Transponder

[B737]

Dear all!

I need a bit help in relation of transponder usage.

Taxi, line up and tcas settings.

Thank you.

[Litjan]

When you are about to push back or start taxiing you should select the Transponder switch to AUTO. This will make the transponder ON THE GROUND send a coded reply when interrogated (so that ATC can see where you taxi on the airport) but will not send other information, so aircraft flying overhead will not "see" you on their traffic display. Once the plane lifts off, it will also reply with altitude (so TCAS on other aircraft can work).

When you enter the runway you should set the TCAS mode selector to TA/RA (so that your aircraft can react to other aircraft´s tranponder signals).

When you leave the runway after landing set the TCAS mode selector to OFF again.

After parking the aircraft, set the Transponder switch to STBY again.

Cheers, Jan

[B737]

Thank you Jan !

Just 2 more in this topics.

On newer atc mode panel we have alt select to off. What is the reason?

 

2. Tcas panel has above and below.

When and why do we have to use?

 

[Litjan]

Older TCAS systems can select IF they want to transmit Altitude information or just the transponder code. I think newer systems will always display altitude information, there really is no reason to NOT transmit it (unless you want to bust an airspace and not get caught!)

The ABV and BLW governs the DISPLAY of traffic on your EHSI, it does not change how TCAS reacts to other traffic. If you select BLW you can see traffic far below you (range +2700/ -8000 feet, iirc) - if the switch is in the normal position the altitude range is +/- 2700 feet iirc. only.

[B737]

Thank you, very very good explanation. Promising the last of the year. !

I have attached one old fashion panel.

on this where would you set the xponder for taxi? Am I right, that in this case the alt should be off ( as in the picture, center )