Use of transponder on the ground

[Zoyberg]

It does not give this as a requirement in our SOPs.

It does mention in many aerodrome booklets that transponder use is required during taxy.

There are many large airfields I visit in Europe and the Middle East and Asia where I am told by the trainers it is required (even though this is not mentioned in the booklets or the Jeps area supplement).

Anyone know where this is written please?

[Sniff]

Don't know where its written, but its down to the new generation of surface movement radars (radar in this context is probably the wrong word!) which rely on transponder returns to generate the ground movement picture. Hence no transponder - No display of traffic to the controller.

[FLX/MCT]

Can the use of Transponder on the ground be the cause of a TCAS TA/RA or is there a special "ground mode"?

regards
luke

[plugster]

In FRA it is done by software and they had a long way to go before this feature was implemented. So before the software was able to link the callsign to the blip it was just a blip without any further information.

[Spitoon]

It's mode S that most of the modern systems use. Although operating procedures are slowly harmonising in some regions, they could hardly be considered to be standardised. Afraid the best place to look is going to be the relevant AIP pages.

[Check Airman]

Can the use of Transponder on the ground be the cause of a TCAS TA/RA or is there a special "ground mode"?

Private pilot speaking...I understand that most modern systems automatically switch to TA ONLY below 1000ft RA to inhibit nuisance warnings. I'm guessing that the system logic would look at the altitude and speed of the target to determine if it's on the ground, but that's pure speculation.

[tuskegee airman]

Spot on Check Airman.

FLX/MCT- while taxying you can turn the TCAS off while leaving your transponder operating if required by local procedures.

Speaking only for Airbus their FCOM 1.34.80 states in part that "... if windshear, stall or GPWS are triggered or aircraft below 500ft agl all TCAS aural messages are suppressed." (minor alt differences depending on whether climbing or descending).

Drivers of other types can speak to their specific aircraft.

[ahramin]

TCAS/ACAS have no logic for determining if an aircraft is stationary or on the ground.

Warnings are suppressed as already pointed out.

[Admiral346]

Suppressing the TCAS RA is of course dependent on your Radio Altimeter, how else would it be done on any type?

Nic

[SlowAndSilly]

I have started to always put the transponder to XPDR when the push/taxi starts because I don't bother remembering the airports where this is a requirement or not.

If the airport isn't equipped with this new transponder surface monitor system (A-SMGCS?) I have been told that "my" squawk won't bother anyone.

And the data sent out are not capable of trigging TCAS equipment (XPDR-mode)

[WindSwept]

Just a little insight from Air Taffic here.

If you are operating on an airfield that employs ground movement radar. Transponder use can be required, in which case the radar picks you up and identifies you on the blip on the airfield layout they have. Used at places where low vis often occurs, or large airfields to prevent collision and to increase efficency.

In terms of airfields not employing surface movement radar, the radar room doesn't get interference from your transponder being active whilst on the ground, as SSR radar supresses transponder codes on the ground, or airfields would just be a haze of transponder codes.

[bookworm]

Can the use of Transponder on the ground be the cause of a TCAS TA/RA or is there a special "ground mode"?

A Mode S transponder includes an on-the-ground status flag in its reply. Thus if you have Mode S, you can simply leave it on.

A Mode A/C only transponder has no such output, so it should be switched on only for departure and off again after landing.

[Miles Magister]

Guidance can be found here http://www.eurocontrol.int/msa/gallery/content/public/documents/ACAS_Bulletin_9_Jul-07_update_Nov07.pdf in the Eurocontrol Bulletin 9.

Other bulletins can be found here EUROCONTROL - ACAS II Bulletins and Safety Messages (http://www.eurocontrol.int/msa/public/standard_page/ACAS_Bulletins_Safety_Messages.html)

All well worth reading.

MM

[lalbak]

Flying out of Amsterdam I know its mentioned somewhere in the Jepp plates in the airport briefing and ATC well call you on it if you do not have your transponder on XPDR mode as soon as you start taxiing.

