Transponder problems with ATC COMS - Video

I was passenger on a $100 hamburger run.

http://www.youtube.com/watch?v=eBl3rbiwpTA

Note, pilot is fresh on getting her VFR ticket and wanted to get some
ground ops experience so she asked me to come along. She also thought
it would be cool to capture her comms with ATC so I brought the
recorder along. Little did we know how much "communicating" was in
her future!

Transponder acted silly on departure and video includes both ATC and
in cockpit communications.

Note, pilot is part owner of the C172 and I was totally clueless on
the operation of her transponder. She just knew how to push the button
to the squawk code. Durn thing is so automated it automatically goes
to mode C on take off. My transponder is nothing as techie as what
was installed in her plane.

While she was flying the plane in the troubleshooting stage, I had
pushed the standby button and saw no display indication that would
show the transponder NOT sending the Mode C data. It still displayed
the FL data. I would have expected that to disappear when I set it to
standby or some indication that Mode C was shut off.

Rather then troubleshoot in an area that was congested with ATC
traffic and cause more chaos with an incorrectly reporting
transponder, we figured to recycle to see if it would clear it up.
Since it didn't clear it up, we canceled the flight following and
turned off the transponder since we had cleared KJAN airspace.

Reason for shutting it off was I was afraid we would be seen as
"unverified traffic" by center at 700 foot higher then what we really
were. Whether these decisions were "procedurally correct" or not I
don't know, but the safe outcome of the flight shows the success of
the flight.

I had asked the pilot what would she have done had she been by
herself, and she said she would have returned back to Madison which in
my eyes is as equally a good decision as mine to cancel flight
following.

I felt the pilot was incredibly composed considering the extra tasks
tossed back at her.

Certain things training sure never covers, and this would be one of
them....

For those interested http://www.youtube.com/watch?v=ru6p-5dP5D0 was
when I was her second passenger just three months ago. As you can
see, she has come a long way on handling an airplane.

You do not mention the make and model of the transponder and I did not see
it in the video. The newer garmin (and others) transponders (if tied to a
GPS) will automatically switch from STBY to ALT when a set ground speed is
reached and return to STBY when it is slowed below that ground speed. It is
possible to turn off ModeC and just squawk the code. It is very unusual for
the altitude to miss report.

BT


"A Lieberma" wrote in message
...
I was passenger on a $100 hamburger run.

http://www.youtube.com/watch?v=eBl3rbiwpTA

Note, pilot is fresh on getting her VFR ticket and wanted to get some
ground ops experience so she asked me to come along. She also thought
it would be cool to capture her comms with ATC so I brought the
recorder along. Little did we know how much "communicating" was in
her future!

Transponder acted silly on departure and video includes both ATC and
in cockpit communications.

Note, pilot is part owner of the C172 and I was totally clueless on
the operation of her transponder. She just knew how to push the button
to the squawk code. Durn thing is so automated it automatically goes
to mode C on take off. My transponder is nothing as techie as what
was installed in her plane.

While she was flying the plane in the troubleshooting stage, I had
pushed the standby button and saw no display indication that would
show the transponder NOT sending the Mode C data. It still displayed
the FL data. I would have expected that to disappear when I set it to
standby or some indication that Mode C was shut off.

Rather then troubleshoot in an area that was congested with ATC
traffic and cause more chaos with an incorrectly reporting
transponder, we figured to recycle to see if it would clear it up.
Since it didn't clear it up, we canceled the flight following and
turned off the transponder since we had cleared KJAN airspace.

Reason for shutting it off was I was afraid we would be seen as
"unverified traffic" by center at 700 foot higher then what we really
were. Whether these decisions were "procedurally correct" or not I
don't know, but the safe outcome of the flight shows the success of
the flight.

I had asked the pilot what would she have done had she been by
herself, and she said she would have returned back to Madison which in
my eyes is as equally a good decision as mine to cancel flight
following.

I felt the pilot was incredibly composed considering the extra tasks
tossed back at her.

