Use of transponder on ground

[Marcus Haraldsson 1359974]

Hi,

 

I've got a question regarding using theuse of transponder on the ground.

So, I am aware that in real life pilots usually tend to set their transponder to ALT RPTG OFF during taxi/pushback, and when they get onto the runway they set it to TA/RA.

Now, my question is; when I flew to CPH, the ATIS said "squawk Charlie on push" which I [Mod - Happy Thoughts]ume means that you should set your transponder to "on" meaning TA/RA or XPNDR. But if that is the case, why does just CPH (and maybe some other airports) have it differently than other Airports that just require ALT RPTG OFF, since why would they need to have your altitude reporting and not just your squawk? And if I would still set it to ALT RPTG OFF, would ATC ask me to go to squawk mode Charlie since that what it said in the ATIS?

 

Also, I am wondering if you should set you're transponder to TA/RA while corssing a runway, and after you've crossed it, if you should turn it back to ALT RPTG OFF?

 

Thanks in advance!

[Sebastien Bartosz]

Some airports have surface movement radar which requires you to turn on your transponder.

On VATSIM, some airports simulate this and some dont.

[Marcus Haraldsson 1359974]

Ok, thank you for the answer.

 

Now, when crossing a runway in an Airport without a surface movement radar, should you set your transponder to TA/RA while corssing the runway and then turn it back to ALT OFF when you've corssed the runway?

[Thimo Koolen]

It all depends on the airport. Most USA airports require squawk mode C when you want your pushback. Most European airports (especially larger, international airports) have a ground radar which doesn't need mode C before you take off. It all depends on which airport you fly from.

[Simon Kelsey]

The problem is that currently the VATSIM network protocol only supports two transponder modes: altitude reporting (mode A+C) and standby (ie off).

 

This is problematic in situations like those described above where airports with surface movement radar require the transponder to be ON (so that the mode A code can be correlated) but not necessarily sending altitude information, or in mode S. In real life, as you say, one would select mode A only (which may be labelled ALT RPTG OFF), but there is no way to do this with the current network infrastructure. The workaround if the controller needs to see your mode A code for the surface movement radar is to ask you to select mode C, which in most cases is tied to the TA or TA/RA position.

 

However, as mentioned above it varies depending on where you are and some airports will want you to select standby on the ground to reduce clutter. So check the ATIS/local VACC website for the procedures for whereever you are flying to on the day.

 

It would be lovely IMO if the network protocol could be upgraded to support the other modes (and particularly mode S): the controller clients are now capable of it and most aircraft have properly-simulated transponders with all the relevant positions, it is 'just' the network protocols that need developing!

[Marcus Haraldsson 1359974]

Thanks for the response!

 

Now, on some charts it's stated "Select [Mod - Happy Thoughts]igned transponder Mode A and active Mode S, set to AUTO if technically AVBL." and "Select AFCT identification feature if AVBL, before activating transponder"

Does the first statement mean that I should use ALT RPTG OFF during taxi since that is Mode A, and does the second statement mean that when I turn the transponder on, I should press IDENT?

[Simon Kelsey]

Does the first statement mean that I should use ALT RPTG OFF during taxi since that is Mode A

 

Yes -- essentially they want the four-digit mode A code so the radar can tie your blip up to a datatag, but they don't need the altitude reporting info (sometimes also labelled XPDR).

 

does the second statement mean that when I turn the transponder on, I should press IDENT?

 

No. It refers to a Mode S function which isn't functional on VATSIM.

[Marcus Haraldsson 1359974]

Ok thanks,

 

Even though the identification feature does not exist on VATSIM, I'm kinda interested to briefly know what it is, and if it exist on common aircraft such as the 737.

 

Thanks in advance

[Wim Sjoholm 1133704]

Ident makes your radar tag flash on the controllers screen. There's an ident feature on VATSIM as well, not sure if it's a proper mode S implementation tho. You shouldn't press the Ident button on your pilot client unless your controller specifically instruct you to do it

[David Zhong]

"Ident" and "Aircraft Identification" are different things. The latter is a function of Mode S transponders which sends the callsign of the aircraft.

[Simon Kelsey]

Ok thanks,

 

Even though the identification feature does not exist on VATSIM, I'm kinda interested to briefly know what it is, and if it exist on common aircraft such as the 737.

