400Rulz

After some time looking through the manuals, I have been unable to find which altimeter the transponder on the 744 takes its information from. On the 767, it was the Captains altimeter, regardless of which transponder was selected (L or R). Can anyone enlighten me, and provide a reference?
Thanks in advance.
-400R

tie domi

transponer left onn left, cm1 .eg if left or centre a/p use left transponder to report

Milt

Another Transponder Question

A transponder obviously cannot respond on the same frequency as that of the interrogating signal. Is there a fixed frequency offset to the ground signal for aircraft transponders?

For space vehicles there is evidently a 240/221 relationship to the relative frequencies to somehow enhance accurate ranging by detectable doppler shift.

400Rulz

Thanks Tie, got that, and when right a/p engaged, use right transponder. But that doesn't tell me which ADC is being used for transponder information. I know that the R autopilot uses the R ADC and similarly the L a/p uses the L ADC, but does the R transponder use the L or the R ADC?

mnttech

60 MHz, the ground TX's on 1030 MHz, the airborne on 1090

Rainboe

The transponder should use altitude indications from the associated ADC controlling each side's altimeter. The reason is that altimeters can vary between each other by 100' or more, and the transponder, if it's not using that side's altimeter, will always be indicating on radar a slightly incorrect altitude.

tie domi

right transponder right adc,all trough transfer busses see capt,s transfer bus for clarification

CJ Driver

One of the commonly overlooked procedures associated with RVSM operations is that your active transponder must get the altitude data from the same place as the autopilot altitude hold. If you have an autopilot that follows the altimetry system of whichever side is the PF, as some do, then you should make sure that you flip the transponder (or transponder source) accordingly.

Conversely, if your transponder can only receive data from the LH air data computer, then you must only couple the autopilot to the LH ADC when in RVSM airspace.

NSEU

The ATC uses the Captain's selected ADC if the ATC is in "L" and the F/O's selected ADC if in "R". Look at the instrument source select switches outboard of the CRT's(or LCD's as applicable).

Our 767's can't be the same as your 767's. We use both Left and Right ADC's (with inputs from the instrument source switches as per the 744)