error is significantly worse.

Have you 'any' evidence for the rest of your post or is it just
pure supposition? If you analyse the data rate and bandwidth
requirements of the data link you'll realise what you suggest is
impossible