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I have flown with a few captains that have told me that air traffic control can see the settings we set on the FCU (or MCP on B737): enter image description here

Is this actually correct? I'm aware that ATC can see what speed, heading, altitude, V/S, etc. we're actually flying, but can they see what we have selected on the control panel?

I'm not sure if it makes a difference, but I am in Europe.

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  • $\begingroup$ In the U.S. ATC (controllers) cannot see what has been selected on the FCU/MCP. ATC can see the effects of what was selected (e.g., climb/descent, heading) as you have pointed out. – $\endgroup$
    – user22445
    May 16, 2022 at 15:35
  • $\begingroup$ Related: What is the purpose of the selected altitude/airspeed in ARINC 429? In Europe as asked, seems so at least for certain selections/airplanes, but more details are needed, so thanks for asking this. $\endgroup$
    – user14897
    May 16, 2022 at 15:41
  • $\begingroup$ ATC can see Selected altitude, true airspeed, Mach, indicated airspeed, track angle rate, true track angle etc on aircraft lable if the automation system (radrar) is Mose S enabled. In India, we can see these data and it seems Europe too can see Selected altitude and provide alerts when there is a mismatch between cockpit selected altitude and cleared altitude $\endgroup$ May 17, 2022 at 0:52

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Apparently they can if the ATC facility supports Mode-S EHS transponders. According to the linked Skybrary article

Aircraft compliant with Mode S EHS provide ELS functionality features (see above) plus some or all of the following downlinked aircraft parameters (DAPs):

  • Selected Altitude - the flight level which is manually entered in the FMS by the pilot[...]

Emphasis on the FMS is mine as the altitude selected on the MCP does not necessarily match the altitude selected on the FMS. For the sake of completeness, Mode-S EHS also provides:

  • Roll Angle, True Track Angle and Track Angle Rate
  • Ground Speed
  • Magnetic Heading
  • Indicated airspeed (IAS) and Mach-number
  • Vertical rate (barometric rate of climb / descent)
  • TCAS downlinked resolution advisories

But for more details on each of the bullets I would strongly suggest that you read the article. You will see for example that the selected altitude or the roll angle will most probably be used by the algorithms backing the system and not by the controllers themselves.

A small note on this one though:

I'm aware that ATC can see what speed, heading, altitude, V/S

All the above (with the exception of altitude) are calculated with the available ground equipment and are not based on the aircraft readings. From the altitude, the radar system has to deduce the vertical speed. And there is some terrible rounding taking place as the accuracy of Mode-C is 100 feet. So if you have a radar scanning at 5 seconds period, an aircraft with a low RoCD (less than 1200 fpm in that case*) might appear as maintaining the altitude between 2 subsequent scans while it's actually descending. All I'm saying is that (with the exception of the altitude) the rest are as good as the ground system processing them. Mode-S is meant to change that but this is still work in progress as far as I know.


*That might need a bit of an elaboration:

60 seconds / 5 seconds = 12 scans per minute times 100 equals 1200fpm the vertical "resolution" of the radar. What I am not taking into consideration is the Mode-C rounding and the case of having double (or triple) radar coverage and in that case the radars most probably will illuminate the track at a different time. As I am not a radar expert though, I can't provide any more details and 1200 might be an exaggeration while 600 might be a more certain value. I know though for sure from people who worked on these systems, that back then when they designing the system, V/S computation from Mode-C was a challenging aspect.

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  • $\begingroup$ Most air transports built within the last 20 years give or take are EHS-capable. Older aircraft may have EHS-capable Mode S transponders (due to common spare parts pool) but will be EHS-capable only if they've had the necessary wiring changes to get the parameters to the transponder. Many have been retrofitted, but there may be some that have not. I believe there are places that require EHS to operate in their airspace. $\endgroup$
    – Gerry
    May 17, 2022 at 21:13

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