Mode-S data

[squawkident.]

Hi

Was having a discussion with a few colleagues about what data an ATCO can see with regards to an aircrafts selected FCU or FMC panels.
I'm an airbus pilot for a large LOCO and was wondering exactly what data is transmitted to ATC.

My understanding is ATC can see selected speed, HDG and selected FL/ALT - is this true?
Finally, i've had a few TCAS TA's in the past week and was wondering whether ATC were alerted to a TA at the same time we were or whether you used a different alerting system?

Thanks guys

[ToweringCu]

Actual airspeed, ground speed, heading (not track), selected FL/alt. Any, all or none of the first three can be chosen for display, selected FL is always displayed. Our collision warning is derived from the radar display and is independant from TCASII. I'm sure some ATC equipment may differ.

[kme]

For the moment it is a big discrepancy between what is possible and what is actually seen. The Mode S implementation on the ATC side is far from finished and it depends very much which center/airport you talk about. Specially since most countries have differing (their own) ATC systems still...

When it comes to enhanced mode S downlink parmeters (the speed, level, heading) its just about only London that have access and soon Maastricht. (Feel free to correct me if im wrong it might be that my knowledge is not up to date.) The exact parameters seen will likely depend on the implementation - some may see more than others even after the implementation is done. (since this is likely system dependent and of course limited by the standardised airborne capabilities)

TAs has as far as i know never been a suggested downlink parameter, a big discussion about the pros and cons about RA downlink is still ongoing but to my limited knowledge no one has this ability yet.

As for warning systems i would assume that most radar equipped european ATC providers are using some kind of Short Term Conflict Alert (STCA). This provides roughly 2 min prewarning before a loss of separation. The TCAS doesnt care about separation and have in cases even contributed to losses of separation - its the last system in the safety net and just aims to miss...

My 2 cents...

Edit: The STCA is radar derived and not affected by airborne equipment.

[kme]

looks like Scottish is already making me outdated...

[coracle]

Good evening Squawkident.

In the London TMA the actual IAS, ground speed and heading can be selected for display, with the selected flight level being always displayed. We can also get the rate of climb/descent displayed as well, but this is a bit of a faff!!

As regards to TA/RA's, we have 2 stages of Short Term Conflict Alert which is derived by the radar processer. The first stage is where the aircraft which the computer judges that there may be a problem, the aircraft concerened flash white. We're told that it is roughly the time that you'd be getting a TA in the cockpit. The second stage is where the computer judges that there is a serious problem i.e separation has been lost and the aircraft concerned flash red. Again we're told that you'd be getting an RA.

From your post I assume that you fly into and out of Stansted or Luton. I guess most of your TA's are either in the BPK area when inbound, or when you climb to Flight Level's beneath the Heathrow stacks when outbound. When you're inbound, we tend to climb the Heathrow departures to FL110 against the SS/GW inbound we have dropped to FL120. If the outbound has a high R.O.C. then we get the white flash as the a/c passes about FL90 which I guess is when you get a TA. Likewise, when you get climbed from altitudes to flight levels ie FL70 if the pressure is 1013mb or above, if the R.O.C. is judged by the computer that it may cause a problem at BNN or LAM we again get the white flash and you the TA.

Hope this helps and as always you are more than welcome to come and visit us in sunny Southampton!

[Radarspod]

In the London TMA

And Manchester, and come December, Scottish FIR :ok:

All TCAS II RAs are broadcast downlinked (BDS 3,0) by all Mode S capable ground radars while the RA is active. This is an ICAO Annex 10 requirement for the radar system.

At this point in time I believe that Luxembourg :confused: is the only European country displaying TCAS RA information to controllers, although many ANSPs are considering it - but is difficult regarding agreement on what benefit it would give a controller knowing an RA is going on against the level of nuisance alerts. And anyway, if its a genuine TCAS RA due to a proximity situation, it is mostly a bit late for the controller to get involved anyway!

RS

[Weirdo Earthtorch]

Mode S (http://www.levelbust.com/articles/mode_s.htm)

Not stated in the link above is the 'same vertical intent' warning - where two aircraft populated to the VSL show conflicting SFLs - can be quite useful if someone drops a goolie.

[squawkident.]

wow thanks very much for all your quick replies.

Much appreciated

SI.

[chevvron]

Bear in mind it's only ATCCs which can see mode S info; airfields such as Humberside , Blackpool etc don't have the software.

[A I]

There's an Eastern European state downloading and displaying TCAS RAs using Mode S. It might be Prague or maybe Budapest.

A I

[kme]

The time for the actual RA to be displayed to the controller has to be relatively small for the function to be able to give any benefit except for statistical use.

In general my impression (theoretical - not hands on) of the mode S downlink reaction time is that it is to slow to be of any direct use. Lets say RA protection give 30 sec prewarning, with 20 sec assumed time before display to controller this leaves about 10 sec for contoller to notice and think of his options and act (reads basically - nonoptions/not act)

This is simply not anywhere near what is needed to be able to sort out a situation - it can take 30 sec to get a word in on a busy freq even for the controller (bad case ok but anyway). Then consider that the controllers controlling-role is more or less over the second the RA comes into play.

I remain to be convinced of the use of this except as for statistical and investigation info.

[A I]

Hi kme,

You have explained exactly why there is a reluctance for most European states to use Mode S datalink for this purpose. Unfortunately there is political pressure for a solution to this as, I believe, display of RAs was a recommendation post Uberlingen.

[AlexCartman]

It really depends on the ATC system what data is being displayed (or at least available for display) to the controller. At my facility I get to see nothing except flight ID, and even that only for flights that the system recognises.