Transponderz

In equipment I fly (MD11 with TCAS II) I get azimuth and distance (estimated) with no altitude info. If I'm in Class A airspace, I don't worry about it a lot. Down low, I start looking.

On Friday, November 2, 2012 2:44:34 PM UTC-5, Eric Greenwell wrote:
On 11/2/2012 9:33 AM, Dave Nadler wrote:

- Mode S will not cause a bunch of gliders in a thermal

to become invisible to a TCAS-equipped approaching jet,

as can happen with Mode A/C,



Even though the TCAS function doesn't work, is the approaching jet made

aware there are transponders at that 2-D position, altitude unknown?



What happens when the jet approaches a Mode A equipped aircraft? Is the

pilot made aware of it, even though the TCAS system cannot give him

climb/dive command?



--

Eric Greenwell - Washington State, USA (change ".netto" to ".us" to

email me)

For heavens sake Eric, please read the link.
Pay attention to "fruiting" and "multiple transponders
all transmitting at almost the same time, creating
noise like everybody talking at the same time,
unreadable by ATC or TCAS".

You know, kinda like RAS.

For this reason:
- aircraft in formation only have ONE aircraft's
transponder turned on
- aircraft approaching Oshkosh are required to turn
their transponders OFF (except Mode S)
- the rest of the world has effectively outlawed
Mode A/C in favor of Mode S.

Hope that's clear,
Best Regards, Dave

On Nov 2, 5:55*pm, Dave Nadler wrote:
For heavens sake Eric, please read the link.
Pay attention to "fruiting" and "multiple transponders
all transmitting at almost the same time, creating
noise like everybody talking at the same time,
unreadable by ATC or TCAS".

You know, kinda like RAS.

For this reason:
- aircraft in formation only have ONE aircraft's
* transponder turned on
- aircraft approaching Oshkosh are required to turn
* their transponders OFF (except Mode S)
- the rest of the world has effectively outlawed
* Mode A/C in favor of Mode S.

Hope that's clear,
Best Regards, Dave

Dave,

I am wondering if using Oshkosh as an example applicable to a few
sailplanes, in a thermal, is not a bit of a strawman argument.

A separate point, it is my impression that traffic is so congested
there that the controllers are overwhelmed, not that the signals are
garbled and unreadable.

Mode S is superior being less of a load on our current system, but
still, Mode C is valid, safe and not the worthless tired technology
that it seems to be portrayed as.

Kind regards,

Mike

A few gliders in a thermal is not the Oshkosh scenario, where
controllers are overloaded with traffic and transponders are asked to
be turned off.

On Friday, November 2, 2012 1:06:28 PM UTC-7, wrote:
In equipment I fly (MD11 with TCAS II) I get azimuth and distance (estimated) with no altitude info. If I'm in Class A airspace, I don't worry about it a lot. Down low, I start looking.

What do you mean by "no altitude info". A TCAS II display is required to encode relative altitude information as a part of the traffic symbol "threat level" choice. And I think its required to have the relative altitude display numbers above/below the symbols. What system/version is in the MD-11?

And since "I get..." is ambiguous as to whether you mean you see on a display or whether the TCAS II system sees relative altitude. TCAS systems do see altitudes of all the nearby aircraft. Or they need to, if its a Mode C rich environment and they suffer from data collisions where the Mode C replies are not readable then the TCAS system quickly becomes useless for those threats (can't issue TA or RA and you may not see any azimuth). The good news is the quadrant antennas and hardware signal decorrelators (that can essentially untangle overlapping transponder transmissions) that TCAS II uses helps reduce problems with Mode-C garbling.

And to answer Eric's question, TCAS I and II would not see mode-A only transponders. They only issue Mode-C interrogations (well they do more for Mode S magic stuff but that does not change the discussion). Not interrogating Mode A helps cut down on wasting bandwidth/garbling and avoid possible Mode C/Mode A code aliasing problems. Anyhow nobody flies Mode-A only transponders anymore.

The bottom line for practical use is if you have Mode C transponder today there is nothing "wrong" with it, keep using it if you fly where transponders should be used. If you are purchasing a new transponder it makes no sense to purchase a Mode C unit today when there are great Mode S transponders available from folks like Trig.

