Gliders and Transponders......again.

There are a number of other issues associated with Mode S Transponders. BTW
they would have to be Mode S in the UK, not Mode A/C. They would also have
to be professionally fitted and tested by a licenced radio engineer, which
is unlikely to be cheap!

1) Would they still work if a glider is in a tightly banked thermal turn,
with the ground plane at a considerable angle, and the glider just moving
with the wind? Don't they (ATC) filter out slow moving objects anyway so
they don't see clouds, flocks of birds, etc.

2) Would a glider climbing rapidly in a thermal or wave towards the base
of an airway or controlled upper airspace (with no intention of entering
it), or flying just below it, generate spurious TCAS alarms that might
unnecessary frighten the jet jockeys into making violent avoidance
manoeuvres and upsetting their passengers?

3) What effect would a whole gaggle of competition gliders have on ground
radar services or TCAS? Indeed the CAA has suggested turning them off in
such circumstances, but then what's the point of having them fitted in
the first place? I understand that Air Traffic Control can selectively
filter out some returns, but again what would happen if they selected the
one that was an actual threat?

Basically I object to having to pay out the best part of £2k to fit
unproven (for gliders) technology to my £8k glider, that will probably be
out of date anyway in a few years time.

I am also unconvinced that an unshielded 120 Watt RF output is not a
health hazard, when even 4 watt microwaves are considered dangerous.

I understand that some of the UAVs will be operated in the Poodle 51st
State (i.e. the UK) by the good ol' USAF, which is another reason to hate
the Yanks, if Iraq and Afghanistan aren't already bad enough!

Derek C

At 16:25 19 January 2009, Darryl Ramm wrote:
On Jan 19, 12:00=A0am, Derek Copeland wrote:
As a UK glider pilot, I would be happy to fit a Mode S transponder to
my
glider if only they where cheap, ran all day on a small battery, gave
ME
some form of collision warning (TCAS?) from other gliders and light
aircraft, and didn't fry my n*ts off with 120 Watt Radio Freqency
being
emitted from an antenna 6 inches behind my unshielded backside.

There is a GPS based collision avoidance system called Flarm which
meets
most of my requirements and could be cheaply fitted to all aircraft
including airliners. Our CAA won't even countenance this, as it is
not
compatable with their existing WW2 technology Radar Systems. The push
to
fly UAVs all over our isle may also come into this.

I should add that in the UK commercial aircraft generally fly in
segregated Class A, B, and D airspace, and gliders in the rest, so
conflicts are exceedingly rare.

Derek Copeland

I really don't want to get into a debate about UK and USA transponder
issues. I think some of the issues facing the UK are different,
including issues with attempts to grab airspace and UK specfic UAVs
issues (we may have some of our own here) etc. However yet again in
this transponder debate people keep raising red herrings or offering
misinformation. I hope the BGA and others in the UK are not using all
these sorts of arguments in their debate, because some of them are
embarrassingly silly and would take away from other valid points.

So lets waste more space on this..

There is no reason to believe that you would get excessive RF exposure
form a properly installed transponder antenna. Most antennas are 1/4
wave stubs or blades that require a ground plane and when mounted
where glider manufactures recommend (on the underbody of the fuselage
near the undercarriage) just won't expose the pilot to significant RF
radiation. If your glider is metal or carbon fibre you have even more
isolation. Also be careful when comparing to other RF sources -- the
power specifications of transponders are the peak pulse power. The
duty cycle is quite low even in an environments with lots of active
TCAS interrogations. I've seen transponder antennas installed between
pilots legs, nearly in contact with he pilot. Darwin has something to
say about that.

As for power requirements there are several choices of transponder
that along with an encoder draw ~0.5 A. This is the sort of power
consumption that if your glider's batteries are absolutely already at
the maximum could usually be met by the addition of a small 7Ah
battery VRLA batttery. Say derating the battery 7Ah spec by 50% (for
operating temps below 20C and the load being above 0.05C) would gives
7 hours of run time. Mode-S transponders like the Becker will work
fine down to 10V (which at a 0.5 A load is lower then the discharge
point voltage used to calculate VRLA battery specs). How long are
typical flying days in the UK? The worse case is going to be long cold
wave flights and they may well need a larger battery or use a more
advanced technology battery. But these devices are already in the "use
small battery" category in my book. And I know installing that
battery (or even better a 12Ah battery if you have space) may be a
pain in the neck and cost some money but it is a tough argument to try
to push onto the traveling public, airline and jet owners etc. If I
was the CAA and having to put up with these arguments. I'd be making
the point by showing actual 7Ah battery sizes to highlight the (small)
problem glider pilots and owners are facing.

It is likely unrealistic to expect airliners and fast jets to use
flarm. Most of these aircraft have sophisticate TCAS systems. I hope
glider pilots are not presuming somebody just installs a flarm into
the airliner cockpit. Any flarm type input would need to be integrated
into the TCAS so it can provide s single traffic display and issue a
single RA. This is unlikely to be a low cost modification and why
should those owners do something to accommodate gliders which could
just "get with the system" and install transponders? Then there may be
technical issues with flarm like effective range (can flarm be
modified to respond to airliner interrogations at tens of km? TCAS can
work over distances like that, giving pilots a head's up of traffic
before a RA is required). While flarm seems a fantastic technology
where it is used (not in the USA) I suspect it is a read herring when
talking about providing airliners and fast jets tools to avoid
collisions with gliders.

As for wanting a Mode-S transponder with "TCAS" display. You can get
this today. In the USA PCAS units like the Zaon MRX are popular and
use very low power and relatively low cost (~$500). They provide an
alert but no RA or direction information. But they are impresssively
effective at highlighting traffic (I've flow with one for three
years). They work fine with Mode-S transponders. Yes I know this may
seem a waste of money if you already have a flarm unit. But back to
where I think the Examiner opinion article was trying to focus and
where I'd argue the higher risk to our aport is -- avoiding a
collison with a airliner or passenger carrying jet -- then the glider
does *not* need PCAS or TCAS type capablities. Letting ATC, and if
that fails, TCAS-II in the jet, deal with the conflict is going to be
highly effective.

Darryl