Setting the throttle when disengaging ATS during final approach

[CargoBull 0]

>> Idle thrust will vary with altitude. The higher you are, the higher "idle" N1 will be.

 

Um.. never thought of that. But if she doesn't let you go below 200 KIAS with N1>40 and refuses to deploy spoilers to calm her down.... quite a challenging landing but in that specific case just the other day I actually made it onto the asphalt in one piece and even got her to stop before the runway was out. Haven't defined failures yet, and nobody gets at my PC to set them behind my back .... I'm a hero ;-)

 

>> Are you sure you aren't disconnecting the A/P, then accidentally reconnecting it with an extra button/key press?

 

Yes I am. The PFD tells me AP OFF in a white frame around the HDG and ALT fields, and I check it all the time for heading, ILS indicators and the tapes, while the SPEED field sports a flashing red frame saying ATS OFF (or similar). Quite annoying. In PMDG options I have "joystick disengages AP" set to "never" so I guess it can't be that it goes on and off depending on my battling the joystick....

 

>> You could try re-calibrating your hardware

Will do. However, with other aircraft all of that does not happen ....

 

>> As long as the plane is within it's normal flight envelope

Good point. Of course I had hoped to have a common problem with a common solution and there was a few plausible hints so thanks for that so far. I might still be a bad pilot that's true and no offense taken. I am a seasoned sim pilot (yes from Apple II days on, with long pauses though) but the MD11X is my first ... well "real" plane if you know what I mean to say by that, and the biggest one for that matter (the default FSX 747 is a toy). I should practice more without any AP and ATS and see what the plane does in reaction to what I do.... *think

[3-2-1-Now 126]

Donut like on 777...Unfortunately not on the MD11.

 

Actually yes there is. It is either over the N1 (GE), or the EPR (PW).

 

"Idle" on the MD11 is like 25% N1 right? Never saw it that low in a descent.

 

You are confusing ground idle with flight idle. Depending on altitude, flight idle is between 35-45% N1.

 

However that could be because, when going manual at the TOD or even earlier, I am too quick with the flaps. I am not a pro so I extend the flaps one more notch whenever I feel that the plane needs my help to decelerate. That way you get slow-flying "powered descents", I know. I suppose what I should rather do, even in manual flight or when flying with manual A/P settings, is follow the pink FMS speeds displayed in the PFD and the proposed flap settings in the speed tape.

 

NEVER use the flaps to decelerate! That is not what they are for. Use the speed brakes. If you plan your descents, she doesn't need any drag (unless ATC screw your plans). If you have a tail wind, tell the FMS in the DESCENT page that it has anti-ice ON. It will move the ToD further away from destination (with anti-ice ON the engine idle is increased, meaning the descent angle is shallower).

 

But if she doesn't let you go below 200 KIAS with N1>40

 

How do you mean? Sounds like the slats are retracted. If you want to decel below ~200 kts, you need to extend the slats, otherwise you'll get into SPEED PROT and the AT will kick in and apply power.

 

and refuses to deploy spoilers to calm her down.... quite a challenging landing

 

That sounds like you have flaps deployed (speedbrake is locked out with flaps selected) if you can't extend the speed brake.

 

If you treat the MD-11 like a supertanker (takes 5 miles to turn, 25 miles to stop) you'll be on the right side of the curve. If you get hot and/or high on approach, you are not going to save it. At MLW it takes 20 nm to go from 315 kts to approach speed IN LEVEL FLIGHT, taking flap on the speeds as she decelerates. Even longer if she has any form of descent rate (>1000 ft/min without speedbrake and you can forget it).

 

I should practice more without any AP and ATS and see what the plane does in reaction to what I do

 

She hand-flies really nicely. Note that the LSAS has an auto-trim function. I found that after takeoff she needs a bit of trim to help her out initially, but after that the LSAS does a great job of trimming (it is a pitch hold function when the control column is neutral in pitch). She also does NOT require back pressure during turns (except initially), so long as you remain inside the roll arc (displayed at the top of the PFD). Note that it is dynamic, depending on speed, altitude, configuration, and phase of flight. The roll arc denotes the operational range of the auto-trim. If you roll outside the arc, auto-trim is suspended until you return inside it.

 

The MD-11 rocks automation. It is very helpful, yet doesn't get in the way of manual operation.

 

Best regards,

Robin.

[Bagman 3]

 

The A/T begins to retard to idle at 50 ft radio altitude I believe. It's always functioned properly for me. 

 

lol I have to try it today then, I've always left the ATS engaged until 100 or 200 ft and have a key assignement to disengage because I didn't know it was like the 777. I don't fly the old lady too often.

[3-2-1-Now 126]

The MD-11 is the MD-11.

 

The auto-thrust is what is called a "full flight" auto-thrust, meaning it can be engaged from takeoff to landing roll-out, regardless of autopilot engagement state. B)

 

Best regards,

Robin.

[CargoBull 0]

Thanks everybody for your patient and helpful advice, some of which I am using below, and a Happy New Year too: The skies is where to go, not the heavens

Apologies for being afk for a while. I was on a holiday and then followed my own advice first and just practiced a bit. As mentioned before, I am more into manual flying - man against machine - than into simulating real-world aviation although you can learn a lot from watching how the autopilot does the job.

On topic: What I do now, if I used the autopilot at all, is setting the throttle lever to the appoximately right position (labelling them helps) in cruise flight, then disconnnect the ATS before the descent and take it from there. That way, there's some margin for error, and flying a curvy descent manually, observing speed and altitude restrictions, is in fact a nice challenge in a big and lazy airliner.

