Hi all, enjoying all of my newly purchased CS aircraft, but there is an issue with overspeeding on the 767 that I don’t have on anything else. Here’s my workflow and the issue. Any insight would be greatly appreciated!

1. FDs on, AT Arm, VNAV, LNAV on. Runway course set to HDG, V2 speed set to IAS/MACH dial.
2. Press TO/GA power setting on the buttons above flaps indicator.
3. Press SPD button to engage AT on takeoff.
4. Gear up, Flaps up on schedule, Engage Autopilot. Change power setting above flaps indicator to CLB. Then when at cruise, change it to CRZ.

Speed under control during climb in steps approved by ATC - change alt as required, pressing VNAV engages climb between steps.

Once at cruise, it just goes into overspeed despite FMC showing .801 as the speed setting in MCDU. Engaging SPD button to correct and roll speed back to .80 - nothing. Still keeps overspeeding.

The only remedy is to engage speedbrakes. About 1/2 speed brake gets me to Mach .80 which is fine.

Am I doing something wrong? Is this a bug?

Angel of Attack wrote on Apr 14^th, 2021 at 1:31am:



Thanks, I will try your flow later tonight. I do have FDs enabled and TO TO mode is shown, so that was always in line.

From my understanding, VNAV activation depends on airline policy - some airlines require it to be activated on the ground, and some give you a little more flexibility on that, but I am not positive that it's the case with a 767. The weird part is that I am not experiencing this overspeed issue on the 737 by CS, or the 757 by CS, or on any Boeings by another company, so this is something that has happened twice (both flights I have ever done on the 767) and it has me puzzled.

Even if the TO procedure is not exact, once I press the SPD button and preset my speed to .80, the AT should then adjust the power level down to get out of that overspeed condition, no? And if I am not in the SPD mode but in VNAV in cruise and I have the VNAV SPD annunciator lit up on PFD, it should really follow the setting from the FMC, no? It just seems that even if something during takeoff wasn't done 100% by the book, I should still be able to select SPD mode and it should reduce the power to attain the setting I have dialed in, right?

The weird thing is I don't really get this issue on descent. Once I begin descent, the speed management seems to not really be an issue, especially when I am getting close to final and gradually reducing the assigned IAS via the dial - everything is followed exactly as expected.

BostonJeremy77 wrote on Apr 14^th, 2021 at 4:00am:


Can you possibly take some screenshots of your MCP and PFD while this all happens?

One more interesting thing is that toggling VNAv seems to have fixed the issue on a subsequent flight. Just VNAV off, then back on. It started reducing speed.

I've definitely never had this issue. Can you save your flight right before takeoff and send the files? The .cs.config and the .fxml

G'day Alex, I have the files but unable to attach due to unsuitable file format. 

Cheers Steve

Didn’t see that inclusion  . One thing l did notice last night is that when l selected VNAV after t/o, the IAS immediately jumped to climb speed and disregarded the 250/10000 restriction

I just did that flight and VNAV (sort of) worked as expected. It didn't capture properly at 1000ft AFE but I believe that is a captain sim issue. Again most airlines don't allow VNAV selected on the ground on the 757/767 so I've never tried that before. I recorded a video and I'm uploading so you can see. One issue I would say is you had max takeoff power selected, which at that weight is a lot. I could barely keep up with how fast the airplane was accelerating (which you'll see I was late retracting the flaps). A de-rated TO-1 and CLB-1 would've probably been perfect.

Thanks Alex, haven't tried a de-rate departure as yet and may be the key as you say. Other issues l've found is the FMC calculated climb and descent speeds - way over the top so having to adjust those (i'm using 280/.78 as my default). Also getting a massive overspeed during the descent (around FL200) when using VNAV. I'll try the next one using FLCH.
Thanks for the help.

Cheers Steve

I have the same issue. I can't get the A/T to follow the profile. Normally you can set your cruise target speed either by entering the cruise mach speed in the FMS and use VNAV, or bypass the FMS cruise speed by using the speed mach mode of the A/T.

Neither method work, and what happen is that the A/T is chasing it's displayed EPR (in green) and not the target speed. I tried switching on/off/on various automation (VNAV, A/T, Speed mode, FMS entry etc.) but the A/T always chase the EPR limit and not the target speed.


I also tried to put the trottle either in min/max and hitting F1 or F4 to syncronize, put less sensivity and more deadband in the throttle calibration, but it didnt change nothing. If the A/T is on it will always put the aircraft in overspeed

I am at loste here...

fowler wrote on Oct 22^nd, 2022 at 3:28am:


Can you make a video or screenshots of this here?

That's wierd

Alex in your real sim scenario you talk about applying max power (is it max CONT ?) from a low speed situation at altitude. I talked about starting from the same situation but with applying very minimal increase of thust (let's say from 1.20 to 1.21 EPR) and seeing the aircraft accelerate far too long. It's not only the duration of acceleration which is the issue it is also the increase of acceleration. It seems that the rate of acceleration goes higher which is the part I find unrealistic. For any excess thrust applied in level flight there is an acceleration in speed that must be dampened. i.e. the rate of this acceleration is diminishing) due to squared function of air resistance. I have no idea of what the final accel will be on any scenario this must be shown on aircraft perf. manual or engine data.