Climb speed issue.

[ViperXBR 32]

Before placing a support ticket, thought I'd post this issue here to see if anyone else experiences this or may know what the issue may be.The problem I'm having is during my climb, as I'm passing through FL300, my Indicated airspeed does not adjust automatically as the "barber pole" comes down the speed ticker tape and the Mach number increases. An example of this would be if my Climb speed is set to 315/0.793 and CRZ altitude of FL350, it will keep the speed bug indicator on my indicated speed of 315 all the way up to FL350. At that point though, 315 knots indicated is well within the Overspeed range (Barber pole). The system does adjust this speed to the Mach value when achieving these higher altitudes until it reaches Cruise altitude. Then it falls into the proper Mach value.Anyone know what is going here? Read threw the whole tutorial and i can't find anything as to why this may happen. These speeds are set by the FMC in ECONO mode. No manual intervention. Noticed this after applying the SP1 (did a complete removal and re-install of the NGX and SP1).Thanks,Todd.

[emvaos 13]

What are you doing ?Because to begin with in VNAV without SPD INTV this is impossible to happen. Just did it in fact. Changeover altitude on a standard day is FL290 or so (for thi9s speed schedule).So, I repeat, what are you doing ?

[scandinavian13 5,192]

The only thing I can think of is that there's a weight discrepancy. The plane does really weird things if it's expecting kilos and you give it pounds. It thinks it's insanely heavy and does some odd things.

[emvaos 13]

The only thing I can think of is that there's a weight discrepancy. The plane does really weird things if it's expecting kilos and you give it pounds. It thinks it's insanely heavy and does some odd things.

This will affect your buffet speeds and result in gross mis calculation of performance. Garbage in -> garbage out.

[HiFly 16]

The tradeoff between airspeed (make sure you are using IAS in the FSX, BTW) and Machspeed is dependent on OAT or SAT. On a colder than standard day (Standard Temp lapse is approx 2C/1000 ft) the aircraft will reach a higher mach value at a lower true airspeed. Conversely, in a higher than standard temperature day, the aircraft will require a higher true airspeed before that mach value is reached. The reason is that the speed of sound is faster in warm air than in cold air. When climbing at a fixed "Indicated" airspeed the true airspeed is increasing as you climb. The point at which the aircraft changes over to Mach (as programmed in your FMC climb page) will require higher altitude on warm days, lower altitude on colder days. It is very possible that using a high indicated airspeed (by choosing a high CI in the FMC) could result in the aircraft reaching Vmo (maximum safe operating speed indicated by the RED bars on the PFD) before reaching the Mach change-over point if OAT is extremely warm.Now with all of that, two things to check. First is when you are at FL300 as you indicated, what is the Outside Air Temp? Standard Lapse rate on a standard temp day (15C at SL) would mean that the OAT would be 15C-2CX30=-45C. Now if the surface temp were higher or the lapse rate varied then the OAT could be different than -45C at this altitude but usually in the same range +/-15C at the extreme. If you suspect upper level temps to be high on a given flight you may want to climbout at a lower mach speed by setting it lower in the FMC climb page. Some companies used to require 280K/M.76 under most conditions. Doubtful you would have experienced Vmo before the changeover in that case. In the B757 that I used to fly we usually climbed at 300K/M80 back in the days when fuel was cheap. Now I think they are using 300/M78 and cruising at about M80, but I digress. Anyway hope that sheds some light. Oh, and BTW, some wx programs have been known to wrongly display upper level temps and this can really muck things up. Better check that too.

[ViperXBR 32]

Thanks for the responses.Like I said in my original post, I'm following the tutorial that came with the NGX. The only difference is different departure/arrival destinations, route, and slightly higher altitude. Using pretty much default payload. Fuel adjusted the same way PMDG mentioned in the guide via the FMC.Using ASE for Wx. I've been doing nothing different since I installed this aircraft back in Aug. The only item that has changed since this started happening has been the applied SP1. Maybe something from the service pack has changed the way the FMC should be programed? Therefore, the tutorial is no longer correct? That's only thing I could see or else it's a bug.

[emvaos 13]

The word is bug is used to often. VNAV will change from IAS to Mach long before the barber pole. In fact it is impossible to exceed not only the barber pole but Vmo - 5 / Mmo - 0.01 (CLB/CRZ) and Vmo - 10 / Mmo - 0.02 in DES(cend).What is your pitch mode? What is your thrust mode? Read the FMA (this is how glass jets are flown). Help me to help you.

[Turnex 0]

I have the same problem and would like to know if the original poster found a solution? For me it seems that the speed bug never makes change over from IAS (showing 315 kts) to mach speed when in VNAV mode, eventually resulting in an overspeed condition if left in VNAV. The only work-around I've found so far is to change vertical mode to LVL CH, manually press the change over button, and leave it there until CRZ altitude is reached where I can switch back to VNAV. If I switch back to VNAV mode after doing this, the speed bug reverts to 315 IAS. The problem only started after I made a fresh install with SP1. I've tried a handful of different combinations, both starting cold & dark at parking and with engines running on the runway, and with two different routes, each one manually typed into the FMC. In each case all the relevant pages on the FMC has been filled out and there is no indication from the FMC or instruments of anything being wrong along the way (except for the missing change over and resulting overspeed).Anyone has any idea as to what I should try do next to resolve this issue?