 

Thanks in advance

 

In brief:

 

The basic transponder interrogation modes are:

 

Mode A -- the transponder sends a 4-digit code when interrogated. This 'squawk' code is [Mod - Happy Thoughts]igned by ATC, entered by the pilot and the result is that the ATC computer systems can 'correlate' a Mode A code with a flight plan (the computer knows that code 1234 is [Mod - Happy Thoughts]ociated with flight BAW123). This enables the computer to display more detailed tags on the controller's screen.

 

Mode C -- the transponder sends the aircraft's current pressure altitude when interrogated, so the controller can see this information as well

 

Mode S -- this is a newer standard and enables lots of additional information to be downlinked to the controller -- things like current IAS (previously controllers could only see ground speed calculated by the radar), MCP selections and much more. This information can also be shared between different aircraft for use with TCAS II resolution advisories etc. Unlike the old Mode A+C transponders where the identification of the aircraft on the controller's screen was dependent upon the controller [Mod - Happy Thoughts]igning a 4 digit squawk code to a specific aircraft and the computer systems using that code to tie up the flight plan with the radar return, Mode S transponders have permanent hexadecimal addresses. The crew tell the transponder their ATC callsign for a particular flight (usually through the FMC -- if you've ever wondered what that "Flight Number" field is for, this is it: it's why it's important to enter the exact ATC callsign in there (e.g. BAW12A) rather than the commercial flight number (e.g. BA1212)). This means that the controller can see (amongst other things) a tag with a flight's callsign without having to tie up a flight plan to a 4-digit mode A squawk code -- in effect, the callsign is broadcast directly.

 

Mode S is now a requirement (certainly in European airspace) and so all commercial transport aircraft like the 737 will be equipped with Mode S transponders.

 

However, as I say, we don't have Mode S on VATSIM as yet, just standby and Mode A+C.

 

The "aircraft identification" feature referred to above is basically an instruction to make sure that the Mode S transponder is sending the aircraft's callsign (i.e. make sure it's entered correctly and that the transponder is switched ON in Mode S).

 

"Ident", as mentioned above, is a different feature common to all transponders and provides a way for ATC to confirm that they are definitely looking at the right blip (thinking back to the way in which flight plans are correlated with Mode A codes, it should be obvious that it is possible, either through computer error or input error either on the controller or pilot side, for a plan to be correlated with the wrong aircraft). This is why you should only press the ident button when specifically asked to do so by a controller: just seeing a blip light up doesn't help identify it! However, if you ask a pilot to press the ident button, and their blip lights up as a result, that's an indication that you definitely have the right data.

[Trent Hopkinson]

I usually look out on the ground chart for something like:

 

[Andreas Fuchs]

In the real world we operate our Mode S transonders at all times before initiating any movement before leaving the stand for departure until reaching our final parking position after landing. The TCAS-part of it will stay OFF until we enter a runway for departure and it will be turned back OFF again when we vacate our landing runway.

 

On VATSIM the general rule is/was to keep transponders on STBY until departing from a runway, turn it off when vacating after landing. Some airports at VATSIM want you to turn your transponder ON at all times, just like in the real world.

 

When flying online I will keep my XPDR on STBY until departure, unless local procedures prefer me operating it ON before AND there is ATC active.

[Brad Littlejohn]

I usually look out on the ground chart for something like:

 

 

And with this, it is going to come down to, at least in the USA, if the airport/ARTCC is simulating ASDE-X. If they are or not, there will usually be a NOTAM about this at that facility's website, if not at least in their ATIS. Some sectors are simulating ASDE-X, while some are not. So this is going to come down to a per airport/per facility basis, and may be better to know this beforehand, or at least inquire on the ground before or immediately after requesting clearance.

 

BL.

[Bradley Grafelman]

Throughout the US, AIM 4-1-20(a)(3) has pretty straightforward guidance:

 

Civil and military aircraft should operate with the transponder in the altitude reporting mode ... at all airports, any time the aircraft is positioned on any portion of an airport movement area. This includes all defined taxiways and runways.

