Thanks guys, thats question 1 dealt with.
Perhaps a little more explanation on the second one.
1. On later generation EFIS aircraft, the TCAS and RA displays are fully integrated into PFD, ND, or MFDs. [On such aircraft you'd have to lose multiple efis screens to lose all options for a traffic display, by which time your MEL wouldn't allow dispatch anyway]
2. On early efis / non efis aircraft, a typical TCAS display implementation is a seperate TCAS VSI which replaces a conventional VSI, providing the VSI function, with RA's shown as coloured arcs. The centre of the instrument is used to provide a traffic display. [On such an aircraft to loose your traffic display you'd have to have both TCAS VSIs inop, at which point you'd have no VSI so you'd be MEL no go anyway]
3. But there is sometimes a halfway house between these installations, where the PFD/EADI is capable of displaying an RA in some manner (pitch or integrates VSI bands),
yet the ND/EHSI is not capable of showing the traffic display. On such aircraft a seperate display is used, for the Traffic, and it doesn't do anything else. Often its the same physical item as the TCAS VSI but without the air data connections and presumably some pin or config bit set to stop it showing the VSI scale. With this arrangement, the loss of the traffic display doesn't compromise anything else on the aircraft.
I used to fly an aircraft equipped as per (3). I have a recollection (but I'm not sure because its a while back) that the MEL allowed dispatch with
both traffic displays u/s.
The rationale persumably being that the TCAS was still functional, it could generate an RA, and via the PFD you could still fly it accurately. Which of course very neatly illustrates the relative importance of the RA versus the Traffic blips.
So I'm seeking input from anyone else that flies something with a TCAS installation like (3) to see what their MEL permits.
Thanks.
And Humbug, as its nearly that day.
pb