Hello,I've just finished the advanced tutorial for the MD11 and am really amazed with the quality of this add-on aircraft. It's really a wonderful feeling to have studied the plane for about 50 hours and still knowing that you have just learnt a tiny bit of all there is to know about it.Anyway, the descent on this flight went without any problems but I have noticed on other flights that I usually get the "ADD DRAG" message although I've entered the winds correctly in the FMC prior to departure (only on the INIT page - not manually for each waypoint in the FLT PLN). Getting the "ADD DRAG" message I deploy the spoilers but what I see then is that the ATS increases the thrust up to around 60-65% N1 and constantly stays about 100 feet above the profile. In the advanced tutorial I saw the following sentence: "Now if for any reason ATC asks you to expedite a descent, in this situation you would not pull the speedbrake lever but instead select an idle clamp descent via the FCP." (p. 33). I am well aware that no profile calculation will be perfect and depending on the winds I will get the "ADD DRAG" message now and then. What surprises me is that the AFS/ATS seems to be working against me when I try to resolve the situation by deploying the spoilers.So my questions are:1. How do you select an idle clamp descent via the FCP? Or is this just another way of saying "FL CH" (pull the ALT knob)?2. Have anyone else experienced this problem; that the ATS is counteracting your deployment of spoilers with increasing thrust when above the profile? It also seems like the thrust generally is set to around 45% N1. Wouldn't it be more economical to idle the thrust completely (25% N1)? I could try to post some screenshots if it is necessary in order to tell what is going on. Regards,Per IsacsonP.S. The FMS is setup in policy descent speed 290 and I have no anti-ice deployed.

1. Yes just pull the alt knob2. The only time the ATS increases thrust for me is if I leave the speedbrakes on too long and are going off profile or speed in the opposite direction. As for idle N1 speed that depeds on airflow, on the ground the FADECs can hold the engines at 25% N1 but in the air with a IAS of 150-330 it all depends on what speed you're doing. Saying that the throttles are still in idle clamp and being fuelled for a idle but the airspeed pushes the N1 fan blades faster.

1. Yes just pull the alt knob2. The only time the ATS increases thrust for me is if I leave the speedbrakes on too long and are going off profile or speed in the opposite direction. As for idle N1 speed that depeds on airflow, on the ground the FADECs can hold the engines at 25% N1 but in the air with a IAS of 150-330 it all depends on what speed you're doing. Saying that the throttles are still in idle clamp and being fuelled for a idle but the airspeed pushes the N1 fan blades faster.

I really dont think No 2 is correct?? the minimum Idle thrust that the FADECS command depends on the aircraft being on the ground or in the air, A/I on or off etc. Airflow over the N1 fan does not make that big a difference.

This is one that might not be intuitively obvious. The fans are large and easy to rotate (watch them spin in a mild breeze with engines off), but is that is enough to spin up the N1 number? I wouldn't bet either way on this one. I would bet that this effect, if it happens, is included in the MD11 simulation and I agree with Jay that N1 is not an indication of thrust.

Thanks for the replies! I just tried disconnecting the ATS and for whatever reason it seems, like you say, that the engines keep an N1 of around 44% at 20,000 ft with the throttles idle. I also changed some altitude constraints on my way down to get a couple of thousands of feet above the profile. In this case it looks like the ATS is more cooperative and really keeps the throttles idle. In the situation I referred to above I was more like 100 feet high when N1 went up to over 65% while "ADD DRAG" was still displayed. I'll investigate more on my next flight.

I really dont think No 2 is correct?? the minimum Idle thrust that the FADECS command depends on the aircraft being on the ground or in the air, A/I on or off etc. Airflow over the N1 fan does not make that big a difference.

As mentioned the fan is easy to spin and not liked directly to compressor, having a few hundred knots of air going through them would have to spin them up a bit (why you can relight them mid flight without bleed air).In the PMDG MD11 travel upto around 310 knots throw the throttles into idle and watch, it falls to around 50% N1 (throttle indicator on the EAD in the same location as on ground idle) then as the aircraft slows the N1 speed slows until the low speed protection cuts in. Why would the FADECs command a higher idle speed the faster you go?

Why would the FADECs command a higher idle speed the faster you go?Hi Jay, I probably shouldn't have posted in such a rush, I didn't mean the FADECS command a higher N1 the faster you fly. I was trying to say that the FADECS command a minimum IDLE 'Thrust' Depending on the flight condition, eg 'Flight Idle' 'Ground Idle' and increased Thrust depending on the pilot selecting Anti Ice for engine bleed air. Regarding the windmilling effect and N1 rotation speed you can achieve for a inflight engine restart - I never knew you could get it as high as 50-65% N1 so I have learnt something new today :) Anyway it's Bank holiday weekend here in the UK and the other half has banned me from the PC so have to run again, happy holiday's to all the other UK simmers.Cheers