Idle -> ARM problem

[namida 0]

Hello guys. I sometimes struggling to reduce speed while descend because idle thrust stays more than idle.Usually when aircraft enters DES phase or changed from DES SPD, A/T mode goes IDLE, then finally ARM. But occasionally N1 stays 41~42 than 33~34..I don't know exact condition for A/T choose which thrust.. Additionally, when I press F1 key to make complete idle, it goes down to 33% N1 as I expected,(but sometimes A/T holds 40's again.. PFD still shows ARM, no change) I'm experiencing NGX flies faster than target speed.Am I missing something..? I don't use CRZ SPD but it happens both with winds or clear skies. Any advice appreciated!

[davierosoft 13]

Idle control is controlled by EEC, it decides to change it by increasing, decreasing N2 (N1 follows).Some inputs that changes idle engine speed are:Flap positionanti iceflight/groundAltitude (15500ft)So, the true idle is only on ground at the engine start up.

[namida 0]

Idle control is controlled by EEC, it decides to change it by increasing, decreasing N2 (N1 follows).Some inputs that changes idle engine speed are:Flap positionanti iceflight/groundAltitude (15500ft)So, the true idle is only on ground at the engine start up.

Thank you Andrea, the info you appointed - especially Altitude - helped me.But the key point of my post is it stays higher than it commands. If ECC controls N1 (you commented it controls N2 but I'm just writing this for convenient) for 42, it should remains even I press F1.It drops for a second and go back to 42%. But sometimes it drops to 32 from 42 when I press F1. This makes me confusing..If ECC commanded it stays to 42, it shouldn't drop.

[Cristi_Neagu 134]

That appears to be an issue with FSUIPC.

[namida 0]

Thank you Cristi for another perspective. But it's does not seems a hardware issue.. Maybe you're talking another thing I do not know?I use F1 key because throttle override option has turned off, and same result when I move throttle to idle with option turned on.

[emvaos 13]

Something is miscalibrated in your throttle axis / throttle setup and overrides the EEC command. Re-calibrate and reset axis from FSUIPC for starters.

[namida 0]

Thanks for reading this post, emvaos.But as I wrote in #5, my throttle stays at 30's N1.. (blue arc)I explained it is NOT a hardware issue. I'll rewrite this a tidy version. When I descend with Idle - ARM,- A/T goes 32% N1 and it's all right. (either manual override on or off - I always set throttle to bottom when cruising) - A/T goes 42% N1 and I press F1 or move throttle to idle(retard, i mean) - with override is on, it shows white arc drops to 32% but bo back to 42% N1. (seems normal for now)no problem in this case. No overspeed beyond FMC SPD limit. - A/T goes 42% N1 and I press F1 or move throttle to idle - with override is on, it shows white arc drops to 32% and N1 actually stays 32%.in this case, even Andrea adviced it differs with altitude, happens below 12,000ft and NGX descends faster than FMC SPD. (definetly need spoilers) So, A/T stays 42% N1 when it should stay at 32% from time to time..

[Paul Deemer 13]

At the top of descent pull the throttles back to the idle position and leave them there while descending. Use the speed brakes as needed to keep your speed down. Might also help to use a reasonable Cost Index number such as 40. If you use 80 like the bigger jets it will descend like a rocket at 330 knots. If you use a Cost Index of 40 it will descend at 283 knots. Idle speed on the ground is around 21% but when descending it is around 40% this is normal.

[FreaXter 0]

i have the same problem here. N1 stays at 41-44% during decent. and then fmx says "DRAG REQUIRDE". if it would reduce to 31% or someting like that, no drag would be required. i think it is not common to use the speed brakes during 60-70% of the whole decent path. pressing F1 pulls the throttles back to 31%, but......magic......they come forward again just a few seconds later. the only thing so solve this is turning all autoflight systems off and on again or to switch to level change... it is a bug, i'm really sure...

[davierosoft 13]

i have the same problem here. N1 stays at 41-44% during decent. and then fmx says "DRAG REQUIRDE". if it would reduce to 31% or someting like that, no drag would be required. i think it is not common to use the speed brakes during 60-70% of the whole decent path. pressing F1 pulls the throttles back to 31%, but......magic......they come forward again just a few seconds later. the only thing so solve this is turning all autoflight systems off and on again or to switch to level change... it is a bug, i'm really sure...

