Interesting thing with transponders

On Mar 5, 10:04*pm, Hagbard Celine wrote:
" No "havoc" is created by two transponders sqawking 1200 near each
other."

Tell that to the Dutch who fly in the Schiphol area...

Shiphol had a problem with the back-end processing and display of Mode
S derived traffic data on their display screens. In hindsight this
seems an awfully obvious thing they missed with Mode S transponder
mandates.

Some summary to the problem is at

http://eurocontrol.int/msa/public/st...Procedure.html

Transponders provide visibility for gliders to both ATC and airliner/
fast jets TCAS and are therefore a critical item anywhere we are
mixing those types of aircraft. And I fail to see how a particular
display capacity/planning problem at Shiphol is that relevant to any
general idea of carriage of transponders.

Darryl

On Mar 5, 3:57*pm, JS wrote:
Forgive me. Most of my flying is in MOAs, so I treat it all as such.
* This briefing was for flights in the R-2508 Complex, the collection
of Restricted and Military airspace surrounding Edwards Air Force Base
and China Lake Naval Air Station. It makes up a good percentage of the
southern California task area, regularly used by gliders from Nevada
and California. The complex extends from surface to unlimited.
* Thinking of the alternative, I don't mind hearing ATC warning
someone that there's a glider maneuvering at their altitude, 12:00, 5
miles. Had assumed that other than current draw there wasn't a down
side to a certified transponder installation, but an alarm going off
at ATC for no apparent reason is something to be aware of.
Your mileage may vary.
Jim
* If you're unfamiliar with the R2508 Complex, and care to have a
look...http://www.edwards.af.mil/r-2508.asp

Jim

I'm still completely missing the point of your post.

If two gliders are squakwing 1200 they will set of a relatively low-
intensity traffic warning. The controllers should be used to this
happening a lot with GA and (for your area) glider traffic. If both
aircraft are squawking 1200 the controllers likely can't even talk to
the pilots involved. Is anybody suggesting they would rather not have
transponders that enable them to "see" gliders and therefore be able
to route military traffic around them?

If either aircraft is squawking something other than 1200 then it is
on a flight plan or flight following and the controller should want to
know about the alert. If they don't I'd really like to know why.

If a glider contacts approach and requests flight following or similar
and they are flying in formation or close to other gliders it is
common sense for them to alert the controller there are other gliders
in the close proximity (whether they are transponder equipped or not).
You should talk to the controllers about the procedures they want you
to use in those circumstances.

If you are in close truly close formation (which might happen in some
buddy flying) ATC may prefer you to deactivate the transponder on all
but one aircraft in the formation. This helps avoid false alerts and
avoids the Mode-C synchronous garbing issue that Eric alluded to. The
procedure is described in the AIM. This is not something that glider
flights, even buddy fights, would normally do. But again if there are
false alert issues with your local control facility talk to them about
when, if ever, they would want you to use this.

Darryl

On Mar 6, 11:47 am, Darryl Ramm wrote:
If you are in close truly close formation (which might happen in some
buddy flying) ATC may prefer you to deactivate the transponder on all
but one aircraft in the formation.

Correct, that is what was suggested by ATC... Especially if a glider
has been issued a discrete code. If the glider is on the discrete code
during tow, turn the transponder in the towplane to Standby until the
glider releases. All but one glider in the thermal or group flight
turns their transponder to SBY.
(Think of what these standby transponders do for PCAS use.)

The point of my initial post is that there is a lot more to using a
transponder in an aircraft that is routinely maneuvered close to other
aircraft than first meets the eye!
And keep looking out the window.
Jim

On Mar 6, 4:32*pm, JS wrote:
On Mar 6, 11:47 am, Darryl Ramm wrote:

If you are in close truly close formation (which might happen in some
buddy flying) ATC may prefer you to deactivate the transponder on all
but one aircraft in the formation.

* Correct, that is what was suggested by ATC... Especially if a glider
has been issued a discrete code. If the glider is on the discrete code
during tow, turn the transponder in the towplane to Standby until the
glider releases. All but one glider in the thermal or group flight
turns their transponder to SBY.
(Think of what these standby transponders do for PCAS use.)