But for ADS-B data-out futures... just don't hold your breath on the FAA making ADS-B data-out easy to install/affordable any time soon, even if you have a Trig transponder.

And if you fly near airliners and fast jets, from a technology viewpoint its not Flarm or ADS-B-data-in or even ADS-B data-out you want, its a Mode C or Mode S transponder that is seen by ATC radar and TCAS I and II. Know local traffic procedures, have your head on a swivel, and talk to ATC where possible/appropriate.

Darryl

On 11/2/2012 4:55 PM, Dave Nadler wrote:

For heavens sake Eric, please read the link.
Pay attention to "fruiting" and "multiple transponders
all transmitting at almost the same time, creating
noise like everybody talking at the same time,
unreadable by ATC or TCAS".

You know, kinda like RAS.

For this reason:
- aircraft in formation only have ONE aircraft's
transponder turned on
- aircraft approaching Oshkosh are required to turn
their transponders OFF (except Mode S)
- the rest of the world has effectively outlawed
Mode A/C in favor of Mode S.

Hope that's clear,
Best Regards, Dave

Here's what the link says in #14: "A gaggle with multiple Mode C
transponders active may be invisible to TCAS collision avoidance,
because TCAS must receive ungarbled Mode C altitude replies to function."

It's not clear to me from that sentence that the gliders will be
completely invisible to the TCAS _system_, only that it's collision
avoidance functions won't work. Does the approaching, TCAS equipped
aircraft get _any_ indication there are aircraft with transponders in
that situation?

I understand TCAS will work much better if there is Mode C transponders
have some separation from each other. I'm just finding it hard to
understand that a TCAS system will be completely unaware of a bunch of
transponders, even if they are close together.

Does ATC see anything out there, even if the TCAS system can not?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz

On Friday, November 2, 2012 8:39:32 PM UTC-7, Eric Greenwell wrote:
On 11/2/2012 4:55 PM, Dave Nadler wrote:



For heavens sake Eric, please read the link.

Pay attention to "fruiting" and "multiple transponders

all transmitting at almost the same time, creating

noise like everybody talking at the same time,

unreadable by ATC or TCAS".



You know, kinda like RAS.



For this reason:

- aircraft in formation only have ONE aircraft's

transponder turned on

- aircraft approaching Oshkosh are required to turn

their transponders OFF (except Mode S)

- the rest of the world has effectively outlawed

Mode A/C in favor of Mode S.



Hope that's clear,

Best Regards, Dave



Here's what the link says in #14: "A gaggle with multiple Mode C

transponders active may be invisible to TCAS collision avoidance,

because TCAS must receive ungarbled Mode C altitude replies to function."



It's not clear to me from that sentence that the gliders will be

completely invisible to the TCAS _system_, only that it's collision

avoidance functions won't work. Does the approaching, TCAS equipped

aircraft get _any_ indication there are aircraft with transponders in

that situation?



I understand TCAS will work much better if there is Mode C transponders

have some separation from each other. I'm just finding it hard to

understand that a TCAS system will be completely unaware of a bunch of

transponders, even if they are close together.



Does ATC see anything out there, even if the TCAS system can not?


The danger here is this is not written for a technical audience and is confusing on multiple levels.

Firstly you can have several Mode-C equipped gliders in a gaggle or otherwise close by and the TCAS may well decode the transponders and see them as individual targets with valid direction, range and altitude data. As I mentioned with the decorrelators (or called "degarblers") and other tricks TCAS can handle some degree of garbling.

The mention of "TCAS collision avoidance" is likely meaning the RA (resolution advisory) capability of TCAS II, and if you have any threat that the Mode-C altitude replies really are not being clearly read then the RA part of TCAS II can not/will not function at all.

The TCAS may display a threat direction/range even of the altitude information is being garbled but there is no simple guarantee in garbled environment of what exactly will happen, it may or may not display all the aircraft with or without altitude data or (hopefully rarely) with incorrect altitude. But what matters really is the TA and RA and you really need the Mode C replies decoded properly for that. I expect TCAS I to be very useful against Mode C equipped gliders in usual buddy flying or small gaggles. Fly an airliner straight into a large (vertically spaced) gaggle of gliders and I have zero expectations that it will have a clue what to do with an RA, and that RA may well fly the airliner into a collision. OTOH I expect the gaggle to also be visible on the TCAS display -- not that I ever want to rely on the pilots looking a that display. An airliner going into a huge gaggle of Mode-S equipped gliders may also not fare well and TCAS may compute an unsafe RA (since RAs are based on altitude actions only and it can't/won't steer you around the gaggle). I'd hope ATC has noticed any very large gaggles and the gliders are in touch with ATC. So at some extent I find some of this worrying about what happens with large gaggles with Mode-C kind of unnecessary.