It is a bug if throttles come back to 31%, not the 40%,To help the FMC to calculate correct descend with no drag required compile correctly the des forecast so the plane will correct the TD, also use correct cost index.Maybe F1 key command the throttle on low idle, keep pushed it and see if it remains at 31%, for me is not a bug as the real one doesn't have a F1 key. If you find it uncomfortable, ok, think at it as a bug, but I think it will not "solved"

[MrPlaneDriver 41]

Well, here's my point of view on that. What I noticed is that if you pull the throttles all the way back, until the point where you can pull no further, the N1 stays at 31%. What I see the EEC doing is to push the thrust levers a little bit forward, enough to keep N1 stable at 40%. So when the EEC sets the thrust to 40% N1, it is actually moving the throttles forward, I mean... They are not in the full idle position. If you look at them and press F1, you'll see them moving back and then forward again to return to flight idle. So if you press and hold F1, you can force the engines to maintain 31% N1, because that way you're forcing the levers to the "full idle" position. Even though the FMA says the thrust setting is in ARM mode and you should presumably be able to set whatever thrust setting you want, the EEC is taking a little action on not letting you enter full idle to prevent a stall. I notice the N1 increasing to 41% at the time I lower the flaps to 1 or lower the landing gear. That really does not look like a bug to me. Another thing is that I hardly use spoilers during descent. I usually fly with a CI of 25, 30 for longer flights, which gives me a nice 267-271 knots descent speed, and I also enter winds information in the FORECAST page, as well as ISA deviation and QNH at destination at about 80nm from ToD. This plane needs some planning ahead for descent because it really struggles to lose speed, so entering some speed contraints like 180 knots at about 10, 15 nm from intercepting the final approach course and 160 knots on the interception point or at 10nm from the runway also helps a lot.

[davierosoft 13]

Ok, I will try, and if it is, so it is a bug.

[namida 0]

At the top of descent pull the throttles back to the idle position and leave them there while descending. Use the speed brakes as needed to keep your speed down. Might also help to use a reasonable Cost Index number such as 40. If you use 80 like the bigger jets it will descend like a rocket at 330 knots. If you use a Cost Index of 40 it will descend at 283 knots. Idle speed on the ground is around 21% but when descending it is around 40% this is normal.

Thank you for advice Paul, but I already doing that. As soon as I push TO/GA, I move throttle back and always use CI 40. And I know flight idle and approach idle is more than 40% and it decreases as you descend.Sometimes it stays 42% N1 as idle thrust is 42%. THIS IS OKAY. THE PROBLEM IS even flight idle is 30s, SOMETIMES(not always) retard - arm mode make it 40s..AND at that point, it is a bug itself, and WE CAN CONFIRM it's not at full idle status pressing F1 to move to full *FLIGHT* idle. I've been writing same things again and again..I appreciate for replies but please read slowly because my English is bad.. even

[davierosoft 13]

Mhhh... found what you mean, in effect the throttles are not in idle when on approach idle, also if AT is disconnected, by retarding joystick lever or pushing F1 will slow down the engine below approach idle, then the levers will automatically moves (when they cannot do) to restore power.The wrong thing is not the approach idle or the value, but the levers movement.

[JC75 22]

I understand you Peter!Peter isn't talking about the different values that "idle" may be at various stages of flight set by the eec. He is more than aware that in the real plane even with the levers fully back the value for idle will be different at different times.What Peter is saying is that sometimes when the eec is commanding a change in that idle value it isn't actually sometimes selecting the lowest idle value that it should be at that stage. And intervention with manually resetting the throttles to idle will then get the correct idle value. So you are in descent, the eec is commanding idle, you have your throttles all the way back, and you get an eec commanded value of 42, you then push and pull your throttles back, in in peters case select f1 and see the value reduce to 36 say but the eec doesn't then push it back to 42 it sits happy at 36 which shows it should have been 36 not 42. Other times it will o back up to 42 which shows that is where it should be.Basically it seems sometimes once an idle value is set by the eec, even though it should maybe be now reducing that value further it doesn't, unless you physically intervene to check it's got the right one.This issue could be why some users get reverse thrust issues also on landing, as again the approach idle hasn't actually been set to the lowest approach idle it should be at.Peter a simple test to try is actually trying it without any throttles plugged in, I know you say you set setting in fmc for them not to overide, but see if same issue occurs when not plugged in at all, just using keys and mouse on vc throttles.