The overspeed and underspeed symbols in the speed display are one of those nice, innovative features of this sim. However, they're part of the command speed limiting system, which means that by adjusting either pitch or thrust the aircraft will maintain a speed that is just above the minimum speed for the current flap setting or just below the maximum speed for Vmo or flap or gear limit, even though the speed set in the display may be different. The flashing symbols indicate that this speed limiting process is taking place. However, this part is not functioning. The aircraft will quite happily fly itself into the red bands, which it shouldn't.Leo Bakker

I seem to get in the habit of replying to myself :-)However, for another thread I dug up the following slightly more detailed information about the minimum speed reversion, so for clarity I thought I'd include it here as well.In the Boeing manual several reversion modes are mentioned, one of them is minimum speed. In my Lufthansa manual more or less the same description is given, but here it's called maximum angle of attack reversion. Maybe it's just a matter of terminology?In the Lufthansa manual the description is quite detailed. Some highlights:- 1.3 Stall speed is referred to as minimum or alpha floor speed. It will be the same as Vref at forward CG, as the CG moves aft the alpha floor speeds will be lower than Vref- A/T will display the underspeed symbol as it's getting close to the minimum speed, in proportion to the deceleration. It will control speed to maintain minimum speed and will display the underspeed symbol until the actual speed is 5 kts over the minimum speed. With both A/T and AFDS capable of reversion, A/T will control first.- AFDS reversion mode works in V/S, VNAV SPD or LVL CHG, but is inhibited when in ALT acq, capture or hold or after G/S capture. Detection occurs at minimum speed if A/T switch is off, or 5 kts below when A/T in arm to reduce conflict with the A/T. When AFDS reversion takes over, it reverts to LVL CHG, the underspeed symbol will become visible at this time and the speed display will show CAS, or last valid FMC target airspeed when coming out of VNAV SPD. It will command minimum speed + 5 kts, the alpha flag will remain in view, until the actual airspeed gets 15 kts above minimum speed. For that to happen you have to set the MCP speed command to a higher speed, of course.The Lufthansa manual is for the 3/4/5, but I think it should work the same way in the NG.Leo Bakker

Leo,Just answering so that you do not feel alone :-)Try this to check stall protection. Level off at some altitude (value is immaterial). Command some silly low speed (AT armed, AP engaged). Watch the plane increasing pitch and going towards stall...Have faith. AFDS will revert to LVLCHG near stall and command 1.3Vs + 5. Note : Actually AFDS works with angle of attack rather than raw speed but system will is tuned to kick in at 1.3Vs. Cool huh ?Reset commanded IAS and resume normal flight.Best Regards,Vangelis========================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com==========================================

Mmm, fascinating! It does work the way you describe, although the speed will briefly get into the red band and I get a stall warning before the system gets itself out of this nasty situation. While I'm writing this, my airplane is happily cruising along at FL100 at 151 kts, exactly at the top of the red band, with the A flashing next to the 100 kts I set in the speed display. Great!However, previously I really DID manage to get myself into a complete stall, but since I didn't document this "experiment" too well, I can't seem to reproduce it. If I'm ever able to reproduce it again I will let you know. Maybe it was pilot error after all :-)Anyway, thanks for the information!As far as the overspeed protection goes, however, apparently I have to plead insanity :-) I'm still at FL100, now doing 240 kts with flaps 15, well into the red band. I'll give some direct quotes from my Boeing AOM, in the automatic flight section under the heading of Command Speed Limiting:The AFS provides speed, pitch and thrust commands to avoid exceeding the following limit speeds:- Vmo/Mmo- Wing flap placards- Landing gear placardSpeeds greater than Vmo/Mmo cannot be selected from the MCP. If a speed greater than a placard speed is selected the AFS allows acceleration to slightly short of the limit, then commands the limit speed. The overspeed limiting symbol appears when the commanded speed cannot be reached.BTW, by Boeing manual I mean the AOM that is issued by Boeing, meaning it's not a company specific manual.Kind regards and thanks for the company :-)Leo Bakker

Probably a little off topic, but one for the Avionics guys....Had a problem on a 747-400 recently where the min manoeuvre margin (yellow band) was sitting too high on the airspeed tape (even higher than the selected flap marker), causing AIRSPEED LOW Cautions on approach. We checked the FMC Perf Factors, changed the left AOA sensor, then the right, interchanged lots of components, ran lots of Central Maintenance Computer Tests... all showing OK, but the problem kept coming back. Eventually had to change both Stall Warning Computers to fix the problem.Having 2 identical computers fail at once is mystifying :-abduct Cheers.Ian.

>Having 2 identical computers fail at once is mystifying :-abductProbably a bug in the system software initiated by the same combination of inputs on both comps. ;-)Regards,

"Probably a bug in the system software initiated by the same combination of inputs on both comps."Or the same voltage spike :-) Maybe even a "bolt from the blue"? (I'd better check the fuselage skin for black marks next time the aircraft comes my way ;-)Cheers.Ian.P.S. The Stall Warning Computers are probably undeserving of their name "computer". They are very basic... I doubt there would be any reprogammable stuff in there.

wow very very very interesting!

To lonely Leo :Dear Leo,In the upcoming patch you will find an overspeed protection system I implemented (clean, flaps, gear etc). As per AOM the AT/AP system may allow acceleration past overspeed limits by a small margin before taking action. However, target IAS or Mach exceeding the limit will be autoamtically reset to the limiting value. The system is therefore somewhat intricate and will basically :(a) try to reduce speed by throttle control (:( if not or moderately succesful will revert to LVLCHG (idle power) with a timed delay which depends on conditions © Stall protection will override overspeed protection ("coffin corner"). Note : I deal with the automatic control system not the user interface which is the MCP.[(d) I wait to see the first complaint of the type I was descending in VS with AT off and plane started all by itself levelling off then climbing then descending at its own rate you-good-for-nothing-you blah blah blah. I'll forward all email to you, Ian and Lee :(](e) Lets see how much more technology we can pack in a $40 bundle ! Have some more ideas...Best Regards,VangelisPrivate joke : Do you have to read posts so insanely fast :-) Cant even edit.

Well, thank you very much! I can't wait for the e-mails to come flooding in :-)BTW, I personally don't think you have to get the complete aircraft in a $40 bundle. But I wouldn't mind :-) No seriously, as you have noticed I will mention differences that I see between this sim and my manuals, down to the last detail. It's up to you to decide what to do with it. But I will be honest about this: I really do hope this will, in time, turn out to be the 737 version of PIC767 or even better. From what I've seen, I'm confident that you guys could do it. And if it means I have to pay for two upgrades to get there, no problem for me. I do realize the immense complexity behind all this and if it takes some time and money to get it all right, that's okay. (At least with me...)Leo BakkerPS. How about making it the PS1 of MSFS?

>>Leo Bakker>>PS. How about making it the PS1 of MSFS?Well,knowing those guys it is posible.They can make miracles:-)Keep up the Good Work PMDG and this is going to be THE BENCHMARK!Baper