Randy,>> Tons of work in this area Mike but as you know nothing is like the real thing in this regardOk, sounds good again. Although I sometimes think, that kind of things are more important than the latest and greatest FMC or system detail. But generally you are right of course, we shall stay on the carpet regarding realism in FS :)Mike

Ah heated debate!Well it seems the 737NG isn't very good at keeping its speed spot on. It will sometimes happily fly around with the speed 8-10 knots under or over its commanded speed and do nothing (or almost nothing) about it. The autopilot logic is a bit crude, it's not as smooth as all the other Boeings. Having flown the 757, which is very very smooth when it comes to level changes, it's quite interesting to see the 737 autopilot behave. Boeing even tells you to use vertical/speed to climb or descend small altitude changes because LVL CHG is way too aggressive. Iz(now real 737NG dude)

Perhaps we need to install a co-pilot who makes smart arse remarks about "passengers turning green", and "Got a hot date tonight?" to deal with the fact that there are no fare paying passengers in the back who are going to file complaints when the plane lands ;-) Technical specs and smoothness rarely mix well. Remember your first flights with your eyes glued to the stupid needle bobbing up and down by 100 feet? It didn't settle down until you stopped looking at it :-lol Ray

>> It will sometimes happily fly around with the speed 8-10 knots under or over its commanded speed and do nothing (or almost nothing) about it. Oh, now I know why the Microsoft default AP does that all the time. They must have asked an NG pilot :DMike

Controversial discussions about the NG are always interesting, so I asked the NG driver I know about a comment. Here goes :"That kind of described speed inaccuracy sounds weird to me. At least our NGs don't behave like this. You can imagine, speed accuracy esp. below 10000 is vital, so as said before, this would have raised a lot of eyebrows.Yes, LVL CHG tends to be aggressive, we had that subject already. So we generally avoid it below 10000. Not using LVL CHG for small altitude changes is obvious, but not an NG speciality. You won't do that in a 744 as well :)"Mike

Hmm, has this guy even flown the 744? Actually V/S is almost never used on all other Boeings except the 737.The 744 APFD is exactly the same as the 757/767 and FL CH is always used, except by older pilots who transition from the older 747s or 737 and are afraid of pressing FL CH. In the 737 (all generations) the LVL CHG function will go to max CLB N1 setting for climb and IDLE for a descent and pitch up/down accordingly. The more advanced aircraft (ie. 747/757/767/777) will simply add or reduce a reasonable amount of thrust and very smoothly intiate the climb/descent and level off. So you can use FL CH even if you want to climb 300 ft. It's super smooth. And a lot more economic and simpler than playing with V/S.Even though V/S is automatically armed on the 737, on the other aircraft it is not (for the simple reason that you should use FL CH). So you would need to reset your MCP altitude, then select V/S and then scroll the thumbwheel till it's exactly where it should be. Just a press of the FL CH is all you have to do.The 737's autopilot is not very passenger friendly, when climbing, descending or rolling into a turn. The 747/757/767/777 autopilot is. In fact, in these aircraft, a normal passenger will not even notice the majority of intermediate climbs, descents and turns (except when looking out the window).This said, the 737 is the most speed-unstable machine in the current Boeing line-up. It requires more inputs in the pitch and thrust channel when compared to the other Boeings. This also explains when the speed will go up or under the commanded airspeed more.Why do you think that standard Boeing FMC speed value below 10,000 ft in the descent is 240 knots and not 250? There is a speed variance tolerance for 10 knots when it comes to Rules of the Air, so ATC will not chew your head off when you happen to fly 257 knots under 10,000 ft. Nonetheless, Boeing builds in an additional 10 knots margin (this goes for all Boeing models, by the way). Another thing, speed can vary through every phase of flight on any aircraft. This is tolerated within about a 10 knot margin because it prevents too active movement of the autothrottles chasing the airspeed all the time. Just like driving on cruise control, it uses less fuel to use minor throttle changes instead of making large changes to keep the airspeed on the bug even tighter (just as it costs more fuel when you drive off cruise control, you make larger corrections with your foot). So this kind of speed variance is allowed and normal.It becomes important if you're in turbulence or gusty winds, because that will cause large speed variations. Constant movement of the throttles will also cause extra wear and tear on the engines.All thrust settings are done with reference to a target thrust setting. For example, during cruise the FMC might calculate 80% N1 as the target setting to maintain M.800. Now it will primarily set thrust there and deviate from that number only very slightly. It is not a system that works purely on a feedback basis where it checks the airspeed and sets thrust accordingly to get back to the target airspeed.Hope this helps, I don't see how your pilot friend could see this any differently.Iz

Thanks Iz, that's a very interesting reading. Sounds reasonable and will certainly contribute to my PMDG 737 flying "style" ;). Although everytime I think I have a certain picture of the NG, I read something different. The controversial infos just reminds me of many threads at the real world pilots forum at pprune.org.If I follow some tech log threads there about the 737NG, I am sometimes scratching my head if the involved pilots really talk about the same aircraft. And just BTW, the same stands for e.g. "to LVL CHG or not to LVL CHG in a 744". I let my pilots friend know what you said, but he is on tour now for a few days.Mike