Interesting thing with transponders

Kirk, I was at the same tour that Jim was. The scenario was in
relationship to how a controller sees aircraft on his screen and what
alarms go off when two aircraft are near each other. Here's how I
understood it.

In general, two aircraft squawking 1200 are on VFR, not talking to the
controller, and if they get close to each other, as say a towplane and
glider might, or two gliders in the same thermal or wave might be, no
alarm goes off and the controller won't (and really can't) do anything.
He's not talking to either plane and they might not even be on his
frequency.

However, if a plane is assigned a discrete code, anytime that plane goes
near another plane, including those squawking 1200, an alarm will go off
on the controllers screen about potential collisions. Now, with
gliders, this isn't going to happen all that much. Unless another GA
plane on flight following comes nearby or a glider asks for clearance in
a wave window, I don't think that we end up with discrete squawk codes
all that often. In Cal City, there are two possible wave window
clearance dictates, and with one of them, discrete codes are not
necessarily assigned. However, in the other one, they are, and there is
the possibility that two gliders on discrete clearance codes can (and
may want to) fly near each other. This obviously will drive controllers
nuts, so it may simply be courteous to mention to the controller than
you are going to fly near each other as a flight, and switch your
transponder to standby if the controller agrees. Of course, if you
break away, notify the controller again such that he still knows where
you are.

This has nothing to do with standard VFR 1200 traffic. Nor anything to
do with the special 0440 code used in the Reno area (and which is
specially programmed into the Reno area controller's screens to behave
like a 1200 squawk). In the MOA's around Cal City, in one of the wave
window clearance, all non-1200 traffic is diverted around the window, so
the only potential conflicts are other gliders. In the other, military
traffic may use the same area as the wave window, and the military
planes may or may have the transponder data from gliders with discrete
codes (we didn't really talk about that). But military pilots probably
will end up staying away from the wave window area if they're smart once
the controller mentions that the window is active and there are gliders
in the area.

I think that summed up the brief talk had with the controller supervisor
at Joshua. Maybe someone else who was there can correct me.

Jason Kramb




On 3/7/2010 1:22 PM, kirk.stant wrote:
On Mar 7, 10:57 am, 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

Jason,

Thanks for the explanation; that all makes sense. It would seem that
if the discrete code becomes a problem in a wave window, then a common
code (like the Reno 0440 code) would be one way for ATC to handle it -
that would still give TCAS protection for airliners, bizjets, etc.

It looks like there was some confusion about military aircraft
transponder use - bottom line: in common use (civilian and military)
airspace, military aircraft are handled just like civilian aircraft
with transponders - if IFR they are talking to center and get normal
IFR handling, if VFR (say in a MOA running low altitude intercepts)
then they are like other VFR traffic with transponders (and many with
TCAS and interrogators): They may not be talking to center (they will
be on their own freq) so having a TPAS in a glider will definitely
help, and a transponder in the glider may help the military aircraft
detect and avoid the glider.

Good conversation, all in all, IMHO.

Cheers,

KIrk
66