Transponder Fault

[Witmo]

Yesterday, although I had dialed in the discrete 4 digit code ATC had assigned me, Approach said they were still seeing 1200 as my transponder readout. I redialed all four digits and cycled the transponder to off and back to ALT with ATC saying they were still seeing 1200. They confirmed my position relative to the VOR. My transponder is an ARC RT359A and it was just certed less than 10 flight hours ago. Could this be a fault on their end? I was fairly low (1000 AGL) and about 12 miles from the radar.

Tim

 

[gismo]

Yesterday, although I had dialed in the discrete 4 digit code ATC had assigned me, Approach said they were still seeing 1200 as my transponder readout. I redialed all four digits and cycled the transponder to off and back to ALT with ATC saying they were still seeing 1200. They confirmed my position relative to the VOR. My transponder is an ARC RT359A and it was just certed less than 10 flight hours ago. Could this be a fault on their end? I was fairly low (1000 AGL) and about 12 miles from the radar.

Tim

With mechanical switches for the code, the only way you transponder could sqawk 1200 with another code dialed in would be with the knobs turned on the switch shafts.

 

[SkykingC310]

I too have had xponder troubles. It's a mystery to me. I often rented planes from the flight school I attended to make trips to see my family. I'd usually take whatever I could get, you know, whatever the flight schedule would allow to be away for two or three days. But my first choice would be the 1998 172R. This was the newest bird in the fleet and the most comfortable for my family. But more than once, I've had xponder problems with it. Often, ATC would receive the primary return, but not the secondary. Which I think means, they see me, but can't determine my altitude, right? And when I'd get back after a trip, I'd always write it up as a sqwak. But, sure enough, the next time I'm flying, I get the same reaction from ATC. I have to pretend like it's the first time, every time, ya know? "Oh, ah, I'll have the guys check it out when I get back, thanks." It's annoying that they can't fix the dang thing. Well, I haven't flown that plane in a while, I don't even live there anymore, but I still think about it and wonder why it never worked right for me. And yes, I had it set to ALT.

 

[Skip Miller]

Often, ATC would receive the primary return, but not the secondary. Which I think means, they see me, but can't determine my altitude, right?

Not quite.

The primary return means that the radar receiver is picking up the reflected energy from its radar transmitter. So yes, they can see you but the range might be limited. It is like flying with the transponder OFF.

The secondary return comes from the transponder. When it detects the radar pulse from the transmitter, it responds with a pulse that looks like an echo but with much higher power. This secondary return also lets the radar see you and because the pulse is stronger, it can see you from a greater distance. However, there is still no altitude information. It is like flying with the transponder ON (but not ALT).

The altitude information comes from the transponder operating in Mode C. Mode C encodes your altitude and returns the information with the secondary response. For mode C to be working the transponder has to be set to ALT.

-Skip

 

[Witmo]

I flew again today and asked Approach to check on my transponder return. They gave me a squawk and told me to ident. This time they said everything looked good. I guess I'll keep my eyes open for a good deal on a solid state transponder but for the immediate future it looks like this one might last a little longer.

 

[Stache]

If your keep squawking the wrong number ATC will notify the local FSDO and they will send you a letter saying to have your transponder checked, repaired, or replaced.

Stache

 

[Dean]

Sometimes I wonder if it is our equipment that cause problems or ATC's. I fly VFR from UUV - ADH several times a year. When I depart UUV I call up Kansas City Center for flight following. The last trip I made had some interesting traffic with center and approach. KCC had followed me to Springfield and the handed me off to them. Springfield approach said they did not have me on radar and to recycle my transponder. After several resets they started picking me up. Springfield then handed me to Razorback and then I was handed off to Menphis. Menphis ask me if I was going direct to ADH and I answerd "affirmative". He then told me to turn 15 deg left to get on course. Well being the new pilot, I fly with two GPS's, one dash mounted moving map and one handheld. Both showed me on course and I was right on with my chart. After thinking about it a minute I politely replied, "Menphis center, I have 2 gps's on board and they show me on course. The controller in a pi$$ed off voice replied, then stay on YOUR course and contact Ft-Worth center on 133.4. Well to end this story I made my trip just fine and Ft.Worth never said anything about being off course. I was at the edge of Menphis' radar, so I wonder if that was the problem?

 

[wsuffa]

The controller in a pi$$ed off voice replied, then stay on YOUR course and contact Ft-Worth center on 133.4. Well to end this story I made my trip just fine and Ft.Worth never said anything about being off course. I was at the edge of Menphis' radar, so I wonder if that was the problem?

My bet is that you were going to cross the boundary and then back. Memphis wanted you slightly off course to track you and keep you in radar contact.

You ever read Don Brown's columns on AvWeb? This is one of his peeves with GPS direct.

 

[Merf]

During hurricane Rita, I evacuated recently purchased N9566H to Abilene, Texas from 45R for 3 days. On approach to Abilene I was informed they were not getting my transponder (Garmin, less than 1 year old). It was a weekend, and I needed to get back -- the guys at Abilene said say come in and work on it (I had to go back into a military controlled TFR and sure wanted the transponder). $450 later I returned with my special clearance back into 45R. Guess what. Military controllers couldn't see me! Well, it didn't much matter, as they had other problems to contend with and I flew on into my little airport without incident (I checked in with them and that's basically all they wanted).

One week later was going to take some electricians up for a ride (we had Entergy folks camped out at the airport). On preflight, I got to looking at the antennas -- I noticed a little (and I mean little) grease/scum on the leading edge of the transponder attenae. Wiped it off. Hadn't had a problem since.

Live and learn.


Merf

 

[JHW]

if you start go get slight off codes on that RT359A, you can take the face plate off and very carefully clean the little foil discs with a pencil eraser. Sometimes works, sometimes causes more damage but you were on your way to the shop anyway. This is for the type of problem where they give you 4510 and then say they are seeing you squawking 4610, no idea how it could stay at 1200.