At about FL260, the speed in the speed display should automatically change from IAS to MACH or reverse. I haven't seen that happen.Leo Bakker

Hi Leo,sorry for the dumb question, but are you in VNAV mode or else? In that case the speed window stays blank.Regards,Bjorn

HiThe changeover should occur when passing FL260. In VNAV pitch command mode you will not see any speed indication. The speed display on the MCP is only affected by this changeover in case of a LVL CHG or V/S climb or descent.I have just checked, and indeed the changeover does not take place, neither during climb or descent in either of the two above noted AFS pitch command modes (LVL CHG and V/S)Regards,Zoltan HegedusBudapest, Hungary

Hello,The change over does not occur at a fixed altitude. It occurs when actual mach equals the target mach (or actual ias / target ias in descent).It usually occurs around this alt, if speeds set accordingly.You might have a hard time changing over if you for instance lowered your climb ias and increased your climb target mach.cheersanthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

Is the MCP speed window supposed to change over automatically if you're in LVL CHG?Lee Hetherington (KBED)

Hi Anthony,To be honest, I don't quite understand what you mean. If I'm in LVL CHG, I can only set either IAS or MACH in the speed display, right? So what do you mean when you say "if you lowered your climb ias and increased your climb target mach"?However, I think your answer may be connected to the TGT SPD in the CLB and DES pages in the FMC, where there is a pair of MACH and IAS speeds. For this flight (as for most others?) the suggested pair is 315/0.755.So I tried again, this time climbing, above FL100, at exactly 315KTS, as suggested by the CLB page, but of course in LVL CHG, since using VNAV would blank the display. At around the famous FL260 change over point, the actual speed increased above Mach 0.755, however, there was no change over in the speed display. I continued until the speed was at around Mach 0,80 but at that point the climb was rather slow :-) Which is logical, since it was still trying to maintain 315 IAS.For the descent I tried the reverse. I used the change over button to get Mach, set it for 0,76 and LVL CHG down to earth. At about FL200, the speed pointer is at 360, almost in the red overspeed zone, and the aircraft is still maintaining Mach 0,76 in the descent.I'm positive that this isn't right. In fact, I think you'll agree :-)Leo BakkerP.S. I would like to repeat my earlier remark that despite my comment I really like this sim. There are so many little things that show the true ambition level of this sim. Taking off for this flight: THR HLD changing to ARM at 800 ft RA, check! Then at thrust reduction altitude from ARM to N1, check. Setting the A/P to command, which should engage LVL CHG automatically, check! Pull a fire handle while the master caution lights shows HYD, and HYD will extinguish, check! My compliments once again. I hope you don't mind my starting two new threads, though :-)

Leo,Start as many threads you like, that's OK ;-)I will check my changeover logic. Yes I was referring to the VNAV targets... But yeah.. what happens in vanilla LVL CHG ?I'll look into that !cheers,anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

Just my two cents on this matter. Isn't it so that the reason why the MCP logic automatically changes over in VNAV is because it takes information, and has transition speeds from the FMC? I mean like 300/.78. In any other pitch mode the plane can't really know when to change from IAS to MACH speed as it's not using the FMC data? Or is it supposed to use FMC data even in other pitch modes? I'm most certainly missing something here...lolRegards

FWIW, 767PIC's MCP speed window does not change over to Mach when in LVL CHG. I have no idea if that is correct or not.Lee Hetherington (KBED)

Don't know for sure, since I don't have any 767 manuals. However, on the 737 it works that way and I also know for a fact that is works that way on the 747-400, so I'd be surprised if it was any different on the 767. But you never know, it being Boeing's first glass cockpit.Leo Bakker

FL CH still simply serves to reach a certain altitude with a certain speed maintained, while speed control is achieved by pitch adjustments. The mode is not "intelligent" beyond this capability, you will have to manually change from SPD to MACH when reaching target cruising MACH number. The change over altitude varies according to speed/mach selected. The same applies to descend, you will have to change to SPD when you reach your target descend SPD, otherwise the aircraft would continue to accelerate while trying to maintain cruise MACH speed. But e.g. MACH .755 would be about 400 IAS at 5000 ft, thus far beyond the aircrafts overspeed limit.If you want more automatic, you will have to use VNAV and this is the mostly used climb mode in the real world. So, FL CH is not cautomatically changing from SPD to MACH.hope that helps

Okay guys (and girls - Kimberly - you here ?),We're getting confused now !This is what I'll do (in fact I did) :- VNAV transition as per current : when IAS reaches target mach, changeover, same logic in descent.- when non VNAV mode, crossover at FL26cheersanthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

Hi Andreas,I'm sorry, but what you're suggesting is simply not true. A direct quote from the official Boeing 737 manual:Chanegeover switch:- push: changes IAS/MACH display between IAS and MACH- automatic changeover occurs at approximately FL260My information on the 747-400 is somewhat more helpful in understanding what the thing does exactly at what moment. This is from the infamous Essco Northwest 744 manual:IAS/MACH window:- in climb changes from IAS to Mach at approximately .84 Mach- in descent changes from Mach to IAS at approximately 310 KIASNaturally these speeds don't apply to the 737, but the principle is the same: there IS an automatic changeover.Leo Bakker

Hi Anthony,Thanks for looking into this, I really appreciate it!Leo Bakker

"- automatic changeover occurs at approximately FL260"Would it do it even if you had no A/P modes engaged/armed?It would be interesting to know what initiates the changeover. MCP programming? FCC Left/Right programming? FMC programming? ADIRU programming? Of course, the display would have to reflect a failure of these in any simulation. To complicate matters, there may be a complex signal path involved. For example, on the 747-400, to change the airspeed bug on the PFD by turning the MCP knob, the signal has to go from the MCP to the FCC to the display computer to the PFD (via a number of databusses/relays)Cheers.Ian.