FMS usage and applications for ATC purposes

[abrasato]

Hello everybody,
as I am an Air Traffic Controller and I'm now applying on ATC research and development subjects, I need to have a professional consultation with the other side. You, the pilots
In order to better understand the FMS functionalities, I need to know if is possible (or sometimes done) the following action by the pilot:
ATC assigns a specified FL through a clearance (i.e. climb to FL220), the action that I expect to be done by the pilot is -if the read back was correct- (after or at the same time of the readback) the selection on the FMS of this FL (in this case FL220).
Could be possible (and if yes in which cases) that you select another "intermediate FL", even if your intention is to stop the climb at FL220?
I would figure a situation in which you did a correct read back, but you select, instead of FL220, i.e FL260 in order to get, let's say, an higher rate of climb.
I ask you this because the FL you select on board (and thereafter downlinked by Mode S transp) could be useful to understand if you are acting correctly and coherently with the ATC clearance (also when the readback have been done correctly).
Thank you for any contribution.

[vilas]

abrasato
To initiate a climb no action is required on FMS. You set the altitude directly on Flight Control unit and initiate climb and automatic level out at that level.

[abrasato]

And is the FL selected on FCU the FL downlinked by Mode S?

[latetonite]

As I understand, the downlinked info comes from the MCP, but I might be wrong.

The MCP is always controlling, and the FMS cruising altitude, or enroute restrictions would not guarantee you, as a controller, much.

After reading back an ALT clearance, pilots usually set the new alt in the Mode Control Panel, initiate a mode to climb or descent, usual Level Change, (or Flight Level Change in Airbus), or a Vertical Speed ( for small ALT changes), then update-if needed-the FMC.

The FMC(G) is not the primary toy for complying with altitude changes.

It also would not speed up the actions of the airplane, and that is probably what you as ATC is looking for.

Hope this helps.

[737aviator]

On occasion if a departure SID has 'At or Below' altitude restrictions at different waypoints we would select the most restricting altitude in the MCP initially before departure and ensure that the FMS was programmed appropriately for a backup to ensure no level busts. The low level off is selected in the MCP because often its so low that we would reach it before flap retraction is complete and in my aircraft we do not select a FMS controlled climb (VNAV) until NADP is complete.

I usually only encounter this in the Canaries and if a controller clears us to a higher FL than the SID restrictions I would select the cleared FL on the MCP (so the Mode S downlink indicates we've selected the cleared FL), and leave the crossing restrictions in the FMS unless the controller gives us an unrestricted climb. As far as I know the FMS restrictions are not downlinked via ModeS/ADS.

We would never select a higher FL than cleared in the MCP.

[bigduke6]

Possible to do so, yes.
Higher than actually cleared ever set? NO. Never.

If you see higher than cleared on your display from the Mode-S output, then it was a error that I hope someone (you or me) is going to catch prior to the violation being issued!

B744/B748

ATC assigned altitude is set in MCP (mode control panel in Boeing terms). Knob is then pushed (IF level flight/already at a captured altitude) to initiate the climb to the higher level. This then inputs the new level to the FMS.

If I want a faster climb, I can then increase thrust (if using some type of reduced climb thrust was the default/previous setting), or reduce speed to trade some airspeed energy into climb rate if need to for a short time, or to reduce the speed towards best rate of climb speed.

Mode S reads from MCP, not FMS.

If I am cleared to "climb via the SID", then I set the highest altitude on the SID in the MCP and let the FMS do the work of doing the intermediate level off, if there are some. In this case, it ATC will not know from the Mode S that I am going to honor/comply with the level-offs, which is one drawback to the current mode S system.

[Intruder]

Could be possible (and if yes in which cases) that you select another "intermediate FL", even if your intention is to stop the climb at FL220?
I would figure a situation in which you did a correct read back, but you select, instead of FL220, i.e FL260 in order to get, let's say, an higher rate of climb.
I ask you this because the FL you select on board (and thereafter downlinked by Mode S transp) could be useful to understand if you are acting correctly and coherently with the ATC clearance (also when the readback have been done correctly).
In almost all cases (B744 terminology used here), the current "cleared to" altitude is set on the Mode Control Panel (MCP). I cannot think of a good reason to set a higher altitude than the cleared altitude in a climb, or lower than cleared in a descent.

Intermediate restrictions, as on a SID or STAR, are programmed into the FMS via the Control Display Unit (CDU), and are adhered to IF Vertical Navigation (VNAV) is the selected pitch mode. Those intermediate restrictions will NOT be applied if Flight Level Change (FLCH) or Vertical Speed (V/S) is used as the pitch mode. So, even if you have a readout of FMS inputs, you may not be able to tell if the automation is active to honor those restrictions.

In general, VNAV is used in climb and cruise, so all the automated restrictions and protections are applied. Occasionally V/S will be used for a cruise climb to prevent too rapid a climb and the possibility of a TCAS RA. In the descent, however, any of the 3 modes may be used at any given time, depending on the dynamics of the situation.

So, a question back to you: What info does Mode S downlink to ATC other than CURRENT altitude, position, and/or speed?

[Denti]

Position actually doesn't have to be reported, at least for the European implementation of mode s enhanced surveillance. The basic set of informations is call sign, altitude, air/ground status, mode s capability and SI report.

The enhanced part contains quite a bit more information:

Selected altitude, roll angle, true track angle, true track angle rate or true airspeed, ground speed, magnetic heading, IAS/Mach, vertical rate (barometric or baro-inertial).

The big question is though what the ATCO can see, they usually get only a subset of those data sets, the most important ones.

[Bob Lorentz]

abrasato,
I'm interested in what you guys can read from our Xponders in Italy as I am based there.
Just a few days back a Swiss colleague made a mistake and gave us a wrong cleared level (no blame, we're all human). A minute later he/she called us back because he/she noticed that the level we had correctly read back and set was not where we should actually descend to. Great catch by the controller.

[FE Hoppy]

SKYbrary - Mode S (http://www.skybrary.aero/index.php/Mode_S)

The video is very informative for those who haven't received any training recently.

[Chilipepper1]

When a clearance to climb to and maintain FL 220 is received, the FL (220 in this case) is set into the Mode Control Panel (MCP - Boeing phraseology). The altitude button, also located on the MCP is then pushed. If in VNAV, the aircraft will climb more slowly and on profile up to FL 220. More often than not, FL 220 will be set into the MCP and then Flight Level Change (FLCH) will be selected. Boeing programs FLCH, so that the aircraft will attempt to reach the new altitude within two minutes (if possible, which on longer climbs is obviously not). By depressing the Altitude button on the MCP, the revised altitude is automatically introduced into the FMS, requiring less "heads down" time in theory. I never heard of this practice of placing a higher altitude in order to facilitate a faster rate of climb. I've personally never witnessed anybody execute a change in altitude in this manner. I hope that helps.