Interesting thing with transponders

This morning's threads about transponders and collisions prompted...
During the trip to Joshua Approach which Cindy Brickner organised
last week, amongst other things we were presented with what happens at
the Air Traffic Control end when we are sending our location to them
via transponder.
If you are issued a discrete squawk code by ATC, and fly close to
another aircraft with a transponder; turned on and ALT encoding,
discrete or VFR (1200) code; then ATC computers start making noise
about the possible crash. They can only suppress so much of this
before the warnings sound like "something out of Star Wars".
Apparently two aircraft squawking VFR are visually reported as a
conflict but do not have the same level of alert.
Close to another aircraft could be:
On tow behind a transponder-equipped towplane.
Sharing a thermal.
Pair flying.
Not that gliders ever do any of that.
So as we're all moving toward using radios and transponders to keep
separation, be aware of the havoc we may be wreaking at ATC. Not a
good way to make friends! If you're Mode S, they have your
registration too!
As previously suspected, military aircraft do not use transponders,
so they get your position verbally from ATC but your current
transponder-based collision warning systems will do nothing.
Look out the window,
Jim

Hi Jim,

If you are arguing against the use of transponders - I must wholeheartedly
disagree. I think they are the best investment you can make it the safety
of your aircraft, and many of the other aircraft sharing the airspace with
you - including passenger jets.

I suppose I could be accused of being biased because I sell transponders.
But my feelings are sincere. I hope that a lot more gliders will put
transponders in their gliders in the future. Very few gliders in here MN
have them - and my gliderport is located in a notch (cutout) of the Class B
airspace. We see a lot of passenger airline traffic. But they probably
don't see us.

Best Regards,

Paul Remde

"JS" wrote in message
...
This morning's threads about transponders and collisions prompted...
During the trip to Joshua Approach which Cindy Brickner organised
last week, amongst other things we were presented with what happens at
the Air Traffic Control end when we are sending our location to them
via transponder.
If you are issued a discrete squawk code by ATC, and fly close to
another aircraft with a transponder; turned on and ALT encoding,
discrete or VFR (1200) code; then ATC computers start making noise
about the possible crash. They can only suppress so much of this
before the warnings sound like "something out of Star Wars".
Apparently two aircraft squawking VFR are visually reported as a
conflict but do not have the same level of alert.
Close to another aircraft could be:
On tow behind a transponder-equipped towplane.
Sharing a thermal.
Pair flying.
Not that gliders ever do any of that.
So as we're all moving toward using radios and transponders to keep
separation, be aware of the havoc we may be wreaking at ATC. Not a
good way to make friends! If you're Mode S, they have your
registration too!
As previously suspected, military aircraft do not use transponders,
so they get your position verbally from ATC but your current
transponder-based collision warning systems will do nothing.
Look out the window,
Jim

On Mar 5, 2:54*pm, JS wrote:

* As previously suspected, military aircraft do not use transponders,
so they get your position verbally *from ATC but your current
transponder-based collision warning systems will do nothing.
Look out the window,
Jim

What gives you the idea that military planes do not use transponders?
All US (and probably most of the rest of the worlds) military aircraft
have transponders and are required to use them when out of restricted
airspace - mil flights are usually on an IFR flight plan with a
specific assigned Mode 3 squawk until they are in their exercise
airspace and can cancel - and then usually will leave one or modes on
(typically, a USAF jet has modes 1, 2, 3, C, 4, and S).

In addition, fighters can interrogate and detect other transponders
(think super-TCAS), while transports probably all have TCAS or
equivalent - remember, most airspace is not owned by the military, so
we have to share!

Where you can have a problem is with military aircraft on LLTRs - they
may be too low to detect your transponder until too late - so know
where the local LLTRs are and be careful near them. Same for active
MOAs - worth a check with center to find out if a MOA is hot - lots of
Guard and Reserve units train on weekends.

Looking out the window, of course, is always a good thing!

Cheers,

Kirk
66

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

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

If they want us to use transponders.. then they have to put up with the 1200
codes (or discrete glider code) all over their screens.

As Jim said... but not entirely accurate. And a response by another
responder, not entirely accurate.
Yes, if a "discrete" assigned code gets to close to another discrete or 1200
code, alarms go off.
If two 1200 codes get too close, alarms do not necessarily go off, 1200
(VFR) codes implies that the controller does not have the aircraft on the
radio frequency and there is nothing the controller could do about it.

"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.

"JS" wrote in message
...
This morning's threads about transponders and collisions prompted...
During the trip to Joshua Approach which Cindy Brickner organised
last week, amongst other things we were presented with what happens at
the Air Traffic Control end when we are sending our location to them
via transponder.
If you are issued a discrete squawk code by ATC, and fly close to
another aircraft with a transponder; turned on and ALT encoding,
discrete or VFR (1200) code; then ATC computers start making noise
about the possible crash. They can only suppress so much of this
before the warnings sound like "something out of Star Wars".
Apparently two aircraft squawking VFR are visually reported as a
conflict but do not have the same level of alert.
Close to another aircraft could be:
On tow behind a transponder-equipped towplane.
Sharing a thermal.
Pair flying.
Not that gliders ever do any of that.
So as we're all moving toward using radios and transponders to keep
separation, be aware of the havoc we may be wreaking at ATC. Not a
good way to make friends! If you're Mode S, they have your
registration too!
As previously suspected, military aircraft do not use transponders,
so they get your position verbally from ATC but your current
transponder-based collision warning systems will do nothing.
Look out the window,
Jim

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

I find the assertion that military aircraft do not have transponders humorous. Wasn't it the military that developed the system back in WWII? Isn't our current system a direct descendant of the original IFF (http://en.wikipedia.org/wiki/Identif..._friend_or_foe) and still uses to original coding system? ("Squawk 1200, etc.)



BTW, I am alive today because of the refusal to allow the USS Long Beach to blindly fire on an aircraft from which it was not receiving a transponder signal. The aircraft in question turned out to be my A-6A Intruder with an inoperative transponder.





"brian whatcott" wrote in message ...

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