Transponder requirement confusion

You must be one of the few that has ever had a tube crap out. You
will surely run out of gas before you run out of tubes.

Having it on also allows all the toy collision avoidance things to see
you.
Like TCADS.

Small price to pay for collision avoidance. Please have it on. It's
not just the rule, it's a great idea!!

Bill Hale


wrote:
Quick (hopefully) question to a confusing part of the FARs. With my new (to
me) solid-state transponder, I'm now willing to power it up for even local VFR
flights. Before, I would only turn on my KT-76 if I needed to (VFR advisories, IFR,
Class B/C operation) since I knew the cavity tube had a finite number of hours before
it died. Now that I read through the transponder requirement carefully, it appears
that that's not allowed. Google groups appear to contain previous usenet arguments
regarding this, but the answer's still not quite clear. In particular:

FAR 91.215(5)(c)
(c) Transponder-on operation. While in the airspace as specified in paragraph (b) of
this section or in all controlled airspace, each person operating an aircraft equipped
with an operable ATC transponder maintained in accordance with ??91.413 of this part
shall operate the transponder, including Mode C equipment if installed, and shall
reply on the appropriate code or as assigned by ATC.

"Controlled" airspace also includes Class E... so if you have one (and it's
within the 2-year test), you *have* to turn it on? ... but you aren't *required* to
have one?

If so, that's a very unclear requirement from most colloquial references on
equipment requirements...

Curious...
-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

john smith wrote:



but a TCAS II equipped aircraft can see you.


Only if you have a Mode-S transponder.


?????

wrote:
: You must be one of the few that has ever had a tube crap out. You
: will surely run out of gas before you run out of tubes.

: Having it on also allows all the toy collision avoidance things to see
: you.
: Like TCADS.

: Small price to pay for collision avoidance. Please have it on. It's
: not just the rule, it's a great idea!!

It's not that the tube craps out in-flight... it's just that repeatedly running the transponder when you do not
"need" it (read: in B.F.E., VFR, local-flights) means that you shorten its useful life when you *DO* need it (flight
following, Class-[ABC], IFR). Any time I actually *GO* anywhere where collision avoidance might be an additional
feature, chances are it's a cross-country flight and I'll have it on for that reason.

As I mentioned, I have personally gone through two tube-based transponders in this manner. My mechanic has
also gone through two that lost transmit power due to a dying cavity tube, as has another pilot friend of mine.
Granted, I'm on the low end of the avionics totem pole (ebay specials mostly)... the fact of the matter is that
replacing the cavity tube has been made cost-prohibitive by the part costing $500 or more.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

In the current atmosphere of fear in the US regarding terrorism I do
not think it would be wise to fly VFR anywhere without Mode C in
operation, regulations or not withstanding.
Being right and being safe are two different things.

wrote in message
...

It's not that the tube craps out in-flight... it's just that repeatedly
running the
transponder when you do not "need" it (read: in B.F.E., VFR,
local-flights)
means that you shorten its useful life when you *DO* need it (flight
following, Class-[ABC], IFR).


What's "B.F.E."?

In article . com,
wrote:

wrote:
john smith wrote:

but a TCAS II equipped aircraft can see you.

Only if you have a Mode-S transponder.

Nope, all they need is mode C.

Actually, they don't even need mode C, now that I think about it.
You get different levels of service depending on what the target has.

If they've got Mode A you'll get an callout.
If they've got Mode C then you'll get an RA (climb / descend)
If they've got Mode S and they've also got TCAS, the two TCAS's
will boogie with each other to coordinate the RA.

So really mode S by itself does nothing for TCAS II unless you've
also got a TCAS as well.

My understanding is that the Mode-S provides the communication
information. Mode C may contain altitude, but there is no distance or
direction information.

wrote:
wrote:
: You must be one of the few that has ever had a tube crap out. You
: will surely run out of gas before you run out of tubes.

: Having it on also allows all the toy collision avoidance things to see
: you.
: Like TCADS.