Certain things training sure never covers, and this would be one of
them....

For those interested http://www.youtube.com/watch?v=ru6p-5dP5D0 was
when I was her second passenger just three months ago. As you can
see, she has come a long way on handling an airplane.

On Nov 24, 7:38*pm, "BT" wrote:
You do not mention the make and model of the transponder and I did not see
it in the video. The newer garmin (and others) transponders (if tied to a
GPS) will automatically switch from STBY to ALT when a set ground speed is
reached and return to STBY when it is slowed below that ground speed. It is
possible to turn off ModeC and just squawk the code. It is very unusual for
the altitude to miss report.

BT,

I don't remember the make and model myself, it was digital in that it
was LCD looking screen rather then LED (green background)

Googling the Garmin transponder product, buttons look the same, just
don't know the model.

Plane had a Garmin 430 but I don't think it was tied into the GPS.

What you describe going from STBY to ALT worked as advertised and that
was a first for me. The display showed FL 4100 which I took to be the
reported mode C as that is what KJAN said. It was 700 foot off the
altimeter reading. Altimeter was spot on when we verified ASOS
altimeter to field elevation.

What got me was I couldn't and didn't know what the standby buttoon
was (or was not) doing since it didn't indicate no mode C, just
continued to show the FL value.

I assume STBY would stop the altitude reads???

On Nov 24, 5:38*pm, "BT" wrote:
You do not mention the make and model of the transponder and I did not see
it in the video. The newer garmin (and others) transponders (if tied to a
GPS) will automatically switch from STBY to ALT when a set ground speed is
reached and return to STBY when it is slowed below that ground speed. It is
possible to turn off ModeC and just squawk the code. It is very unusual for
the altitude to miss report.


My guess is that its a new C-172 with the G1000 with the transponder
just built in. There is a button along the bottom of the PFD that
brings up transponder options. The transponder is no longer a separate
unit.

-Robert

On Nov 24, 7:54*pm, "Robert M. Gary" wrote:

My guess is that its a new C-172 with the G1000 with the transponder
just built in. There is a button along the bottom of the PFD that
brings up transponder options. The transponder is no longer a separate
unit.

-Robert

Robert,

One thing I can say, it wasn't the G1000

I put in my reply to BT it was a Garmin product looking at pics on
Google.

I hope instructors learn from this to take the time to teach how to
stop the mode C. In my training, I never got such training. My
transponder on my plane is the king analogue flaver, just off, stby,
alt and test and turn knobs to squawk.

Nothing to think about on my transponder but when you start getting
digitalized with more options, maybe some basic transponder 101 with
explanations on why you do what should be in order for flight
training???

On Nov 24, 8:35*pm, Clark wrote:

I just put a 327 in my aircraft - thanks for posting this 'cause it gave me
an excuse to re-read the manual to verify that "On" is Mode A. I'll check
it tomorrow for some visual feedback that Mode A is active vice Mode C.

If you could post your findings, this will be helpful for me for the
next time I fly in that plane, even as a passenger. I hope that I
don't have to use this new found knowledge on a transponder that was
"just fixed" but one just never knows.

For something as benign as a transponder, when it hiccups, it can add
workload to "flying the plane" :-)

I have flown with a couple of Garmin 327's and now have two 330's. The
pressure altitude readout on the transponder comes (as I recall) from the
blind encoder. It is obviously not connected to the altimeter setting.

So, the encoder could be culprit for the mis reported altitude. I suppose
there could be a difference in altitudes of 700 feet if the day was very
non-standard (such as very cold, high pressure, etc).

On Nov 24, 9:15*pm, "Viperdoc" wrote:

So, the encoder could be culprit for the mis reported altitude. I suppose
there could be a difference in altitudes of 700 feet if the day was very
non-standard (such as very cold, high pressure, etc).

30.32 is "higher then normal" for the deep south of MS but I sure hope
that wouldn't have caused that much discrepancy :-)

Since the altimeter was spot on to field elevation at before take off
checklist, I knew that wasn't the culprit.

