Explain my transponder?

[ARFlyer]

I've got six years and nearly 1000 hours on my GTX330, so YMMV.

10 of our aircraft use the GTX330 box. We have never had any problems. The ones we have problems with are the old Kings and Narcos.

 

[Capt. Geoffrey Thorpe]

When the Encoder is working properly, does that mean the whole system is?

How do we know the transponder is responding to interrogation?

The encoder could be miswired. Or a wire could be broken. Or the transponder could just plain not be working.

But, since ATC is complaining about a discrepancy, chances are the transponder is responding. Otherwise, they would be complaining about something else.

And, to pass the IFR check, the transponder would have to be transmitting the correct numbers back to the IFR check radar / vacuum pump / readout thing.

 

[poadeleted20]

The encoder could be miswired. Or a wire could be broken. Or the transponder could just plain not be working.

But, since ATC is complaining about a discrepancy, chances are the transponder is responding.

Could be? Chances are? How in the world could the controller be seeing a code and altitude (right or wrong) if the transponder were not responding or "just plain not working"?

And, to pass the IFR check, the transponder would have to be transmitting the correct numbers back to the IFR check radar / vacuum pump / readout thing.

What does the vacuum pump have to do with this?

 

[Capt. Geoffrey Thorpe]

Could be? Chances are? How in the world could the controller be seeing a code and altitude (right or wrong) if the transponder were not responding or "just plain not working"?

Just answering the question asked.

What does the vacuum pump have to do with this?

Because that is how the "altitude" is generated for IFR (or VFR) certification. Ever watched one? They have a big box. The box has a hose coming out of it and indicators on top. It also has a wire that goes to the antenna that triggers the transponder. Inside the box is the transmitter/ reciever that interrogates the transponder. Also inside the box is a vauum pump that connects to the hose that comes out of the box that connects to the static system. The displays on top are connected to the vacuum to display the "altitude" and to the reciever which display the code and altutide returned by the transponder. Plus (IIRC) there is a display of the actual transponder frequency. Perhaps a display of the power as well - but it's been a while since I looked at one closely.

 

[flyingron]

I've watched it. There are more than one test done. The altimeter is checked against a known reference number of altitudes going up in altitude and then coming back down. There are also hysteresis tests at a number of altitudes as well as an overall static leakage. In addition the transponder reported encoder output is checked against the reference at a number of altitudes. I prefer the holistic approach of leaving everything in the plane and testing it by sucking on the external static port, however it is acceptable, to do some of the testing on the bench.

 

[poadeleted20]

Just answering the question asked.

Well, the "chance" in the question as asked is 100%.

Because that is how the "altitude" is generated for IFR (or VFR) certification. Ever watched one? They have a big box. The box has a hose coming out of it and indicators on top. It also has a wire that goes to the antenna that triggers the transponder. Inside the box is the transmitter/ reciever that interrogates the transponder. Also inside the box is a vauum pump that connects to the hose that comes out of the box that connects to the static system. The displays on top are connected to the vacuum to display the "altitude" and to the reciever which display the code and altutide returned by the transponder. Plus (IIRC) there is a display of the actual transponder frequency. Perhaps a display of the power as well - but it's been a while since I looked at one closely.

Now you're talking about the test equipment, not the aircraft?

 

[John Collins]

Having operated an avionics shop for six years, I would recommend you replace the encoder. If you spent more than one visit to the avionics shop and didn't replace the encoder, you have probably wasted your money. The ACK-350 sells for under $200 or about two hours labor at a typical avionics shop.

 

[Capt. Geoffrey Thorpe]

Well, the "chance" in the question as asked is 100%.

purd near

Now you're talking about the test equipment, not the aircraft?

Which is what I was talking about in the first place:

"And, to pass the IFR check, the transponder would have to be transmitting the correct numbers back to the IFR check radar / vacuum pump / readout thing. "
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The IFR check is done with test equipment attached to the aircraft.