[747dieseldude]

I have come across airports that tell you to turn it on on the ground, and some airports that specifically tell you to turn it off. Some even state the requirement in the ATIS.
By 'it' i mean the transponder. TCAS should always be off on the ground, so you should use the 'auto' position on your box, or 'xponder'.
I guess the safe way would be to use the transponder on the ground, and let ATC tell you to turn it off if it bothers them.
My airline has put a line in the before start checklist and in the shutdown checklist for remembering to turn it on before push-back and off when at the gate.

[dusk2dawn]

From a number of sources [Eurocontrol ++] we have collected the following:

Advanced Surface Movement Guidance & Control System (A-SMGCS) is in an operational test phase at CDG, VIE and MUC but has also been installed (or are under installation) at a bunch of other european airports like: CGN, LYS, TLS, MAD, Barcelona, Oslo, Stockholm, Prague, FCO, Malpensa, AMS, Riga, LGW, LHR, BRU, FRA, HAM, DUS, Palma De Mallorca, CPH, Zurich, Geneva, Paris Orly.

As I understand it, Eurocontrol likes you to turn it on from the time you request push.

[747dieseldude]

To: All airlines operating into the United Kingdom
Dear Colleagues,
This message is being circulated to highlight an amendment to the UK AIP with regard to the requirement for use of Squawk A2000 on ground with effect from 12 February 2009. In essence the change seeks to harmonise the use of Squawk A2000 on ground as follows:

"Unless otherwise instructed by ATC, Mode S transponder equipped aircraft on the aerodrome surface should select Mode A code 2000 when under tow; or parked and prior to selecting OFF or STDBY."

[Boingboingdriver]

if u have TCAS, just select the mode XNDR or ALTOFF NOT TA/RA.
It is especially important during low vis weather,so controller can track your progress.TARA only when entering runway in use.It is nerve recking to see alt reporting of an aircraft taxiing on // taxiway when you are taking off in low vis conditions.
If it is not written on your Jepps, you dont need to do it unless of course your SOPS require you to.

Captstd:E

[Denti]

Really depends on the kit you have equipped. Ours for example are set in AUTO and do as Mode S Transponders should: set the ground flag when on the ground so you won't get any altitude reports from them.

[Henry VIII]

Miles Magister post #13 (http://www.pprune.org/tech-log/350412-use-transponder-ground.html#post4522643) with it's links explains the scenario as best as possible.
Ciao :ok:

[Graybeard]

This is misleading: "if u have TCAS, just select the mode XNDR or ALTOFF NOT TA/RA.
It is especially important during low vis weather,so controller can track your progress.TARA only when entering runway in use.It is nerve recking to see alt reporting of an aircraft taxiing on // taxiway when you are taking off in low vis conditions."
--------

The transponder is the only device replying to TCAS, or replying to ATC SSR. If the Mode S transponder (required with TCAS) is reporting ON Ground, its replies will be ignored by TCAS interrogators in the area.

If the transponder is reporting altitude within 180 feet of runway elevation, as in a Mode C reply, it will likewise be ignored by TCAS in other aircraft. Do not turn off ALT replies (ALT OFF) on your ATC/TCAS control panel unless ordered by ATC, or your transponder will reply with no altitude, maybe causing false TA alerts to other aircraft. (The false alert part depends on the ON Ground priority in the calculations, which may not be consistent between TCAS and transponder manufacturers.)

TCAS coordination between planes is via the transponders. Your TCAS interrogates the other plane's transponder and acts on those replies. Your TCAS reports to the other aircraft via your own transponder. There is no TCAS to TCAS direct link, as there is no ATC SSR uplink to your plane, save for the reply lamp of the Mode AC world. The TCAS processor is just an airborne ATC Secondary Surveillance Radar.

