• FMC vertical and speed profiles not recalculating for manually entered SPD/ALT constraints

    • Status: Pending

      717 Version:

      MCDU Report Category: Function Related

      Departure Airport (ICAO): EDDH

      Arrival Airport (ICAO): EDDF

      Departure Runway: 15

      Arrival Approach and Runway: KERAX25S, ILS Z 25L


      Current Leg: PIROT

      Cost Index: 100

      Cruise Flight Level: 300

      Zero Fuel Weight: 76400

      Gross Weight: 86000

      Minidump: https://forums.tfdidesign.com/uploads/

    Flight Sim Platform: Prepar3D v4

    Brief: When manually entering speed or altitude constraints on the MCDU ACT F-PLN page, the vertical and speed profiles are not re-calculated. The entered constraints are not respected by the autopilot.

    How to recreate:

    1. Start off with a new flight and load the "Ready To Start" panel state
    2. Load the aircraft with 9598lbs of fuel, 34 pax and 1250lbs of cargo
    3. On the CAPT MCDU, open the F-PLN INIT 1/3 page
      1. Enter "EDDH/EDDF" into the FROM/TO field
        1. (no company route found)
        2. Select "RETURN TO F-PLN INIT"
      2. Enter "300" into the CRZ LEVELS field
      3. Enter "100" into the CI field
    4. Switch to WEIGHT INIT 2/3 page
      1. Enter "9.6" (10^3 lbs) into the BLOCK field
      2. Enter "86.0" into the TOGW field
      3. Enter "22.4" into the TOCG field
      4. Enter "19.2" into the ZFWCG field
    5. Open the ACT F-PLN page
      1. Select EDDH
        1. Select SID
          1. Select "15" from the RWYS list
          2. Select "IDEK6D" from the STD SIDS list
          3. Select "INSERT"
      2. Select IDEKO
        1. Select AIRWAYS
          1. Enter VIA "Y900" TO "TIMEN"
          2. Enter VIA "UL126" TO "PIROT"
          3. Select "INSERT"
      3. Scroll down to waypoint PIROT
        1. Enter "/23000" into the scratchpad
        2. Press the right hand LSK next to PIROT
        3. Select "DES"
      4. Select PIROT
        1. Select AIRWAYS
          1. Enter VIA "T152" TO "KERAX"
          2. Select "INSERT"
      5. Scroll down to waypoint ROBAR (directly after PIROT, distance 23NM)
        1. Here you can see the first issue (see attached image): The altitude prediction for waypoint ROBAR is displayed as "FL300" in small print. I expected the FMS to recalculate the descent path (since "DES" was selected earlier), to reach FL230 at PIROT and maintain the altitude constraint (FL230) afterwards.
          The same applies when altitude constraints are added mid-flight, with the complete routing to EDDF (including transition and approach) set up in the FMC.
        2. Press the right hand LSK next to ROBAR (empty scratchpad) to open the VERT REV AT ROBAR page
        3. Enter "280" into the SPD: AT/BELOW field
        4. Select "RETURN TO ACT F-PLN"
      6. Scroll down to to waypoint EMBAD (directly after ROBAR, distance 24NM)
        1. Here you can see the second issue (see attached image): The speed prediction for waypoint EMBAD is displayed as "300". Again, the FMS should recalculate the speed profile to maintain the last  constraint (280).
          The same applies when entering a speed constraint mid-flight.

    During flight, the Autopilot ignores the manually entered altitude constraint: PFD displays "PROF TO 23000", but the magenta circle stays at 30000ft even when passing PIROT.

    Related reports:

    • "Altitude Restrictions Not Recalculating TOD or Profile", posted May 9th 2017, concerning Version
    • "MCDU: Re-calculate TOC/TOD", posted July 18th 2017

    I hope this is helpful.


    User Feedback

    Recommended Comments

    Good news - this issue seems to be fixed as of!

    Note for pilots experiencing a similar issue in

    There is no warning displayed on the MCDU if the entered constraint is in conflict with another one down the line; for example:

    • Waypoint 1: ALT constraint "FL90 or above"
    • Waypoint 2: no constraints, expected FL93
    • ...
    • Waypoint 6: ALT constraint "6000ft or above"

    If you edit Waypoint 1, and enter a new ALT constraint that is lower than Waypoint 6's, it will be ignored:

    • Waypoint 1: ALT constraint now "at 4000ft"
    • Waypoint 2: no constraints, but expected FL is still FL93! The Aircraft would have to climb again to comply with Waypoint 6's ALT constraint, if it were to descend to 4000ft at Waypont 1!
    • Waypoint 6: ALT constraint "6000ft or above".

    Not sure if this is consistent with real MCDU functionality, but certainly something to look out for.


    Share this comment

    Link to comment
    Share on other sites

    Join the conversation

    You can post now and register later. If you have an account, sign in now to post with your account.
    Note: Your post will require moderator approval before it will be visible.

    Add a comment...

    ×   Pasted as rich text.   Paste as plain text instead

      Only 75 emoji are allowed.

    ×   Your link has been automatically embedded.   Display as a link instead

    ×   Your previous content has been restored.   Clear editor

    ×   You cannot paste images directly. Upload or insert images from URL.