Jim

Sorry but I'm not following the last part of the comment either about
"standby transponders" or at least I am not follwoing if you are
thinking this is a problem or not. Once off tow both transponders
would be on and the PCAS system should operate normally. While on tow
a PCAS unit like the Zaon MRX in the glider squawking standby might
think the towplane's transponder is its own and supress the tow plane
as a threat. I'd argue that is not a problem and actually what you
want--you want the PCAS to suppress the alert and while on tow you
know where the tow plane is (I hope!). And that allows any other
threats coming close to be warned about. Experience from people who
fly with a PCAS in their glider without a transponder (or transponder
in standby) with a tow plane with a transponder would be interesting.

I think it is absolutely the wrong advice to say that gliders should
be turning off and on their transponders without coordinating this
with ATC. That seriously cannot be what ATC wants? For example in
discussions of this with Reno approach, they want this only for close
formation flights (i.e not typical glider flights) and only when those
flights have contacted Reno approach and advised that it is a flight
of multiple aircraft with leader squawking.

The advice to turn off transponders when in thermals just seems
impractical and dangerous, let alone a violation of FARs. You want
people to do this if the other gliders are squawking 1200 or if they
are assigned a discrete code? How do you know they are on a discrete
code or not? Who decides who turns off a transponder and who turn one
on and when. Is this radio chatter going to happen over the approach
frequency?

If a tow plane contacts approach for flight following then they need
to let approach know it is a tow/formation flight with glider
squawking standby--so the controller is not surprised when the glider
pops up on his radar.

Pilots also should not be trying to docuble-guess the decorrelation
capability of TCAS interrogators. i.e. Even with just Mode-C equipped
threats a TCAS equipped aircraft can see multiple aircraft even if
their signals overlap a fair amount. You don't want to be thinking you
are turning off your tranpodner might be helping ATC and then make you
invisible to TCAS that could otherwise "see" you. Especially since
TCAS-II issues vertical resolution advisories there is a risk a TCAS-
II could issue an RA that would fly the aircraft straight into you as
it tries to avoid a gilder in the thermal that is above or below you
with its transponder on. (I'm not talking about the case of a thermal
stacked with many tens of gliders with Mode-C transponders, there have
been some studies of the problem of transponder synchronous garbling
in those cases). BTW if any of those gliders have a Mode-S transponder
like the Trig TT-21 then this avoids the Mode-C synchronous garbling
issues and TCAS and ATC are capable of unambiguously seeing a
relatively large number of individual threats in the same proximity.

Bottom line. I would hope people turn on the transponder and leave it
on unless they are using flight following for a formation/tow flight
and if so then talk to the local ATC facility about how they want to
handle the radio procedures. I know there are battery concerns, but
turning off for long periods to save battery power is different (but
also a violation of FARs), and I'd hope with modern transponders this
is really a not a requirement.


Darryl

On Mar 6, 6:31*am, brian whatcott wrote:
BT wrote:

* /snip/
* "Transport" military aircraft may or may not have TCAS, it depends on
* their vintage, and they do not have an air to air radar to "ping" a
* transponder.
* " Heavy Bomber" military aircraft may not have TCAS, it depends on their
* vintage, and they do not have an air to air radar to "ping" a
transponder.
* /snip/

* BT "retired military aviator" and one time ATC controller.

I know the C-5 has TCAS. It uses squitter mode and interrogates
transponders.
The KC-135 has TCAS. I am almost certain it too interrogates.
* (I should know this, but I did not update the transponder model for
the KC-135 simulators, and cannot recall. Military aircraft are subject
to continuous performance updates.)

Brian W

All USAF C5 an KC-10 have TCAS-II/ETCAS (military variant). I
occasionally get to share airspace with KC-10s out of Travis AFB and
glad they have TCAS-II and I have a transponder (and I'm usually on
flight following with Travis approach if close to Travis).

I believe all KC-135s got TCAS-II/ETCAS in the Pacer/CRAG upgrade
program starting back last decade. Maybe some initially got only TCAS-
I.

C-130s have TCAS. And so on. I think the general assumption today
should be that military transport aircraft have TCAS-II. Outside
tactical exercises I expect those TCAS systems to be operating. When
operating normally all these system will interrogate mode C and S
transponders independent of ground radar or other interrogators.