I hope ATC would be well aware there is say a large gaggle of gliders in a location (one benefit of a dedicated glider transponder code), be able to route traffic around that gaggle. And I'd hope that ATC would be savvy enough to suspect they may have very poor target acquisition, altitude reporting and garbling problems. And hopefully a large gaggle will show up even on primary radar in many locations. And I'd expect them to be upset if a large gargle is parked near where they usually want to route traffic. But hope is not always a good thing, go talk to your local ATC guys, radar techs are usually pretty friendly if you want to have a detailed talk with them.

You can always just ask your local ATC guys what they prefer if gliders are buddy flying etc. Most places I've asked (e.g. Reno approach in pre NORCAL days -- I dont' know about now) never felt they needed push for it but were happy to work with gliders buddy flying etc. where one or more of them wanted to go squawk standby.

Again the message is get a transponder if you fly near airliners and fast jets, lots of GA traffic etc. There is absolutely no need to replace a Mode C transponder, they work fine but if buying a new transponder it make no sense to get a Mode C when more modern Mode S transponders are available.

Darryl

On Friday, November 2, 2012 10:17:18 PM UTC-6, Darryl Ramm wrote:
On Friday, November 2, 2012 8:39:32 PM UTC-7, Eric Greenwell wrote:

On 11/2/2012 4:55 PM, Dave Nadler wrote:







For heavens sake Eric, please read the link.



Pay attention to "fruiting" and "multiple transponders



all transmitting at almost the same time, creating



noise like everybody talking at the same time,



unreadable by ATC or TCAS".







You know, kinda like RAS.







For this reason:



- aircraft in formation only have ONE aircraft's



transponder turned on



- aircraft approaching Oshkosh are required to turn



their transponders OFF (except Mode S)



- the rest of the world has effectively outlawed



Mode A/C in favor of Mode S.







Hope that's clear,



Best Regards, Dave







Here's what the link says in #14: "A gaggle with multiple Mode C



transponders active may be invisible to TCAS collision avoidance,



because TCAS must receive ungarbled Mode C altitude replies to function.."







It's not clear to me from that sentence that the gliders will be



completely invisible to the TCAS _system_, only that it's collision



avoidance functions won't work. Does the approaching, TCAS equipped



aircraft get _any_ indication there are aircraft with transponders in



that situation?







I understand TCAS will work much better if there is Mode C transponders



have some separation from each other. I'm just finding it hard to



understand that a TCAS system will be completely unaware of a bunch of



transponders, even if they are close together.







Does ATC see anything out there, even if the TCAS system can not?





The danger here is this is not written for a technical audience and is confusing on multiple levels.



Firstly you can have several Mode-C equipped gliders in a gaggle or otherwise close by and the TCAS may well decode the transponders and see them as individual targets with valid direction, range and altitude data. As I mentioned with the decorrelators (or called "degarblers") and other tricks TCAS can handle some degree of garbling.



The mention of "TCAS collision avoidance" is likely meaning the RA (resolution advisory) capability of TCAS II, and if you have any threat that the Mode-C altitude replies really are not being clearly read then the RA part of TCAS II can not/will not function at all.



The TCAS may display a threat direction/range even of the altitude information is being garbled but there is no simple guarantee in garbled environment of what exactly will happen, it may or may not display all the aircraft with or without altitude data or (hopefully rarely) with incorrect altitude. But what matters really is the TA and RA and you really need the Mode C replies decoded properly for that. I expect TCAS I to be very useful against Mode C equipped gliders in usual buddy flying or small gaggles. Fly an airliner straight into a large (vertically spaced) gaggle of gliders and I have zero expectations that it will have a clue what to do with an RA, and that RA may well fly the airliner into a collision. OTOH I expect the gaggle to also be visible on the TCAS display -- not that I ever want to rely on the pilots looking a that display. An airliner going into a huge gaggle of Mode-S equipped gliders may also not fare well and TCAS may compute an unsafe RA (since RAs are based on altitude actions only and it can't/won't steer you around the gaggle). I'd hope ATC has noticed any very large gaggles and the gliders are in touch with ATC. So at some extent I find some of this worrying about what happens with large gaggles with Mode-C kind of unnecessary.



