Does the TCAS control swtich on the 744 also work the transponder? so if i set it to TA/RA will the transponder turn on? because a few days ago when i got into the cockpit of a plane on the ground the mx guys turned the swtich to TA/RA to show us the traffic around the airport. and i was curious because in the PMDG 744 i assumed that switch also turns the transponder on, and thus thought that it might clutter the display for ATC.adam

Adam-Most modern airplanes have an air/ground mode sensor that inhibits transponder reply signals that would clutter ATC's view of the world.The transponder will still give you TA feedback on the display however- as it is important situational awareness during the pre-takeoff phase- especially if ATC puts you in position and doesn't issue your clearance right away....

ok, thanks alot for the quick respone and clearing that up for me.adam

Its also becoming common practise at many Airports now to have the transponder on while on the ground, at KMCO and EGLL its a requirment for example.The Mode S transponder "squit" can be used for ground movement monitoring by atc.Our SOP is now to turn the transponder on just prior to brake release on push back,and not to turn it off until brakes on arriving on stand.regardsJon

If you get a code change do you normally switch to standby first before altering the code ?David Miles

Most modern systems do this automatically when a new code is entered so there's no requirement to do so.EHAM also requires you to switch on the transponder on the ground.Have fun and a happy new year to all!