Darryl

bildan wrote:
On Mar 6, 8:01 am, "Wayne Paul" wrote:

I find the assertion that military aircraft do not have transponders humorous. Wasn't it the military that developed the system back in WWII?
"Transport" military aircraft may or may not have TCAS, it depends on
their vintage, and they do not have an air to air radar to "ping" a
transponder.
" Heavy Bomber" military aircraft may not have TCAS, it depends on their
vintage, and they do not have an air to air radar to "ping" a

transponder.

BT "retired military aviator" and one time ATC controller.

I know the C-5 has TCAS. It uses squitter mode and interrogates
transponders.
The KC-135 has TCAS. I am almost certain it too interrogates.
(I should know this, but I did not update the transponder model for
the KC-135 simulators, and cannot recall. Military aircraft are subject
to continuous performance updates.)

Brian W


You're lucky. I was on the heavy cruiser USS St. Paul watching when
the missile cruiser USS Canberra blasted an AD5 Skyraider out of the
sky with a missile because of an inoperative transponder. The 4-man
A5 crew was lost.

Back to the basic transponder discussion.

It's obvious the US air traffic control system is based on a military
command structure. All information is kicked up the chain of command
for a decision while the ops people at the bottom wait for an answer.
The oxymoron "Military Intelligence" applies.
That's not the case in eastern Washington State, which has a lot of C17s
running around. The tower at Grant County informs them of potential
conflicts in their area, though nowadays, most/all have TCAS and aren't
dependent on the tower for timely information.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

I must have been hallucinating during the briefing at Joshua approach.
Time to give up.
Jim

On Mar 5, 9:41*pm, "BT" wrote:
As Jim said... but not entirely accurate. And a response by another
responder, not entirely accurate.

"Most" fighter type aircraft can interrogate Mode 3 transponders on their
air to air search radars and get a return.
"Most" fighter type aircraft do not have TCAS. Modern Aircraft might.
"Transport" military aircraft may or may not have TCAS, it depends on their
vintage, and they do not have an air to air radar to "ping" a transponder..
" Heavy Bomber" military aircraft may not have TCAS, it depends on their
vintage, and they do not have an air to air radar to "ping" a transponder..

If a flight of 4 fighters (or more than one) is transitioning airspace
outside of a MOA, ATC will have the wingmen, "Strangle the parrot", so
everyone will only see one transponder return, not four and the ATC radar
will not "go crazy with alerts".

BT "retired military aviator" and one time ATC controller.

Well, yes. A-10s, T-38s, T-45s don't have radars so can't interrogate
(although the latter two may have TCAS - I would hope they do!).
Early F-16s and F-18s didn't have interrogators, but all the later
versions do, as do all F-15s, etc. While fighters do not have TCAS,
I think a lot of trainers do, for obvious operational safety reasons.

Plus, there is Link 16, which lets each fighter in a flight see what
the rest is seeing, and what AWACS is seeing - another way to detect
other aircraft.

But that is just gravy - the important point here is that military
aircraft operating in joint use airspace WILL have a transponder on -
so flight following should work - talk to center if you are going
through a MOA that is hot!! - and if all else fails and you see a
problem developing in a MOA between gliders and military aircraft -
call on Guard (121.5) and they will likely hear you - beats a midair
anyday and you get to talk to your tax money at work, literally.

Kirk
"retired military aviator" and one time interrogator of civilian
transponder traffic in MOAs from the pit of his F-4 (and that was 30
years ago!)

On Mar 7, 10:57*am, JS wrote:
I must have been hallucinating during the briefing at Joshua approach.
Time to give up.
Jim

Jim, I'd be really interested to hear what what is being said in the
Joshua approach briefing. It could be a misunderstanding, or an
actual lack of knowledge between agencies and users on each other's
capabilities - not the first time that has happened.

Has there been a reciprocal briefing of glider operations and
capabilities to Center and AF personnel?

I know when I've worked with the AF on similar issues in the Luke area
(coordinating for regional contest, which would be transiting hot MOAs
during the week), there were often misconceptions (!!) that had to be
cleared up, on both sides.

Cheers,

Kirk
66

On Mar 6, 8:46*pm, Darryl Ramm wrote:
On Mar 6, 4:32*pm, JS wrote:

On Mar 6, 11:47 am, Darryl Ramm wrote:

If you are in close truly close formation (which might happen in some
buddy flying) ATC may prefer you to deactivate the transponder on all
but one aircraft in the formation.

