A few TCAS odds and ends

[Capt Pit Bull]

Well, I've answered dozens of TCAS related questions over the years.... now its my turn to ask some please!

1. I seem to recall that there were some TCAS installations that had the ability to show traffic absolute pressure altitude as well as relative. e.g. you are at FL240, other aircraft is at FL230, you could flick a switch to swap the data tag from -10 (relative) to 230 (absolute).

Is anyone still using something like that, or is it strictly v6.04 (or even earlier) vintage?

2. Is anyone is operating a type with a seperate traffic display (i.e. Traffic not integrated with EFIS Nav Display, but with the RA shown on the EFIS PFD rather than a TCAS VSI). I dont have ready access to a wide range of MELs these days and I was hoping you might take a glance at your MEL and see what the deal is if your traffic display is u/s.

Regards all,

pb

[herbert23]

My former company operated some 737 300 where you had the possibility to switch between the normal indication and the indication of the actual FL of the other traffic. That means if we were at FL 300 and the other traffic was at 310 we could switch the indication from +10 to FL310.
Some of the 737s also had the traffic display integrated into the vertical speed indicator.
That was about two years ago in central europe

[roljoe]

Hi,

1) on the Learjet45, we have the possibility to select the absolute mode for surrounding traffics, but the default mode is "relative"...It means that the system returns automatically to "rel..alt values" after 20" when abslo.. has been selected..

2) Usually the tcas display is allocated to the efis n°3 (= mfd /copilot) but can be transfered to the n°2 (mfd/captain)..

No way to invite the picture on a PFD...

Should a RA wakes up the crew..:E a red and green arc will be displayed on both pfd

hopes this enrich your request a little bit.

merry Xmas..

[galaxy flyer]

Capt PB

You've answered my questions on TCAS, so here are some answers for you.

On the Honeywell Global Express V7.0 installation:

We can display ABS or REL altitudes, though I've not run into anyone who does. Next I'm out in the plane, I'll try it and get back.

The neater part is that the RA is displayed on the PFD as "green" and "red" boxes, showing both pilots exactly where to put the pitch for the correct RA action. Very intuitive and simple; also reduces overshoots or too rapid reactions, just raise or lower the pitch to put in the box and "Bob's your uncle".

GF

[Capt Pit Bull]

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

[Graybeard]

One option on the first TCAS installations used a pair of RA-TA-VSI which display both traffic and RA red-green arcs on a CRT or LCD VSI.

Another option was a pair of RA-VSI which were just electro-mechanical VSI with a ring of red/green LED added to the perimeter. The traffic display was usually the WX radar indicator.

When Boeing upgraded the EFIS symbol generators on the 75/76/73, they provided both RA advisory on the EADI and traffic display on the EHSI. I haven't heard of a plane with RA advisories on the ADI, and traffic on the VSI.

Back then, TCAS was on a 10 day MEL.

GB

[Denti]

Same as herbert we had some older vintage 733 with VSI integrated TCAS display which showed in the event of an RA a red and green band. I seem to recall that at least one of them showed the usual cues on the PFD as well, no display on the ND there.

However TCAS was on a 10 day MEL back then which has been reduced to 3 days since.

[Graybeard]

The original 733 had ElectroMechanical instruments for ADI and HSI, no EFIS. Southwest continued buying that configuration forever, I believe, although the 757/767 EFIS became available in the 73 about 1984. The E/M ADI had no way to display RA, as it didn't even have a vs display. Now it's possible somebody retrofitted an EADI in an E/M 733, without a companion EHSI, but I can't imagine why. The most bang for the buck is in the EHSI.

I'm curious as to the operator of such a configuration, and year it might have been.

GB