Transponders

Robert Ehrlich wrote:
An experiment in the french Alps made with a group of tow planes
mimicking glider flight, i.e. circling together from time to time has
shown that transponders, except in mode S, may not be very useful in
gliders. As soon as 2 or more gliders are close together, e.g. circling
in the same thermal of working together the same ridge, they are hit
simultaneaously by the radar beam and generate simultaneaously their
responses, which results in both interfering and nothing useful
received at ATC. I had the chance of having one of the engineers
involved in the experiment as a passenger last September and he confirmed
this. In mode S, as each transponder is specifically adressable,
this mess will probably not occur, a new experiment using them is
planned.

This study is sometimes cited as an excuse to put off installation of
transponders until inexpensive mode S transponders are available. My
take on it is that it addressed a fairly narrow concern, the possible
inability of ATC to properly discern a group of thermalling mode C
equipped gliders. It did not examine whether airborne collision
avoidance systems would continue to provide warnings when confronted by
such situations.

The times when I've been surprised by the close approach of larger
aircraft have been while cruising between thermals, when I'm generally
alone or at a fair distance from other gliders. While thermalling, I
have a view of pretty much the entire sky, and I have a much better
chance of seeing approaching traffic in plenty of time to avoid it.

Marc

Marc Ramsey wrote:
Robert Ehrlich wrote:

An experiment in the french Alps made with a group of tow planes
mimicking glider flight, i.e. circling together from time to time has
shown that transponders, except in mode S, may not be very useful in
gliders. As soon as 2 or more gliders are close together, e.g. circling
in the same thermal of working together the same ridge, they are hit
simultaneaously by the radar beam and generate simultaneaously their
responses, which results in both interfering and nothing useful
received at ATC. I had the chance of having one of the engineers
involved in the experiment as a passenger last September and he confirmed
this. In mode S, as each transponder is specifically adressable,
this mess will probably not occur, a new experiment using them is
planned.


This study is sometimes cited as an excuse to put off installation of
transponders until inexpensive mode S transponders are available. My
take on it is that it addressed a fairly narrow concern, the possible
inability of ATC to properly discern a group of thermalling mode C
equipped gliders. It did not examine whether airborne collision
avoidance systems would continue to provide warnings when confronted by
such situations.

Surely this situation occurs at Minden regularly. Does Reno ATC have
trouble "losing" gliders when they thermal together? Or are they still
aware that something is located there, even if Mode C info is lost? And
even if it is a problem, doesn't ATC still much prefer gliders to have a
transponder than not?

I'd expect at least ONE good signal to be received every 5-15 seconds,
as the gliders' positions change and one antenna is in a much better
position the other ones.

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Eric Greenwell
Washington State
USA

Marc Ramsey wrote:

... It did not examine whether airborne collision
avoidance systems would continue to provide warnings when confronted by
such situations.
...

The only such system I have heard about is TCAS. As far as I know
this system is not available on gliders, only on big airplanes
carrying passengers or military ones. It should emit hints to the
pilot for avoiding the collision based on altitude information, assuming
that the other aircraft is going to fly at a constant altitude, or
to follow the hint of its own TCAS, and neither is true for a glider.

Robert Ehrlich wrote:
The only such system I have heard about is TCAS. As far as I know
this system is not available on gliders, only on big airplanes
carrying passengers or military ones. It should emit hints to the
pilot for avoiding the collision based on altitude information, assuming
that the other aircraft is going to fly at a constant altitude, or
to follow the hint of its own TCAS, and neither is true for a glider.

TCAS/ACAS detects nearby transponder equipped aircraft. In the US and
western Europe, almost all aircraft larger than small twins now have
them. They will provide useful warning of the presence of a nearby mode
C equipped glider, whether or not the glider is flying straight and level.

Marc

....
whether or not the glider is flying straight and level.

No.

Besides, exactly how many gliders are flying with Mode C right now?
Maybe one 1-26 in North Dakota?

F1y1n wrote:
....

whether or not the glider is flying straight and level.


No.

Besides, exactly how many gliders are flying with Mode C right now?
Maybe one 1-26 in North Dakota?

In the USA, hundreds, at least, but mostly in the southwest and eastern
parts of the country. Stick your nose into the cockpits at Minden, for
starters. Once the Microair and Becker became available, they were
flying off the shelves at Wings & Wheels, Knauff & Grove, and elsewhere.
Motorgliders are much more likely to have them, also. In our ASH 26 E
owners group, I think about half of the 30 owners have Mode C.

By the time the 1-26 in North Dakota has one, the rest of us will have
moved onto Mode S.

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Eric Greenwell
Washington State
USA

On Fri, 23 Jan 2004 19:32:14 GMT, Marc Ramsey
wrote:

Robert Ehrlich wrote:
The only such system I have heard about is TCAS. As far as I know
this system is not available on gliders, only on big airplanes
carrying passengers or military ones. It should emit hints to the
pilot for avoiding the collision based on altitude information, assuming
that the other aircraft is going to fly at a constant altitude, or
to follow the hint of its own TCAS, and neither is true for a glider.

TCAS/ACAS detects nearby transponder equipped aircraft. In the US and
western Europe, almost all aircraft larger than small twins now have
them. They will provide useful warning of the presence of a nearby mode
C equipped glider, whether or not the glider is flying straight and level.

Marc


go to www.arinc.com and search for TCAS. You will find a very useful
paper describing the characteristics of the TCAS system.

After describing how wonderful it all is note the sudden disclaimer at
the end.

Mike Borgelt

Mike Borgelt wrote:


go to www.arinc.com and search for TCAS. You will find a very useful
paper describing the characteristics of the TCAS system.

After describing how wonderful it all is note the sudden disclaimer at
the end.

Could you be more specific, like a title? I get 32 hits and the few I
checked don't seem to be it.

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Eric Greenwell
Washington State
USA

On Sat, 24 Jan 2004 14:57:28 -0800, Eric Greenwell
wrote:

Mike Borgelt wrote:


go to www.arinc.com and search for TCAS. You will find a very useful
paper describing the characteristics of the TCAS system.

After describing how wonderful it all is note the sudden disclaimer at
the end.

Could you be more specific, like a title? I get 32 hits and the few I
checked don't seem to be it.


Eric,

The file you want is tcas.pdf
It is about 500k. If you can't find it I'll send it to you.

Mike Borgelt

Mike Borgelt wrote:
On Sat, 24 Jan 2004 14:57:28 -0800, Eric Greenwell
wrote:


Mike Borgelt wrote:


go to www.arinc.com and search for TCAS. You will find a very useful
paper describing the characteristics of the TCAS system.

After describing how wonderful it all is note the sudden disclaimer at
the end.

Could you be more specific, like a title? I get 32 hits and the few I
checked don't seem to be it.



Eric,

The file you want is tcas.pdf
It is about 500k. If you can't find it I'll send it to you.

Please send it - I can't find it. Thanks.
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Eric Greenwell
Washington State
USA