A good way to operationally test your TCAS on the ground is to block the radio altimeter RF signal so it thinks you are above 2500 feet. Your TCAS then thinks it is at altitude, and will give you TAs and RAs from real traffic in the area. It has no effect on airborne traffic, as your transponder is still reporting ON Ground, and within 180 feet of field elevation.

GB

[Boingboingdriver]

Greybeard,

Please explain what in my previous message was misleading...
I NEVER SUGGESTED TO SWITCH TO ALT OFF IN THE AIR:ugh:,however TARA is deselected during the AFTER LANDING flow.
ARE YOU suggesting to keep the TARA mode until shut down?so we could all see eachother?:hmm:Map is not showing aircrafts with ALTOFF on the GROUND but those with TARA selected.
I wrote seeing an aircraft on your map mode with altitude reporting ZERO on the taxiway parallel to runway interesting to say the least during a low vis take off.
XNDER/ALTOFF is required by many airports before asking for pushback.

Capt STD:E

[ACMS]

I can only speak about Asia.

We NEVER turn off the XPDR or the TCAS in our CX 777's ( unless the NNC requires it to TA only )

-The modes S knows it's on the ground and wont trigger a TA/RA in another nearby A/C.

-now days we can NEVER see other A/C on the ground on our ND, even if they have their XPDR switched on. Since they modified the system I have NEVER seen another A/C TCAS target on the ground. ( We used to get the occasional TA from a parked A/C.)

-However you CAN see the airborne A/C coming and going.

They modified the system logic about 3 years or more ago, or was it when they introduced mode S? Not sure but it works fine. :ok:

[Boingboingdriver]

I have seen on my PFD a yellow tcas symbol showing alt 0 during take off many times(paris and Vienna)...I believe it was due to both of us (me taking off) having TA or TARA mode selected.
I am aware there is no Traffic advisory /or resolution advisory triggered on the ground:cool:
Capt STD:E

[Denti]

On the PFD in a 737?

Besides, it really depends what kind of box you have fitted and what the company advised SOPs for that box are. For ours (yes 737s as well) it is to let the transponder in TA/RA all the time except during degraded performance where we switch to TA. TCAS as such shouldn't have any problem with that as was described above very aptly by Graybeard.

[Graybeard]

"I have seen on my PFD a yellow tcas symbol showing alt 0 during take off many times(paris and Vienna)...I believe it was due to both of us (me taking off) having TA or TARA mode selected."
Capt STDhttp://static.pprune.org/images/smilies/evil.gif

If you have seen that, Capt, your TCAS System has failed. Based on your own radio altimeter, any transponder return reporting altitude within 180' of ground is to be suppressed - not displayed. Now, if you have seen a yellow blip with no altitude tag (not 0), that is quite normal, as without an altitude in the reply, your TCAS cannot determine the other aircraft's altitude, only distance and rate of closure.

That is precisely why you are wrong in turning ALTOFF on the ground. You should never, ever, turn off ALT unless specifically instructed by ATC. There are only two conditions in which ATC will ask that:
1. Your altitude reporting is erroneous and you have no backup.
2. ATC SSR is overloaded. That's unlikely.

Putting your transponder in Standby will of course stop the altitude replies, so the ALT switch position is irrelevant.

When Mode S was in final development in 1987, I argued with the design engineers to remove the ALT switch from the control panels entirely, but they couldn't without an FAA mandated change.
---------

A bit off topic, but relevant:

The FAA stated that for Mode S (and TCAS) retrofits, the altitude source for the transponder be the most accurate in the airplane, i.e. the CADC digital or synchro output (with integrity monitoring), and not the Gilham code that is used by the older ATCRBS transponders. There is no monitoring of Gilham code, so errors in altitude reporting happen.

Sure enough, the KAL 747 fleet was retrofitted with TCAS (and Mode S), but they didn't use the best CADC altitude output. A few years later an error in the Gilham code had one KAL 747 reporting 10,000 when it was actually at 7,000, and it nearly collided with another 747; JAL, I believe.

GB