ATC Altitude Readout
 

On another forum, it was suggested that ATC can "see" the altitude set on the MCP. Now, of course they get that info via the transpoder, mode C but I've never heard that what is set on the MCP is also transmitted! Can anyone enlighten me?

yeah we get the EMS data that displays the Final State Selected Altitude (or whatever the manufacturer/operator equivalent language is).

Makes it easy to catch mistakes and such - if after 5 seconds the level we enter in the label doesn't correspond to the MCP level, the "cleared level"field in the label flashes yellow.

They also get the speed set on the MCP. If ATC says to slow to 230 and minimum clean is 232 many pilots used to set 232, figuring a few knots would not matter. Now ATC (in some areas) can see you're cheatting.

And would hopefully realise why and not complain about 2kts or even mention it. If your in Australia, 2kts is far more significant so should expect a report to be filed regarding you breaching their instruction.

In my wildest dreams I can't imagine taking a crew to task for a 2kt discrepancy!

You aren't an Aussie then.

As far as i know they only see the actual IAS, not the set one. Might be a difference between Mode S Enhanced Surveillance (Europe) and ADS-B (elsewhere) though.

Correct, IAS is part of the EHS spec (and there's provision for it in the ADS-B spec as well, though I've never seen it used in a squitter).

Selected Speed isn't in the EHS or ADS-B specs.

This is nonsense up with which I cannot put. ATC's job is to separate traffic, NOT monitor my job which is to fly the plane. Are they down there BECAUSE I'm up here or is it the other way 'round? If I'm 2 knots fast, it's for a reason, now make an adjustment.

The other limitation is that ATC cannot see if there is an FMS vertical conditional limitation; take the DVR8M departure out of EGKK26L, there are three vertical requirements: Below 4000 @ 29DET, 5000 @ ACORN and 6000 @ 33DVR. With managed climb the final 'stop alt' of 6000 can be set and the auto flight will comply with the vertical constraints by going ALT CST*. I know airmanship, etc, may dictate that you don't trust the FMS vertical protection and incrementally set the altitude restrictions as you pass them, but after all, this is how the Airbus is designed. The problem is on Mode S, ATC has a canary when he sees the 6000 set on the FCU without being privy to the intermediate levels in the FMS route.

TOD,

Exactly.

Are you saying that ATC will explicitly query the FCU Selected Altitude setting with the pilot if it doesn't correspond to the intermediate restrictions on the SID ?

Hi Dave, had direct experience of this myself August 2014.

ATC's reaction will partly depend on how they are recording the clearances they have issued.

In the Gatwick SID example London TMA controllers are still using paper strips. In most cases they won't check the Mode S unless they have a particular need to do it. Frankly they are usually too busy to worry about checking everything the pilot does beyond the traditional read back.

In other cases, such as Maastricht, the controller will enter clearances directly to the system which will then monitor the Mode S/FCU data and produce an automatic alert if there is a discrepancy between the two. i.e controller clears FL330 - pilot enters FL350.

The tolerance I was taught, and work to, is +/- 10 Knots. I could see you getting upset about someone bitching about +/-2 Knots.

However, if you have been asked to fly a speed and are still 20 or 30 knots adrift after a reasonable time to comply, you will have to put up with my nonsense. My job of separating aircraft depends on the pilot doing his job of flying the plane as he is instructed to. If he can't or won't, my monitoring that non compliance and recognition that the actions of that pilot will erode separation will cause me to take action.

I'm down here because the people down the back are paying your wages and mine :}

Mode S enhanced squiter:
1) Mode A Code
2) Pressure altitude
3) On-the-ground status
4) Aircraft Identification
5) Special Position Indication (IDENT)
6) Emergency status
7) Data link capability report
8) GICB capability report;
9) ICAO 24-bit aircraft address; and
10) ACAS active resolution advisory report.
+
(a) MCP/FCU Selected Altitude;
(b) Roll Angle;
(c) True Track Angle;
(d) Ground Speed;
(e) Magnetic Heading;
(f) Indicated Airspeed or Mach No ;
(g) Vertical rate:
(h) Barometric Pressure Setting
(i) Track Angle Rate or True Airspeed

Exactly how much of that is received depends on aircraft and ground equipment.

Mode S EHS (EnHanced Surveillance) isn't a squitter (ie sent, unsolicited, at regular intervals).

It's a response to an ATC interrogation (like Mode A/C), although some of the content (groundspeed, track, ACID, etc) duplicates what's in the ADS-B 1090 Extended Squitter (ES).

Just the other day on a STAR into London, the controller gave us a speed restriction of 230KTS. They then queried the aircraft in front of us by saying BLABLA we gave you a restriction of 230 KTS, we can see your IAS is 224KTS? Maintain 230KTS and contact london on ....... They then said to us BLABLA we gave you a restriction of 230KTS, we can see you IAS is 232KTS, maintain 230KTS contact london on .....
After we had finished laughing we contacted the new frequency to be met by much giggling....I can only assume they were having a laugh at us!!


Thank you for the correction, how did that happen!

@DaveReidUK

Quite correct. My bad, I was in a rush.

into or out of? :confused: