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Egbert Drenth

Fadec During Descend?

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Hi,Recently I bought the Feelthere Legacy which is equiped with FADEC.I have a question about FADEC (in general), specifically during descend below FL100.I descended from FL90 to 4000 with a V/S of 1500ft/min.The FADEC controlled the engine idle thrust, setting it at about 50% N1.This caused the aircraft gradually to speed up again, from 220kts to 250+ kts.Is this normal? I mean normally idle thrust is between 20-25%, but appargantly not for FADEC controlled aircraft.How is speed controlled with such a high idle thrust? Speed brakes, flaps?Most likely I did something wrong (FMC setting, other?) or is this the way it works?Egbert

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Hi Egbert,Those Idle thrust settings sound wrong so nothing to do with FADEC. The aircraft will normally give you approach Idle which is slightly higher then ground Idle and if modeled correctly Engine anti ice will give you a higher idle thrust setting.It all depends on ambient conditions around you and in normal ops speed brakes are needed especially if you are not descending on the correct computed vertical path. But anyway like I said that N1 seems to high.Edit - Just noticed you where performing the des in V/S does the aircraft not have a VNAV or FLCH equivalent? In the 744 if I leave the aircraft in VNAV the thrust mode will switch to IDLE then HOLD allowing me to manually select an Idle thrust setting even with the A/T still connected speed protection is incorporated in case I don't move the throttles from idle after level off.Rob

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Edit - Just noticed you where performing the des in V/S does the aircraft not have a VNAV or FLCH equivalent? In the 744 if I leave the aircraft in VNAV the thrust mode will switch to IDLE then HOLD allowing me to manually select an Idle thrust setting even with the A/T still connected speed protection is incorporated in case I don't move the throttles from idle after level off.
Hi Rob,Yes FLCH is available, but that is not something one would use during (final) approach phase, at least I don't.Don't know about the hold function in combi with the speed protection in FLCH. I'll check.Egbert

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HiNothing wrong with using FLCH before G/S intercept as you should have full speed protection. I only fly online so prefer to use VNAV due to having the ability to punch in the ATC speed and altitude constraints in the FMC if they are not the same as the loaded STAR. If I was descending at 1500 on V/S it is unlikely the aircraft would be descending fast enough for Idle thrust, especialy if at MLW. But that's on the 747 so not sure how the Feelthere bird would behave.FLCH main purpose is the give you the best rate of climb/descent based on 'your' commanded speed.Rob

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