Using the transponder

[CJM]

Is it nessessary to keep the transponder on standby until right before takeoff or does atc have the technology to filter out the a/c on the ground now?

another similiar question- Ive seen lots of guys turn the transponder to standby rather than just turning it off right after landing. Is that easier on the transponder equiptment?

Thanks,

C

[moocow]

Ok no expert here but I doubt they have the ability to tell the difference between transponder on the ground and transponder in the air. The transponder basically broadcast the aircraft location and that may clutter their radar screen if you have it on while on the ground. As for the second question, better to leave it for an AME to answer that.

[200hr Wonder]

Turn your transponder off, it just A. clutters up screens and B. makes people with TCAS scared when they see dots on short final. In fact at busy airports you miss getting the transponder off and ATC will ask you to turn it off.

As for going to Standby, I think that it has more to do with older ones that took some time to warm up before use. So leave them in standby so that they are ready for the next guy. I would suspect that the newer ones don't have the warm up thing going on.

[avyonx]

If it is a busy airport and everyone had there's ON then it would clutter and ATC does not have a filter. There is no rule saying you can't have it on, on the ground. ATC may say turn it off though. So it is best just to turn it on during the T/O roll. Plus what would the TILT check be without the last T........I guess just TIL.

KT76A's and older Narco's should be left in standby because of the older technology. Newer Transponders like 327's and 330's are solid state so it doesn't matter what position you leave them in. Plus you can take advantage of the Auto ON/OFF feature on those. That goes back to the TIL check though

[iflyforpie]

Pretty much very transponder that is installed in your aircraft as of 2010 is solid state. This includes the KT-76, AT-50A, RT-359A, and other ancient transponders that have made it this far.

Ever see a functioning KX-160 Nav/Com these days? Probably not, because those tubes are fragile, inefficient, and hard to replace. But you don't have to go far to find a still functioning (often quite nicely) solid state KX-170 or 175.

I think they put the standby in there for the old guard who wouldn't be comfortable without warming up their radios. But make sure it is off before you start, because high current (an unlikely occurrence, but still possible) will kill any solid state device.

As for ground clutter, I did remember hearing from an ATC person that there is a surface declutter feature on the radar , but there is still TCAS, so make sure you keep it off unless you are on the runway...

[CanAmdelta1]

cjm,

Check the documentation for that aerodrome. At KBOS Boston Logan Intl " Pilots should operate with Mode C Xpdr "on" while on all taxiways and runways.

It really depends on the requirements of each facility. Usually the Airport Diag or the following will give you a good idea: ATIS, Clearance Del, Ground, Tower.

I agree, in the local area, I don't activate xpdr until just before calling tower for takeoff clearance.

[HeadingAltitudeSpeed]

Unless directed to by ATC transponders should be OFF unless the wings are generating lift.

Everything said above is true. We do have filters available for different purposes but will not filter aircraft at airport elevation for safety reasons.

[SuperchargedRS]

Turn it on when you want to be seen by others. View it like your strobes, turn them on when you cross the holdshort line for your TO roll.

The only time I leave my xponder on is if I am at a airport with ground survalence (ASDE-X) where they expect you to do so.

[SAR_YQQ]

I shutdown with the transponder in stby. The master avionics switch takes care of turning it off.

[whistlerboy02]

Leave it on at large US airports like Washington Dulles (KIAD). I got heck for turning my transponder to standby. The Airport Surface Detection ASDE-X needs it.
Here's the other airports and an explanation
http://en.wikipedia.org/wiki/ASDE-X

[CJM]

Thanks for the replys!

I never thought of TCAS (probably cause i have only read about it)

[complexintentions]

The transponder operations will depend on the equipment installed, your company SOP's, and ATC requirements and capabilities. Some of these blanket statements are not correct. With newer equipment some older techniques no longer apply.

For example on our a/c there IS no "Off" setting, only standby. And it's put into TA/RA directly after engine start, before taxi. Every time. Every airport. It goes back into standby as part of the engine shutdown checks, on the stand. The only time it ever goes into "TA-only" is during an engine-out, or in an environment where it highly likely to receive a nuisance warning (ie close parallel visual approaches into SFO). Otherwise it's in TA/RA from engine start to shutdown.

