Strange behaviour descending into OMDB following STAR

[Jd_jay 4]

Hi guys, im not qualified to call this a bug or anything like that but i feel their was a bit of a problem descending into Dubai.  I was flying the 400F Cargolux livery from EGSS to OMDB.  Everything went brilliantly the whole flight until this point, ive not seen this behaviour following this STAR before. STAR DESD1C for 30R, basically what happened was i was descending nicely and as planned, waypoint ULASO calls for you to be at 6000 or above, which the aircraft did, but on passing that, it descended down to 3000 quickly, which is what i set in the MCP ready to pick up the glide slope prior to T/D.  As you can see from the FMC legs page and the vertical path deviation indicator on the ND this should not of happened, it should of been more gradual.  I have enclosed a couple of screen shots to show all this and my MCP settings. any advice  would be great, i have done this approach a few time in the 777 and that has never happened before.

 

 

 

 

 

 

 

[pcubine 143]

any advice would be great

Better than the three screenshots shown would be one that showed what your FMA/MCP were during the descent from 6000 to 3000. It looks like you clicked on the speed knob otherwise 210 kts. would not be showing in the window. If you decreased the speed from whatever was on the CDU the airplane will increase the descent rate and no longer stay on profile. If I click on the speed knob I usually go to V/S rather than staying in VNAV. I try to stay on profile by varying V/S. Why this happens was explained to me during beta testing but I didn't understand it then and I don't understand it now.

[Jd_jay 4]

Nothing was any different on the MCP, i may of mucked up, waypoint ULASO also calls for a speed restriction of 210knts, as i was approaching ULASO the aircraft did not start to slow down to 210knts so i intervened as i thought that was the point i had to start slowing the aircraft down manually, maybe that was not the case but why did it not slow down automatically as it was showing 210/6000A on the FMC

[pcubine 143]

why did it not slow down automatically as it was showing 210/6000A on the FMC

If the airplane had not reached the green circle prior to the waypoint with the 210/6000A, it will not slow down. Prior to reaching that circle you will need to extend the flaps so that the airplane can safely fly at the lower speed otherwise the airplane will not reduce speed.