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Guest Darren Howie

FLCH question.

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Guest Darren Howie

Ok a question for those with more 744 knowledge than myself.Is FLCH the same on the 744 as the 76??Reason why i ask is at the moment with the queen if i use FLCH and increase the speed by more than around 15kts instead of the aircrfat pitching down and increasing the ROD to pick up the new speed the thrust is coming up as well.IN FLCH on the 76 FLCH engages thrust hold at idle and pitches down to increase the speed.This is an integral part of energy management when operating into airports with steep CTA steps.IE rolling the speed back then using FLCH to effectively dive the aircrfat to a lower level with a far higher ROD than if you maintained a steady say 250kts.At the moment when in the 744 as i said above the thrust is chipping in and hence it is not possible to get the high ROD's required to use this technique.SO is anyone else seeing this and or is FLCH in the 744 not a thrust hold function at idle and speed is controlled with pitch??CheersDarren

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Guest Darren Howie

As a further note anyone wishing to see how FLCH "may" be bisbehaving do this.Set the aircraft up at 9000' at 220IAS.Set say 5000' engage FLCH and wind the speed to 270IAS.In real life if FLCH should be a thrust hold function with idle thrust the aircraft should pitch down while maintaing idle thrust to descend at 270IAS to 5000'.At the moment the queen descends but thrust is spooling up to assist in bringing the speed up to 270 then returnng to idle once 270 is near to being obtained.SO my question is is anyone else seeing this and is it accurate for a 400???Operating in a country which has steep CTA steps energy juggling is a tool we use every day on the A320 and every other commercial jet.Its one this FS does not simulate at all and something you can do to increase the realism of your simming.In Aus CTA limits are normally not below 9000' till 30nm then 5000' till 20nm and 3000 till 10nm.Try that in a fully MLW 744 and see how you go.In the 30 we need full speedbrake for at least 15nm from 30-15 when landing in excess of 63T.In the real world we roll the speed back to 220 or so just prior to hitting the 9000 step and then use FLCH(open descent on the airbus its the same thing)to spear down to 5000 accelerating to 250 IAS.ROD's up around 3000'/min are seen as the aeroplane descends to accelerate.Hence no profile or excess use of speedbrake required.Makes for good fun.Darren

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Guest D17S

FLCH isn't a speed change mode. It's a constant speed (speed on pitch) altitude change mode. Here's what happens on the 747-400 (from an earlier post)."The first thing to note is that FLCH SPD

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Darren, you may have to refer to your own airline's tech experts for specific details regarding FLCH (preferably Boeing or RockwellCollins). The manuals I have do not go into enough detail in this regard during descent.A few years ago, I came across the term "Intelligent FLCH". I believe it refers to the modifications made to FLCH mode which allowed for less than max climb thrust for small altitude changes (for pax comfort). With this intelligent system, the aircraft tries to reach the new altitude within about _2 minutes_. If you are making small altitude changes, say, 2000', then Intelligent FLCH will give you enough thrust to attain a climb rate of 1000'/min (i.e. 2000' in 2 minutes). Obviously, for large altitude changes, you are not going to achieve your target altitude within 2 minutes, so the A/T will simply give you full climb thrust.Whether the 2 minute target applies to descents, I am not sure. E.g. in your scenario, if you are making a large altitude change, then the aircraft should pitch down if you dial in a higher airspeed. With a small altitude change, IF the 2minute logic applies to descents in PMDG, perhaps the A/T is coming out of idle and adding thrust to slow the descent rate to achieve the altitude change within 2 minutes (rather than sooner).The 2 minute rule was discussed during the development of both PMDG (744) and LDS1 (767), but I can't specifically recall if the 2 minute rule was applied to descents.Anyway, if we are talking about large descents in your scenario, then my comments become irrelevant. In this case, yes, I would say, that the aircraft should pitch down rather than add thrust with both types of aircraft whatever type of FLCH is fitted.Regards.Q>P.S. Note: I've seen the 2 minute target in both 767 and 744 maintenance manuals for a number of different airlines, but none specifically mention descents.