There are inhibits built into the system while on the ground and while on approach below 400' AGL. We will not receive an RA on approach because a/c on the airport are operating their transponders!

But different models and a/c types obviously will have different requirements. Best to adhere to the company SOP's and in the absence of those, the manufacturers recommendations.

[SAR_YQQ]

You're talking about your TCAS not your transponder - two very separate systems.

[wallypilot]

Turn it on when you want to be seen by others. View it like your strobes, turn them on when you cross the holdshort line for your TO roll.

The only time I leave my xponder on is if I am at a airport with ground survalence (ASDE-X) where they expect you to do so.

Exactly. That covers pretty much every possible situation.

And airports with ASDE-X will usually brodacast on the ATIS or have a note on the airport diagram to "taxi with transponder on".

[FlaplessDork]

Don't turn in on unless you are on the runway. I remember reading a case where an airline had a TCAS RA and went around because some guy had his transponder on holding short.

[PanEuropean]

I posted a reply to an almost identical question that appeared on the Pprune forum a few days ago - rather than repeating it here, I'll just provide the link: Using the transponder.

The short answer to the question is that the correct procedure to use is dependent on the level of integration of the avionics system in the aircraft (in other words, whether or not the aircraft air-ground monitor provides the transponder with the aircraft's air-ground status), and whether or not the transponder is capable of operating in a 'ground' mode, when it will only reply to interrogations that are specifically addressed to the aircraft by name (name being either the aircraft registration, or the flight number).

Generally speaking, if the transponder supports ADS-B OUT (either by way of the 1090 mHz extended squitter, or by way of a UAT), it will probably support ground mode operations, but the only way to know for sure is to consult the AFM or the FCOM.

Most transponders that support ground mode operation will provide annunciation when they are in ground mode - see the illustration below for an example. Ground mode is not the same as Standby.

Michael

Transponder operating in Ground Mode

[PanEuropean]

...makes people with TCAS scared when they see dots on short final...

I don't think that would be a concern. The TSO specification for TCAS I and TCAS II calls for suppression of traffic advisories and resolution advisories when the TCAS equipped aircraft is less than 400 feet above ground. Plus, if you are at 500 AGL on final, and you see a target directly ahead of you, at the same distance as the airport itself, that appears with a '500 feet below' indication beside it, it's pretty easy to figure out that the target is an aircraft sitting on the ground at the airport.

The TCAS processor in the receiving aircraft considers the speed at which a proximate aircraft is moving, for this reason, transponder-equipped aircraft that are on the ground will normally not be displayed unless they are moving very quickly (e.g. on the take-off roll). Occasionally a large aircraft that is taxiing quite quickly directly toward a TCAS equipped aircraft (e.g. TCAS equipped aircraft is landing on runway 18, fast-moving taxiing aircraft is travelling north towards the holding bay of runway 18) will appear as a target, but in those cases, the first paragraph still applies.

Michael

[200hr Wonder]

I dunno from my prospective if I am flying an instrument approach to minimums and suddenly quite close to breaking out a filled in dot appears on my VSI where my TCAS is displayed I find it quite distracting at a very critical time of flight. Certainly I know what is happening and can process it out, however at the end of the day I don't think it is necessary.

[complexintentions]

You're talking about your TCAS not your transponder - two very separate systems.

Well, actually I was talking about it as two interdependent systems, seeing as TCAS II rev.7 RA capability isn't possible without both conflict aircraft having mode S transponders. Here's the B777 transponder/TCAS panel:

Don't turn in on unless you are on the runway.

As you can see, there is no facility to switch the transponder off or to standby. And the TCAS has no "Off", only standby.

PanEuropean gives the best explanation as to why there are transponder types that are perfectly acceptable to operate fulltime and in fact, have no way of switching the transponder off. The air-ground logic prevents false alarms. 200HR Wonder, I don't know the vintage of TCAS you are flying but I'm surprised that you're getting advisories on approach, if I understand that correctly. As far as targets showing on the runway I'm landing on, I'd way rather have them than not, thanks!

It comes down to what the capabilities of the gear have, but these statements about operating it like a strobe or whatever for all types just isn't correct.

[c170b53]

For the little guys; I don't think its an issue for ATC as their radar won't pick you up until your airborne.