By a/t off I meant that the speed is not controlled by the autothrust system.Tero

As always the FMA will tell you exactly what the systems are doing.There are two scenarios here and several permutations.1. First is A/T is in ARM, this will provide speed protection in the normal flight envelope but don't know what it does when you are within say 27' RA of ground in landing config.2. Is same but with A/T in MCP SPEED and again this business of it closing the thrust leavers when within a ceratin height of tehground and so in is beyond my knowledge or experience.There are several pother factors here as well.. are both or a single NAV tuned to a valid ILS freq, are you on GS etc etc.Ian R has very kindly sent me an email for which I am most grateful and I will take this issue up with our enginners. Here is an excerpet from Ians email:That's what the NG will do if you do leave the A/T on. When I first read this in the Maintenance Manual, I was very surprised to hear that a Boeing aircraft would do this.... If you didn't know this and were asked, say, to do a very low flyby demo at an airfield (with ILS) and you happened to have the A/T engaged, you could end up in a lot of bother (I'm thinking Airbus and trees here ;-)).Ask your engineers to get you a printout of the Boeing Maintenance Manual "D&O" Chapter 22-31-00 A/T SYSTEM-OPERATION-APPROACH ;-) ('round about page 81)Straight from the horses mouth Gents :D)Once again, isn't it wonderful tohave so many ppl interested in a great hobby!ATB,

Hi Brad,Copy those :) Ian R is quite a machine with those things... have gotten to know his "flare" for those kinds of things lately very well ;).Also, it IS great to have such a hobby. Flying in the internet with all the goodies is just amazingly fun and educative. And challenging too !Tero

GuysNo one seems to have covered the real reason for taking the A/THR out in the first place so I will, if nothing else it might help people understand the logic behind it.The B737 along with most other large jets have engines mounted below the wings, this means the engines are mounted below the centre of gravity. So consider this, if you push the power levers forward you get a push from the engines below the CofG. This push causes the nose to raise quite significantly. The oppisite is true when reducing power (ie the nose drops). This is known as the 'pitch power couple'. When manually flying the aircraft once you are relatively proficient you can take this into account and can predict the pitch changes when you move the power levers by trimming as the pitch moment occurs. So if you are moving the power levers yourself you can predict the pitch change magnitude and timing fairly well.Now consider that you are hand flying an approach and leave the A/THR in speed mode. Each time you make a pitch input the A/THR will compensate for the loss of gain in speed by moving the power levers. When the power levers move you get a pitch change and so you need to correct that pitch change. Guess what happens next, yes the A/THR senses a change in speed due to your pitch change and so the circle continues. This makes the approach very untidy and can be very unpleasant and possible dangerous. As someone has said before, if you are hand flying then hand fly (no A/THR). We deselect Speed mode and keep A/THR in the ARM mode to provide automatic TOGA power in case of a go around. If you disengage the A/THR completely then you loose that facility and would have to manually set the thrust on a go around. By having the A/THR do it you reduce your work load.Having said all of this, I don't think the PMDG aircraft simulates the pitch/power couple but I just wanted to outline the reasoning behind it all.Hope that helpsKris

Kris,I had a bit of a quarrel with someone regarding pitch/power couple during the beta testing of our version 3 757 FDE. The person insisted that our beta didn't have enough of it present, while four (4) 757 pilots told otherwise, and claimed that the effect is very very subtle, and was spot on in V3.I know it's not the 737NG we're talking about, but one would expect the magnitude of that effect to be alike in those two aircraft. My question is thus: is pitch/power couple very evident in the 737 series ? If it is, then why it isn't in the 757 (and even less in the 767) ?One explanation I have learned long ago for the reason for NOT using A/T when hand flying is simply this: A/T system is designed to work in co-operation with AFDS system, enabling steady, pre-calculated adjusting of power in autopilot coupled operations. If it is used when hand-flying, it tends to oscillate and chase settings (and this is surely partly because of your explanation above!), and the flying becomes rough and unsteady. Also there might be a mental mixup of the question "who is flying this aircraft, who controls what ?" when automatics and manual operations are mixed. Could be confusing in surprising situations...cheers,Tero

TeroThe magnitude of the pitch power couple I suppose is relative to the person experiencing it. If you are used to it then you don't notice it. so coming from a turboprop background it was quite pronounced to me during my sim training and on the aircraft. As you get used to it then you tend not to notice it and compensate automatically. The B737 will pitch to over 20 degrees from 3 degrees pitch when going around if you don't counter the pitch caused by the engines. That is on our 22K CFM56-5B2 engines on the 300 series. There are many reasons why the 757/767 differ, weight, pitching moment, size of stabiliser, thrust to weight ratio, distance of thrust vector from CofG etc etc. All aircraft differ in some ways. All I know is that when I first started on the B737-300 it was difficult to keep up with the pitch/power but you learn quick and now it is no big deal. I agree there could be some confusion over who is flying the aircraft but that is secondary as to the viscious circle that you find yourself in while fighting the A/THR inputs.RegardsKris

Hi Kris,Interesting information! Thanks.cheersTero