* Correct, that is what was suggested by ATC... Especially if a glider
has been issued a discrete code. If the glider is on the discrete code
during tow, turn the transponder in the towplane to Standby until the
glider releases. All but one glider in the thermal or group flight
turns their transponder to SBY.
(Think of what these standby transponders do for PCAS use.)

Jim

Sorry but I'm not following the last part of the comment either about
"standby transponders" or at least I am not follwoing if you are
thinking this is a problem or not. Once off tow both transponders
would be on and the PCAS system should operate normally. While on tow
a PCAS unit like theZaonMRXin the glider squawking standby might
think the towplane's transponder is its own and supress the tow plane
as a threat. I'd argue that is not a *problem and actually what you
want--you want the PCAS to suppress the alert and while on tow you
know where the tow plane is (I hope!). And that allows any other
threats coming close to be warned about. Experience from people who
fly with a PCAS in their glider without a transponder (or transponder
in standby) with a tow plane with a transponder would be interesting.

I think it is absolutely the wrong advice to say that gliders should
be turning off and on their transponders without coordinating this
with ATC. That seriously cannot be what ATC wants? For example in
discussions of this with Reno approach, they want this only for close
formation flights (i.e not typical glider flights) and only when those
flights have contacted Reno approach and advised that it is a flight
of multiple aircraft with leader squawking.

The advice to turn off transponders when in thermals just seems
impractical and dangerous, let alone a violation of FARs. You want
people to do this if the other gliders are squawking 1200 or if they
are assigned a discrete code? How do you know they are on a discrete
code or not? Who decides who turns off a transponder and who turn one
on and when. Is this radio chatter going to happen over the approach
frequency?

If a tow plane contacts approach for flight following then they need
to let approach know it is a tow/formation flight with glider
squawking standby--so the controller is not surprised when the glider
pops up on his radar.

Pilots also should not be trying to docuble-guess the decorrelation
capability of TCAS interrogators. i.e. Even with just Mode-C equipped
threats a TCAS equipped aircraft can see multiple aircraft even if
their signals overlap a fair amount. You don't want to be thinking you
are turning off your tranpodner might be helping ATC and then make you
invisible to TCAS that could otherwise "see" you. Especially since
TCAS-II issues vertical resolution advisories there is a risk a TCAS-
II could issue an RA that would fly the aircraft straight into you as
it tries to avoid a gilder in the thermal that is above or below you
with its transponder on. (I'm not talking about the case of a thermal
stacked with many tens of gliders with Mode-C transponders, there have
been some studies of the problem of transponder synchronous garbling
in those cases). BTW if any of those gliders have a Mode-S transponder
like the Trig TT-21 then this avoids the Mode-C synchronous garbling
issues and TCAS and ATC are capable of unambiguously seeing a
relatively large number of individual threats in the same proximity.

Bottom line. I would hope people turn on the transponder and leave it
on unless they are using flight following for a formation/tow flight
and if so then talk to the local ATC facility about how they want to
handle the radio procedures. I know there are battery concerns, but
turning off for long periods to save battery power is different (but
also a violation of FARs), and I'd hope with modern transponders this
is really a not a requirement.

Darryl

I have been only loosly following this thread. I'm pretty confused at
this point, but now have specific questions.

We have a ZAON PCAS in our club glider. We are now installing a
transponder too. I understand that the PCAS will know that the
glider's own transponder is not a threat so it will filter it out.

If we tow behind a towplane which also has a transponder, what will
happen? Will the PCAS see the tow plane as a threat, and display
that? But another airplane might be on a collision course... but
the PCAS will not see that because it sees the towplane as the closest
threat?

OR..........will the PCAS think that the towplane transponder is
actually the glider's transponder since it stays at the same relative
altitiude and position? Will it filter out both the glider's
transponder and the tow planes' transponder?

Should we put the glider's transponder to "stand by" during tow? If
we do, will the PCAS then think the tow plane's transponder is really
the glider's transponder and filter it out, allowing the PCAS to see
other targets?

Should we just say "screw it" and ignore the PCAS entirely during tow?

Cookie