If in PROF and FMS SPEED mode, you can also wait until it goes to idle engines and disconnect then, for an even smoother transition.

A few more observations. More experienced pilots will probably smile at my weak attempts to stay alive at the controls...

# After all those years, I like to think of myself as being quite good at fumbling small and medium (simulated!) planes up to say a 737 down onto the asphalt even after an imperfect approach (= corkscrewing around the glideslope with, well, an improvised speed profile), even in bad weather, but the slow reaction of a big baby like the MD11 takes a lot of foresight and pre-emptive action.

Now, if you approach with AP OFF (pressing Z twice or clicking AUTOFLIGHT twice) and ATS OFF (I programmed SHIFT-R to do that, also press it twice to silence/unblink the warning), and if you then get into trouble staying within or above the glideslope, and/or if your speed drops too low, then some kind of envelope protection kicks in, first wildly blinking the annunciator in the PFD and eventually re-engaging the ATS and giving full throttle, thus forcing a go-around.

You can of course switch it off again, but it will come back on. Sure a good thing in real life, but not with Yours Truly at the wheels. So what I do is push the two big AFS OVRD switches both down, and then it's ME having control. Or what I like to call control. Most any time, I make it down onto the runway with no other damage done than to my nerves.

# If you reduce throttle in level flight, most every plane will start to descend but not the MD11. I guess it's the LSAS that gradually moves up the stabilisers to increase pitch and hold altitude as long as it can, while the plane slows. All of that with AP OFF. Nice to watch that behaviour in PROF & FMS SPEED mode too, e.g. at the T/D.

You then have to actually talk her into the descent. I didn't like that initially but find it helpful now. You can still operate the stabs manually, and the LSAS will take it from there. All of that helps you to quickly find a smooth descent (airspeed and vertical speed each being constant).

# The slower I get, the speed tape tends to oscillate more heavily, and I see erratic appearances of the thin green upward/downward bar that indicates the direction and rate of speed changes. With ATS on, the throttles rock wildly to and fro so you are unable to touch the disengage button with the mouse without pausing the simulator.

@3-2-1NOW, thanks for the many hints from November 23!

> NEVER use the flaps to decelerate! That is not what they are for. Use the speed brakes.

Well but the flaps DO decelerate the plane don't they... and the lift effect of extracting the flaps is dramatic in manual flight, especially from slats out/flaps zero to flaps 15. I do that as early as I can to have as much margin as possible to manage the effects of the additional lift and drag.

> She also does NOT require back pressure during turns

Can't confirm that fully although LSAS indeed seems to be helpful. Also, coming out of the turn, you have to push too to hold altitude, like in every other plane.
 

[mburkhard 23]

Well but the flaps DO decelerate the plane don't they... 

 

Yes and no, they do increase drag but at the same time create LOTS of lift. And how do you kill lift? Indeed, by lowering the nose, but what happens usually if you lower the nose... yes, speed rises. So there you go... Might be ok in level flight, but then you wouldn't have trouble decelerating in level flight would you.

So yeah flaps are indeed  not meant to be used to decelerate

 

 

 

Real flight manuals don't help here of course. How do you handle this? Other than not switching it off?

 

Why don't you just remember the N1 or EPR setting before you switch ATS off? That way you can re-adjust the engines quickly to whatever it was. Yes it is not quite as easy as on the real aircraft, but still it works and it is always a good idea to know your thrust setting required for that 3° descent with Vapp.

And if ATS is struggling to keep the setting while you do switch off, then you'll have to do same anyway and it won't really matter where your hardware throttles are set.

 

 

Why? I always disengage it.

 

If you want to disable LSAS during approach do NOT use the override switches or the LSAS buttons on the overhead. Use ONLY the yoke's AP disconnect button and keep it pressed. That is the only way it is meant to be and is perfectly safe to do. As soon as you release the button LSAS will work again.

 

 

Cheers,

Markus

[CargoBull 0]

@Markus

See what you mean and you got a point there. We agree that the flaps are meant to enable you to fly slow, never mind how you manage to decelerate to that desired slower speed.

 

>> (the flaps) increase drag but at the same time create LOTS of lift.

 

... and thus slowing you down even more, beyond the additional drag. To prevent that, and to stay reasonably near the desired descent angle, I tend to push the yoke right into the initial effects of a new flaps setting. That's to keep the nose steady where it was. That way, the additional drag does part of the job of slowing me down. And I am pretty sure that I see the PROF and APP modes do the same thing when I "disturb their circles" with extracting the flaps.

[mosteen 111]

If you want to disable LSAS during approach do NOT use the override switches or the LSAS buttons on the overhead. Use ONLY the yoke's AP disconnect button and keep it pressed. That is the only way it is meant to be and is perfectly safe to do. As soon as you release the button LSAS will work again.

 

 

Cheers,

Markus

Hello Markus, this I did not know to be a function, very interesting.

 

Do you know what type of rw scenario would call for an intermediate disabling of the LSAS during approach?

 

Never heard or read about this before, neither was it mentioned when I flew Lufthansa's MD11 simulator in Frankfurt.

 

Cheers,

[mburkhard 23]

Morten,

 

as I understand it, this function is not / was not widely used by MD-11 pilots. Personally I've heard of only one pilot telling me he would do that from time to time when being on final approach in turbulent weather. I guess it's a matter of personal taste and not something an airline would write into their SOPs...

 

Cheers,

Markus

[mosteen 111]

Rgr, many thanks Markus, I have it on my list, I'll be testing it together with varying the sensitivity setting to see if I can find a good spot. With ASN it opens up for some interesting and lively approaches

 

Cheers,