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Guest Darren Howie

HI QI'll have a chat to a mate of mine on the 400 and see what he says.I was under the assumption that similar to the 767 the 400's autothrust should hold the thrust at idel and pitch down for speed control on descent.If its a bit more complex than that as you say its excellent for pax comfort but boy it will make the aeroplane hard to fly in the real world down under!!Be interesting to hear what others have to say.Darren

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Related to FLCH, I find the during an IDLE descent, with each mouse-click to change the MCP speed, the AT mode momentarily jumps to THR and then right back to IDLE. This repeats with each mouse-click. Do others also experience this odd behavior or is it somehow related to my PC? It does not impact the aircraft behavior in any way, but is just odd watching the mode jump around like that.Rushad

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Guest D17S

I see it too. It

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Guest Darren Howie

HI SamWhat i have found at least onmy install is exactly what you have seen.However when i dial in a speed intervene which involves an increase of say 30-40kts over current IAS the thrust is actually coming up to help with the accel rather than by simply pitching down alone.SO my question still is 1)Do i need to reinstall2)Is it accurate like Q may have hinted at and thrust does help out with the 744 when intervene speed is used and a larger increase is selected when using FLCH.3)IS FLCH on the 744 an idle thrust function and speed should purely be controlled with pitch?CheersDarren

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>1)Do i need to reinstall>2)Is it accurate like Q may have hinted at and thrust does>help out with the 744 when intervene speed is used and a>larger increase is selected when using FLCH.>3)IS FLCH on the 744 an idle thrust function and speed should>purely be controlled with pitch?>>Cheers>>Darren1) I dont think so.2) Yes.3) No.All is explained in the fine manual... although the text does not go into specific details about parameters, the words "integrates" and


Cheers, Søren Dissing

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An older (Feb 11, 2000) copy of the QF AOM says:"A/T annunciates THR, followed by HOLD mode in descent. When selected altitude captured, A/T mode changes to SPD. A/T advances or retards thrust levers to maintain a vertical speed proportional to the altitude change requested."You said:"2)Is it accurate like Q may have hinted at and thrust does help out with the 744 when intervene speed is used and a larger increase is selected when using FLCH."I assume you mean larger increase in speed? If you mean altitude, I meant exactly the opposite. _Small_ altitude changes will result in a shallower profile for pax comfort, so I'm assuming that additional thrust will be required to maintain that shallow profile (especially if you dial in extra speed).You said:"3)IS FLCH on the 744 an idle thrust function and speed should purely be controlled with pitch?"It depends on how you interpret the above statement in the AOM (is it referring to both climb and descent?).I don't think that speed control will be a problem for emergency descents, as they usually involve large altitude decreases. The A/T&A/P will try to get you down within 2 minutes, so the throttles should come all the way back to idle, whatever speed you dial in.CHeers.Q>P.S. (Edit) Perhaps it would be best to clarify our statements by saying WHY we think something should be happening (preferably with manual references or real world aircraft experience or big sim experience). Having said that, it's always best to confirm what we think we saw in real life. For example, which airline regularly uses FLCH for 1000 or 2000' descents, then speed intervenes (not many, I'd imagine).

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Guest D17S

I believe it's normal to get thrust increases with FLCH speed changes under specific circumstances. Here are the dance steps as I see them: For a descent, FLCH Speed increase . . . 1) FLCH will pitch down to accelerate in response to the MCP knob command. Here, FLCH is the first mover. 2) This causes an increased ROD. THR sees this increased ROD (or decreased

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Guest Darren Howie

Thanks for all the cool info guys on the 400's FLCH finer points.I must say that for all its extra points for pax comfort i can now see why 400 drivers rely so heavily on the speedbrake for straight in ILS approaches for the final part of the decent.WIth sttep profiles being the order of the day around the world(IE 9000'at 30nm minimum) and no way to juggle aeroplane energy the boards are your only way out.Bit of a pity given how rough it is in any 74 with speedbrakes extended.Unlike the 400 Airbus offer you open decent a commanded idle thrust with pitch controlled by speed to allow you large ROD's as the aircraft accelerates to a newly selected increased speed.Even then on the 330 and 320 speeedbrake is needed to help out when at higher landing weights when flying straight in approaches at airports with steeper CTA steps.Thanks againDarren

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"Speed is still controlled by pitch and thrust is still controlling rate (time to target). There

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