I hope ATC would be well aware there is say a large gaggle of gliders in a location (one benefit of a dedicated glider transponder code), be able to route traffic around that gaggle. And I'd hope that ATC would be savvy enough to suspect they may have very poor target acquisition, altitude reporting and garbling problems. And hopefully a large gaggle will show up even on primary radar in many locations. And I'd expect them to be upset if a large gargle is parked near where they usually want to route traffic. But hope is not always a good thing, go talk to your local ATC guys, radar techs are usually pretty friendly if you want to have a detailed talk with them.



You can always just ask your local ATC guys what they prefer if gliders are buddy flying etc. Most places I've asked (e.g. Reno approach in pre NORCAL days -- I dont' know about now) never felt they needed push for it but were happy to work with gliders buddy flying etc. where one or more of them wanted to go squawk standby.
Thanks Darryl. Appreciate the effort.

Mike




Again the message is get a transponder if you fly near airliners and fast jets, lots of GA traffic etc. There is absolutely no need to replace a Mode C transponder, they work fine but if buying a new transponder it make no sense to get a Mode C when more modern Mode S transponders are available.



Darryl

On Friday, November 2, 2012 8:45:43 PM UTC-4, Mike C wrote:
I am wondering if using Oshkosh as an example applicable to a few
sailplanes, in a thermal, is not a bit of a strawman argument.

Oshkosh was used as an example of where Mode A/C cannot work.

A separate point, it is my impression that traffic is so congested
there that the controllers are overwhelmed, not that the signals are
garbled and unreadable.

"Your impression" ? The controllers are not overwhelmed, they use
appropriate tools and manage the highest traffic density anywhere,
very professionally. As you would know if you've flown into
Oshkosh (or in the airshow ;-)

Mode C is valid, safe and not the worthless tired technology
that it seems to be portrayed as.

Sure, which is why Mode C was phased out in Germany years ago,
with the rest of the world following...

For new installations, get Mode S and we'll all be happier
with the results. And it won't have to be replaced if/when
FAA catches up with the rest of the world (not holding my
breath).

Mode C does work in many cases, but...

On Friday, November 2, 2012 11:17:18 PM UTC-5, Darryl Ramm wrote:
On Friday, November 2, 2012 8:39:32 PM UTC-7, Eric Greenwell wrote:

On 11/2/2012 4:55 PM, Dave Nadler wrote:







For heavens sake Eric, please read the link.



Pay attention to "fruiting" and "multiple transponders



all transmitting at almost the same time, creating



noise like everybody talking at the same time,



unreadable by ATC or TCAS".







You know, kinda like RAS.







For this reason:



- aircraft in formation only have ONE aircraft's



transponder turned on



- aircraft approaching Oshkosh are required to turn



their transponders OFF (except Mode S)



- the rest of the world has effectively outlawed



Mode A/C in favor of Mode S.







Hope that's clear,



Best Regards, Dave







Here's what the link says in #14: "A gaggle with multiple Mode C



transponders active may be invisible to TCAS collision avoidance,



because TCAS must receive ungarbled Mode C altitude replies to function.."







It's not clear to me from that sentence that the gliders will be



completely invisible to the TCAS _system_, only that it's collision



avoidance functions won't work. Does the approaching, TCAS equipped



aircraft get _any_ indication there are aircraft with transponders in



that situation?







I understand TCAS will work much better if there is Mode C transponders



have some separation from each other. I'm just finding it hard to



understand that a TCAS system will be completely unaware of a bunch of



transponders, even if they are close together.







Does ATC see anything out there, even if the TCAS system can not?





The danger here is this is not written for a technical audience and is confusing on multiple levels.



Firstly you can have several Mode-C equipped gliders in a gaggle or otherwise close by and the TCAS may well decode the transponders and see them as individual targets with valid direction, range and altitude data. As I mentioned with the decorrelators (or called "degarblers") and other tricks TCAS can handle some degree of garbling.



