ATC IssuesA place where pilots may enter the 'lions den' that is Air Traffic Control in complete safety and find out the answers to all those obscure topics which you always wanted to know the answer to but were afraid to ask.
Someone told me that the controllers know only the ground speed of the aircraft not IAS. The others said that the controllers know whatever we ,pilot, set in the cockpit such as altitude,heading or speed. What is the truth sir?
Controllers are only presented with ground speed on a surveillance display. That is what they and aircrew use for time/distance. To know what airspeed is they would need a readout from the acft ASI. They may, for instance, ask for the acft IAS when applying speed control between acft. E.g. when one acft is following another, they may request the IAS of the lead aircraft and then instruct the following acft to fly at, or not above, that speed to maintain separation.
It all depends on the system in use. We receive mode S data and see the callsign which has been input, the selected Flight level, Mach No. Magnetic heading and the IAS The selected flight level is very useful and has stopped a few level busts !! Although some pilots can be very surprised when they realise what information we can see. Apparently a lot more information is downlinked, but is not shown to us lowly controllers
Location: The Peoples Alcoholic Republic of Jockistan
Posts: 1,334
If we open another box, further Mode S information available is the Rate of Climb/Descent, aircraft identification (input by the pilot or hard coded in Mode S transponder), and the Mode S hex code.
__________________
10 West
UK ATC'er Old enough to know better, young enough to carry on regardless.
Anyone with a bit of experience can give a fair guestimate of ROC/ROD from the mode C and of the TAS from the groundspeed, along with the known winds and observed speed of other traffic.
e.g. if you claim to be doing the same 200 kts as all the other traffic at the same altitude, in the same direction but indicate 40kts faster - someone's telling porkies!
AC Swanwick (UK) don't have full Mode S interrogation yet, only selected flight level, however the implementation of the rest of the info my colleagues mention above is imminent.
If we open another box, further Mode S information available is the Rate of Climb/Descent, aircraft identification (input by the pilot or hard coded in Mode S transponder), and the Mode S hex code.
ROC/ROD is only sent by aircraft fitted with ADS-B, which includes most, but by no means all, Mode S-equipped airliners.
Among the exceptions are MD-80s, CRJs, ERJ-145s, etc.
ROC/ROD is only sent by aircraft fitted with ADS-B, which includes most, but by no means all, Mode S-equipped airliners.
Among the exceptions are MD-80s, CRJs, ERJ-145s, etc.
I doubt this is true, but I can't confirm it. We get ROC/ROD from all MODE S readouts if we get anything at all. I doubt that they are all ADSB equipped, but perhaps they are.
Of what practical use would the controller make of IAS anyway ?
To make sure those pesky pilots are flying the speeds we tell them to fly!!
"We're 220kts" - No you're not. You're reducing through 310kts
"We're 180kts" - No you're not. You're back at 160kts and about to have matey boy behind you up your chuff
"160kts to 4 DME" - Why are you slowing down at 7DME then?
the QNH set in the cockpit in TC (Although for some aircraft types, it doesn't always work properly)
I've noticed this too but have never been given a reason for it. Best guess from me is that the certain aircraft types have a 'standard pressure' button when above transition, and then they turn it off for below that, so they never actually change the QNH pressure setting until arrival. Might explain why the downlinked pressure is wrong (and probably dep qnh, I should check this at some point when quiet!)
as for
Quote:
[Of what practical use would the controller make of IAS anyway ?
Very handy on windy days when two inbounds from different directions are going to get fairly close at a common point, it leads to much more efficient streaming, especially if neither is yet in your sector.
I doubt this is true, but I can't confirm it. We get ROC/ROD from all MODE S readouts if we get anything at all. I doubt that they are all ADSB equipped, but perhaps they are.
If you are seeing ROC/ROD for aircraft not equipped with ADS-B, such as the types I listed, then it's being computed from successive DF4 (altitude interrogation) Mode S responses. In the absence of ADS-B, there is no provision for the aircraft to send explicit vertical rate information.
Location: In some hotel downroute or in some hotel doing union negotiations.
Posts: 2,371
Mode-S enhanced surveillance is not ADS-B (albeit kinda close to it) but requires downlinked rates of climb/descend (BDS 6,0). Enhanced surveillance is by now required in many ECAC states. According to the aircraft list on the eurocontrol site recent MD-80s can downlink rates of climb/descend, just not selected altitude. CRJs can downlink rates as well, just not track angle rates. And EMB-145 can downlink all required parameters as standard. Retrofit kits exist to make those airplanes fully EHS compliant and many operators have fitted them as it is easier than to get an excemption from EHS from each individual state within europe.