I suppose if I understand the digital world, that the FL displayed on
the transponder should match field elevation when on the ground. Is
that something worthy of checking before take off to make sure they
match?

"Clark" wrote in message
...
A Lieberma wrote in news:58728052-dba6-4fb3-8e25-
:

On Nov 24, 7:38 pm, "BT" wrote:
You do not mention the make and model of the transponder and I did not
se
e
it in the video. The newer garmin (and others) transponders (if tied to
a
GPS) will automatically switch from STBY to ALT when a set ground speed
i
s
reached and return to STBY when it is slowed below that ground speed. It
is
possible to turn off ModeC and just squawk the code. It is very unusual
f
or
the altitude to miss report.

BT,

I don't remember the make and model myself, it was digital in that it
was LCD looking screen rather then LED (green background)

Googling the Garmin transponder product, buttons look the same, just
don't know the model.

Plane had a Garmin 430 but I don't think it was tied into the GPS.

What you describe going from STBY to ALT worked as advertised and that
was a first for me. The display showed FL 4100 which I took to be the
reported mode C as that is what KJAN said. It was 700 foot off the
altimeter reading. Altimeter was spot on when we verified ASOS
altimeter to field elevation.

What got me was I couldn't and didn't know what the standby buttoon
was (or was not) doing since it didn't indicate no mode C, just
continued to show the FL value.

I assume STBY would stop the altitude reads???

STBY should stop all transponder response on the Garmins. Just pressing
"On" rather than "ALT" should give Mode A.

I just put a 327 in my aircraft - thanks for posting this 'cause it gave
me
an excuse to re-read the manual to verify that "On" is Mode A. I'll check
it tomorrow for some visual feedback that Mode A is active vice Mode C.

This is correct. "On" mode kills ModeC, but allows ModeA. It's the same on
most transponders, even those with analog readouts.

Blind encoders are just that.. Blind, they do not care what the current
proper "altimeter setting" is.

ATC decoders know the altimeter settings for a given area and automatically
apply the correction before displaying.
I've watched entire digital radar displays report everyone 300ft off
instantaneously as the altimeter setting table was loaded into the system, a
momentary blink when there was no corrections, and then the updates as the
new setting corrections were applied to the ModeC data received.

ATC will issue the altimeter setting to the pilot in the event the
"displayed" altitude does not agree with the pilot reported altitude just in
case the pilot has miss set or not set the altimeter for the correct
pressure. In such cases normally about a 200-300ft difference, the pilot
dials in the correct pressure and then either reports a new altitude that
may agree with the reported altitude, or descents/climbs to the reported
altitude and the ModeC now agrees.

It appears that the Garmin 3xx series transponder may have an error in it's
sensor, a leak in the static line to the sensor or something creating a
vacuum near the sensor as it was reading about 700-800ft to high.

You state that the altimeter agreed with the ASOS setting on the ground. At
ground level and not moving (ground speed = zero) does the reported FL
altitude display agree? If they agree, then I would suspect that the static
line might be off the back of the encoder transponder and that in-flight the
encoder is sensing cabin pressure and not outside static pressure. In flight
in C-172s, the inside cabin is slightly lower pressure than outside due to
vacuum effects of a leaky fuselage.

I'm somewhat surprised, if the pilot is part owner and flies this aircraft
regularly, she does not know the operation of her transponder. She can
select STBY, ALT and put in the code, but she does not understand it's
operation.
A nice thing about those transponders.. the VFR button will automatically
load 1200.

BT


"Viperdoc" wrote in message
...
I have flown with a couple of Garmin 327's and now have two 330's. The
pressure altitude readout on the transponder comes (as I recall) from the
blind encoder. It is obviously not connected to the altimeter setting.

So, the encoder could be culprit for the mis reported altitude. I suppose
there could be a difference in altitudes of 700 feet if the day was very
non-standard (such as very cold, high pressure, etc).