The mention of "TCAS collision avoidance" is likely meaning the RA (resolution advisory) capability of TCAS II, and if you have any threat that the Mode-C altitude replies really are not being clearly read then the RA part of TCAS II can not/will not function at all.



The TCAS may display a threat direction/range even of the altitude information is being garbled but there is no simple guarantee in garbled environment of what exactly will happen, it may or may not display all the aircraft with or without altitude data or (hopefully rarely) with incorrect altitude. But what matters really is the TA and RA and you really need the Mode C replies decoded properly for that. I expect TCAS I to be very useful against Mode C equipped gliders in usual buddy flying or small gaggles. Fly an airliner straight into a large (vertically spaced) gaggle of gliders and I have zero expectations that it will have a clue what to do with an RA, and that RA may well fly the airliner into a collision. OTOH I expect the gaggle to also be visible on the TCAS display -- not that I ever want to rely on the pilots looking a that display. An airliner going into a huge gaggle of Mode-S equipped gliders may also not fare well and TCAS may compute an unsafe RA (since RAs are based on altitude actions only and it can't/won't steer you around the gaggle). I'd hope ATC has noticed any very large gaggles and the gliders are in touch with ATC. So at some extent I find some of this worrying about what happens with large gaggles with Mode-C kind of unnecessary.



I hope ATC would be well aware there is say a large gaggle of gliders in a location (one benefit of a dedicated glider transponder code), be able to route traffic around that gaggle. And I'd hope that ATC would be savvy enough to suspect they may have very poor target acquisition, altitude reporting and garbling problems. And hopefully a large gaggle will show up even on primary radar in many locations. And I'd expect them to be upset if a large gargle is parked near where they usually want to route traffic. But hope is not always a good thing, go talk to your local ATC guys, radar techs are usually pretty friendly if you want to have a detailed talk with them.



You can always just ask your local ATC guys what they prefer if gliders are buddy flying etc. Most places I've asked (e.g. Reno approach in pre NORCAL days -- I dont' know about now) never felt they needed push for it but were happy to work with gliders buddy flying etc. where one or more of them wanted to go squawk standby.



Again the message is get a transponder if you fly near airliners and fast jets, lots of GA traffic etc. There is absolutely no need to replace a Mode C transponder, they work fine but if buying a new transponder it make no sense to get a Mode C when more modern Mode S transponders are available.



Darryl

Not directly related to the multiple C-mode transmits discussed here but still pertaining to Darryl's urging to get a transponder: After a season of 1202 (and last year's 1201) dedicated code here in the Chicago area, I have to praise the group that made this happen for us glider guiders. Our club lives under the approach path over Joliet VOR into Midway and the jets are often at around 5,000'. They reliably divert when we start flying in the area without us being in contact with Approach. Going North through the Aurora D airspace, I hear them on the tower frequency point out "glider at 5,200' SW of field" to approaching and departing traffic before I call them to say my intentions. Passing by a very busy sky jump operation to the West of us, they actually called me twice this year on 123.3 because they had gotten a phone or radio call from ATC pointing out a glider target close to their operations. Being identified as a glider without being necessarily in contact with ATC is very helpful. Get a transponder, please!

Herb

On Saturday, November 3, 2012 8:59:11 AM UTC-6, Dave Nadler wrote:
On Friday, November 2, 2012 8:45:43 PM UTC-4, Mike C wrote:

I am wondering if using Oshkosh as an example applicable to a few

sailplanes, in a thermal, is not a bit of a strawman argument.



Oshkosh was used as an example of where Mode A/C cannot work.



A separate point, it is my impression that traffic is so congested

there that the controllers are overwhelmed, not that the signals are

garbled and unreadable.



"Your impression" ? The controllers are not overwhelmed, they use

appropriate tools and manage the highest traffic density anywhere,

very professionally. As you would know if you've flown into

Oshkosh (or in the airshow ;-)



Mode C is valid, safe and not the worthless tired technology

that it seems to be portrayed as.



Sure, which is why Mode C was phased out in Germany years ago,

with the rest of the world following...



For new installations, get Mode S and we'll all be happier

with the results. And it won't have to be replaced if/when

FAA catches up with the rest of the world (not holding my

breath).



Mode C does work in many cases, but...