: Small price to pay for collision avoidance. Please have it on. It's
: not just the rule, it's a great idea!!

It's not that the tube craps out in-flight... it's just that repeatedly running the transponder when you do not
"need" it (read: in B.F.E., VFR, local-flights) means that you shorten its useful life when you *DO* need it (flight
following, Class-[ABC], IFR). Any time I actually *GO* anywhere where collision avoidance might be an additional
feature, chances are it's a cross-country flight and I'll have it on for that reason.

As I mentioned, I have personally gone through two tube-based transponders in this manner. My mechanic has
also gone through two that lost transmit power due to a dying cavity tube, as has another pilot friend of mine.
Granted, I'm on the low end of the avionics totem pole (ebay specials mostly)... the fact of the matter is that
replacing the cavity tube has been made cost-prohibitive by the part costing $500 or more.

-Cory


The cavities are pretty robust, and it takes lots of hours to wear them
out. Perhaps you are buying used transponders that are already close to
end of life of the cavity? If you are concerned about cavity life that
much, then why not bite the bullet and get a modern solid-state slide-in
replacement? A new one costs no more than 3 or 4 used ones, comes with
a warranty, and will last you a good long time. Plus some of them come
with added features like altitude read-out, timers, single push VFR and
such that you'll find handy.

Leaving the transponder off makes you blind to TCAS, TCAD, and all of
the low cost passive anti-collision boxes like the Monroy (granted, they
won't see you if you are not in radar coverage anyway unless an active
TCAS interrogates you).

Also, the tube isn't dissipating any power unless it is replying to an
interrogation, so it doesn't take any life off the tube by keeping the
transponder on when it isn't getting interrogated. If you are in an
area where it is getting interrogated, then you are invisible to
whatever radar or TCAS is interrogating you if you have it off. Please
turn it on unless you are on the ground.

Bum F@#k Egypt. i.e. out in the tules

Jim


"Steven P. McNicoll" wrote in message
k.net...


What's "B.F.E."?

john smith wrote:



My understanding is that the Mode-S provides the communication
information. Mode C may contain altitude, but there is no distance or
direction information.

Mode S doesn't provide any distance or direction info to another TCAS.
Each TCAS figures that stuff out on its own.

john smith wrote:

In article . com,
wrote:


wrote:

john smith wrote:


but a TCAS II equipped aircraft can see you.

Only if you have a Mode-S transponder.

Nope, all they need is mode C.

Actually, they don't even need mode C, now that I think about it.
You get different levels of service depending on what the target has.

If they've got Mode A you'll get an callout.
If they've got Mode C then you'll get an RA (climb / descend)
If they've got Mode S and they've also got TCAS, the two TCAS's
will boogie with each other to coordinate the RA.

So really mode S by itself does nothing for TCAS II unless you've
also got a TCAS as well.


My understanding is that the Mode-S provides the communication
information. Mode C may contain altitude, but there is no distance or
direction information.


That's correct. Mode C only transmits either the squawk code or the
encoded altitude, depending on the specific interrogation. However,
TCAS is an active system that sends an interrogation and listens for the
reply. It uses the time delay between the interrogation it sends and
the reply it recieves back to accurately measure range. Many use an
antenna array and beamforming techniques to determine azimuth as well.
Therefore, it can determine both distance and direction, and of course
it gets the altitude directly from the reply.

The passive TCAD boxes do not transmit interrogations. Instead they
listen for replies to other interrogations and use some signal
processing to glean rough range information from the dispersion and
amplitude of the received pulse. Considering the lack of a hard
measurement, they do a pretty decent job at estimating range. Strike
finders work under a similar principle. In the case of a transponder
reply, the job is easier because the transmit pulse shape and amplitude
are pretty narrowly defined for an in-spec transponder. Most of the
TCAD boxes do not provide azimuth info. The ones that do also use a
phase array of antennas and signal processing to do beamforming to
resolve the azimuth.