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ahinterl

MD-11 (FS9): Slowdown on descend

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I've flown several automatic descends with different results, so I thought I better ask here (I've probably missed this in the manuals).I'm somehow confused about the way the FMS determines target speeds during descend and approach, and I'd like to get a clarification on the magenta circles (hollow, filled) on the speed tape:I've experienced that the target speed isn't necessarily the speed present in the FMC. E.g. I had a situation where the next waypoint during descend was listed with 190 in the FMC, but the plane continued to sink with 240 kts. At some point, there was a speed reduction commanded, but again, the 190 wasn't the target speed.So, when does the FMS target what speed?When doing these speed reductions, a filled magenta circle is present at the respective speed on the speedtape. Not so when there's a need for flaps to be set to continue the slowdown: In that event, a hollow magenta circle is present at the planned target speed additionally to the filled magenta circle. That hollow circle gets filled and chased by the FMS only when the next higher flaps setting is selected.When does the FMS transition from "normal" descend slowdown to "flaps driven" slowdown?I had several situations where the automatic slowdown was unreliable or not even performed. How can I best proceed in such situations i.e. how can I determine my energy management wouldn't get out of bounds during descend/approach? Is it sufficient to follow planned speed targets on the FMC? When can I tell whether automatic slowdown is going to fail and react early enough without running into a situation where I discover a failing automatic slowdown too late and cannot perform a proper descend/approach anymore because speed would be too high?Thank you in advance for your answers.Andreas

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The 190 kt speed constraint was probably below min clean maneuvering speed, so the FMS cannot slow to that until the flaps are out.The circles on the speed tape indicate system target speeds when different from commanded speeds, such as when using FCP SPD or if target is in the flaps range.Note the airspeeds on the LDG INIT page. Use those to anticipate when to put slats out (I usually have slats out a few miles before I anticipate needing F15), and when to start your flap deployment. She will slow automatically regardless of speed constraints on flap deployment. I usually find that slats below 230 (depending on weight) puts me at a speed where I don't slow to initial approach speeds until F28 and I am dropping gear, about 3-5 nm before final course intercept. Once you get used to her, she does descents and speed management very well.

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Thank you, Dan, for the informations. Some comments from me though:

The 190 kt speed constraint was probably below min clean maneuvering speed, so the FMS cannot slow to that until the flaps are out.
The interesting thing is: The plane descends e.g. with 240, the predicted speed for the wpt ahead in the FMC is 190, and then all of a sudden the filled magenta circle is relocated to e.g. 220 and the aircraft decelerates. I think I can remember the 190 having been above the yellow area on the speedtape. If 190 was too low, wha was a very different speed selected automatically?
The 190 kt speed constraint was probably below min clean maneuvering speed
I must have missed this completely: What indicates the minimum clean maneuvering speed? The start of the yellow speed band?
The circles on the speed tape indicate system target speeds when different from commanded speeds, such as when using FCP SPD or if target is in the flaps range.
To be more precise here: I guess I understand what the circles mean. What I'm somehow puzzled is that during descend, the FMS constantly commands lower speeds and the filled magenta circle is set accordingly - until a certain point when another, hollow magenta circle appears in addition to the filled one.So, there's a transition from the "normal" deceleration to a kind of "planned" deceleration where deceleration would take place only when flaps are extended further. Before that point, this behaviour didn't exist, the plane decelerated automatically.I now wonder what this special point is when the transition to the "flaps based deceleration" occurs and from what it depends (altitude, speed).
She will slow automatically regardless of speed constraints on flap deployment.
Good to know, thank you.I'll experiment some further to see whether I can anticipate the points where deceleration should occur and thus determine whether automatics are still doing right or I need to respond manually.A big concern of mine is that the automatics don't do what i expect and I see this too late. So, I like to find a way that puts me in a position where I can tell whether this occurs at all. Sometimes I manage that my planes don't do what I want and often things get out of control, so I'm watching constantly and am prepared for a manual takeover. The A/P and A/T off switches have always been special friends of mine :( Andreas

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Try a standard arrival pattern with a downwind, base and final legs. Deploy slats on downwind, F15 on base and turning final drop gear and F28. Plan to be in landing configuration when you pass the FAF (F35 or F50). The speeds will vary based on weight.

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