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Transponder / ADSB question

RFazio

Well Known Member
I've been flying my friends RV-8. He's got a becker transponder in it with mode S and ADSB out. The tower told us he did not see the transponder. Then we go and look on Flight Aware and there it is. Showing the entire flight. How can the tower not see our transponder, yet we show up on flight aware? What's going on? He thinks it's mode S working, but the mode A & C are not. our tower only looks for mode A? I'm skeptical. Any ideas?
 
I've been flying my friends RV-8. He's got a becker transponder in it with mode S and ADSB out. The tower told us he did not see the transponder. Then we go and look on Flight Aware and there it is. Showing the entire flight. How can the tower not see our transponder, yet we show up on flight aware? What's going on? He thinks it's mode S working, but the mode A & C are not. our tower only looks for mode A? I'm skeptical. Any ideas?

Request an ADSB performance report from the FAA. That will give you some metrics about your transponder and ADSB transmissions.

I don’t have the url handy, but I’m sure it should be easy to find.
 
There are a few things to unpack here...
1) ADS-B and transponder are two separate systems, even with a box that does both.
2) Some ATCTs (control towers) have RADAR displays, and most of those DON't see ADS-B targets. (The numbers with ADS-B change as new tech rolls out)
3) A transponder does mode S or mode A, but not both - and both do mode C
And,
The ADS-B Performance Report is ONLY looking at ADS-B transmissions.

Step one is to be sure the transponder is in the ALT mode.
 
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mode A: squawk code only
mode C: squawk code plus altitude
mode S: same as mode C but ATC can control it a bit (e.g., tell it not to reply)
mode S-ES (some companies just still use "S" and you have to read the fine print): mode S plus "extended squitter", which is extra data bits with the ADSB-out information.

So your friend needs to identify what specific Becker transponder he has. I'm guessing he has a mode C transponder, and a separate UAT device sending out ADSB info on 978 MHz. These work independently, and could easily explain the "no transponder" from the tower, but "ADSB working on flight aware". If he has a mode S-ES it would be a strange failure, but perhaps his altitude encoder or control head has somehow failed in a strange way. But first verify what type of Becker (model number) he actually has.
 
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