767-300 & Ivsi Tcas

[Mark McG]

What AC Bus powers the IVSI TCAS display on the 767-300?
Does it run off Left,Right or both?
Does the VSI part run off a seperate Bus from the TCAS display, or do they both run off the one?

Thanks

[QAVION]

Hi, Mark.
On our 767's, I believe the power for the indicators comes off the respective Captain's / F/O's Flight Instrument XFR Busses (individual CB's on overhead panel: Pull these CB's and the indicators blank completely.... no TCAS, no IVSI).

The TCAS computer, on the other hand, only provides data (on databusses) to the indicators (i.e. no indicator LCD display power). If power is removed from the TCAS computer (or the computer fails), no TCAS data would reach the indicators, but they would still function as IVSI's. I believe power for the TCAS computer comes from the Left Main Bus.

If power is completely lost from, say, the Left Main Bus,...i.e. the Bus Ties refuse to allow power from the Right Bus to the Left Bus after a Left Engine Gen failure (and no APU/Ground power available), both IVSI's will still get power from the Right Main Bus via the transfer relays, but the TCAS wouldn't work.

There is only a single TCAS computer, so no redundancy, I'm afraid. Lose power to this and both pilots lose TCAS info.

Hope this helps.
Cheers.
Q. ("767 PIC" fan ;-))

[Mark McG]

QAVION,

thanks for your answer.
In reply to your Q. Yes I am.


Mark