[Robert Shearman Jr]

Throughout the US, AIM 4-1-20(a)(3) has pretty straightforward guidance:

Not to mention VATSIM CoC B4:

Except while on the ground prior to making initial contact with ATC or upon request of ATC, a pilot should not squawk standby. {...}

Perhaps this topic has been flogged to death in another thread, but, I read that as a policy for squawking Mode C as soon as you are on mic requesting clearance. So I'm in the habit of flipping it on as soon as I enter the squawk code. (Unless I forget, which of course never happens. )

[Trent Hopkinson]

And yet when I fly to many countries that aren't the USA, they specifically tell you to squawk standby on the ground.

 

The taxi from the Domestic Terminal at YSSY to the hold-short point at Rwy 34R takes a good 15 to 20 minutes, and I've never been on anything other than Standby till holding short and ready to depart.

[Dace Nicmane]

when I fly to many countries that aren't the USA, they specifically tell you to squawk standby on the ground.

Yup. For example, in Riga, they'll never fail to tell you to squawk standby while taxiing to the gate. In most other places in Europe I taxi to the runway in standby mode and from the runway in mode C (because I forget to switch it off).

[Marcus Haraldsson 1359974]

Once again thanks for the answers!

 

Now, I feel like I've got a mix of different answers.

 

My initial question was regarding EU-OPS, so if I understand it all correctly; in Europe, you operate using ALT RPTG OFF, and in the US you operate with ALT RPTG ON, on the ground?

[Lindsey Wiebe 1101951]

Once again thanks for the answers!

 

Now, I feel like I've got a mix of different answers.

 

My initial question was regarding EU-OPS, so if I understand it all correctly; in Europe, you operate using ALT RPTG OFF, and in the US you operate with ALT RPTG ON, on the ground?

 

There's a mix of answers as that's just the way it is. In RL it's up to the airport to declare they HAVE ground radar and USE transponder on ground in ALT RPTG ON (you wouldn't want TA/RA on as you'd be getting traffic conflicts all around you when taxiing). That being said, we are not RL... If an airport on Vatsim wishes to use it they should put it in their ATIS same as RL. In RL unless you're told (by controller or ATIS) to use ALT RPTG then you don't until cleared for take-off. Obviously a controller can say to use it even if ATIS doesn't mention it... that's up to them, no sweat off our backs as pilots as it's his or her screen that's changing not ours. Sometimes it's also mentioned in the charts (taxi chart for example) so be sure to read the fine print of those as well.

[Marcus Haraldsson 1359974]

Ok, thanks for clarifying!

[Andreas Fuchs]

Hi,

There's a mix of answers as that's just the way it is. In RL it's up to the airport to declare they HAVE ground radar and USE transponder on ground in ALT RPTG ON (you wouldn't want TA/RA on as you'd be getting traffic conflicts all around you when taxiing). That being said, we are not RL... If an airport on Vatsim wishes to use it they should put it in their ATIS same as RL. In RL unless you're told (by controller or ATIS) to use ALT RPTG then you don't until cleared for take-off. Obviously a controller can say to use it even if ATIS doesn't mention it... that's up to them, no sweat off our backs as pilots as it's his or her screen that's changing not ours. Sometimes it's also mentioned in the charts (taxi chart for example) so be sure to read the fine print of those as well.

err, no. As I had explained in my previous post on this thread, in the real world we ALWAYS operate our transponders with ALT ON, but TA/RA OFF until we line up for takeoff. After landing we turn the TCAS OFF ("TA/RA OFF"). Only when we are at our final parking position will we also switch the transponder to STBY. This is done irrespective whether we are at a large airport with ground radar, or not. There is no harm done if the transponder operates on a small field without ground radar.

 

On VATSIM, as explained, it is not that easy. I rather do it the other way around: unless local procedures require the transponder to be in MODE C, I will leave it in STBY until lining up for departure.

[Marcus Haraldsson 1359974]

Ok thanks Andreas.

 

I [Mod - Happy Thoughts]ume you are talking about how it's done in Europe, since that's my original question.

Now, I have seen some pilots in real life apperently putting the transponder to ALT RPTG OFF on the ground so I'm not sure why that is.

[Andreas Fuchs]

In commercial aviation this is now the norm. In my company we operate like this, no matter where we are in the world. It is actually dictated by the manufacturer's pilot operating manual.

[Marcus Haraldsson 1359974]

Ah, ok! Thanks for the information!

 

Just out of curiosity - Is this a relativly new procedure? Since as I said, I've always learnt to put the transponder to ALT OFF on the ground.