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?

Your T/O flow is wrong. however I doubt that along would cause real aircraft to overspeed. I thinke Real Boeing would have more thought about how the AP would behave when mishandled.

Try the proper flow to see if that works:
1.For 75/67, VNAV should NOT be armd on ground for TO
2.TO/GA button on TMSP should be select on pre-flight flow even before doors closed and engine started, but it's OK-ish to press here.
3.after lineup with runway and cleard for T/O, you should manually throttle up to about 1.1EPR, let the engine stable, and then press the EPR button above SPD button to engege AT.
  also, make sure you have turned F/D on on the ground, and the FMA shows       | TO | TO , before taking off.
4.Gears up, at Thrust reducing Altitude (above 400' at least, but normlly at 1000' , or 1500' for NADP), press VNAV or FLCH, the thrust mode should automaticly change to CLB, no need to press button on TMSP. lower the nose for speed up and retract flaps on schedule at accl alt.

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

Your T/O flow is wrong. however I doubt that along would cause real aircraft to overspeed. I thinke Real Boeing would have more thought about how the AP would behave when mishandled. Try the proper flow to see if that works: 1.For 75/67, VNAV should NOT be armd on ground for TO 2.TO/GA button on TMSP should be select on pre-flight flow even before doors closed and engine started, but it's OK-ish to press here. 3.after lineup with runway and cleard for T/O, you should manually throttle up to about 1.1EPR, let the engine stable, and then press the EPR button above SPD button to engege AT.   also, make sure you have turned F/D on on the ground, and the FMA shows       | TO | TO , before taking off. 4.Gears up, at Thrust reducing Altitude (above 400' at least, but normlly at 1000' , or 1500' for NADP), press VNAV or FLCH, the thrust mode should automaticly change to CLB, no need to press button on TMSP. lower the nose for speed up and retract flaps on schedule at accl alt.

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.

Ok, just tried your workflow for TO and the same thing is happening with overspeeding. I am at a loss. It’s not a complete deal-breaker, but it’s less than ideal having to fly on speedbrakes the entire cruise. Considering this doesn’t happen with any other aircraft, it makes it less appealing for me to fly the 767 unless I can get it to stop overspeeding.

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

Ok, just tried your workflow for TO and the same thing is happening with overspeeding. I am at a loss. It’s not a complete deal-breaker, but it’s less than ideal having to fly on speedbrakes the entire cruise. Considering this doesn’t happen with any other aircraft, it makes it less appealing for me to fly the 767 unless I can get it to stop overspeeding.

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

This is what I have from the latest flight.

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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'm also having the same issue. I followed the procedure as per your instructions but it climbs like a rocket and accelerates to 300+kts in no time flat. I can bring it under control fairly quickly but not ideal, particularly with the 250/10000 restriction.
It's possible I've missed a step but am at loss to know what that is.
Any assistance greatly appreciated.

Cheers Steve 

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

The files as requested

Cheers Steve

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

Cheers Steve

In a zip?

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

Files as requested

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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.

Just noticed in your CDU that the first pseudo waypoint of 800ft MSL was missing, I reselected the SID to get it back in there. Not sure if you deleted it or what, but it was causing a confusion to the VNAV.

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

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I noticed that as well! You do have a pretty high cost index (they need to fix this too) I saw the weird speed in the CDU LEGS page so I reselected the SID the climb speeds went back to normal.

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...

Another weird thing is how the aircraft react to thust change when A/T is off. In cruise when you do a very slight power up adjustment you can see the aircraft constantly accelerate for 10' minutes long and more. I got from 0.82 mach to 0.86 mach in more than 15 minutes with a very limited power change when I was stable at 0.82 mach.

This is really unrealistic because the air resistance is not a linear function but a square function of speed. And that means that for a slight power change you should see a slight speed change rapidly that get amortized quickly and settle in the next equilibrium state of power/drag ratio. There should't be a large change of speed at a low rate how it occurs here.

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

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...

Can you make a video or screenshots of this here?

fowler wrote on Oct 22^nd, 2022 at 3:49am:

Another weird thing is how the aircraft react to thust change when A/T is off. In cruise when you do a very slight power up adjustment you can see the aircraft constantly accelerate for 10' minutes long and more. I got from 0.82 mach to 0.86 mach in more than 15 minutes with a very limited power change when I was stable at 0.82 mach. This is really unrealistic because the air resistance is not a linear function but a square function of speed. And that means that for a slight power change you should see a slight speed change rapidly that get amortized quickly and settle in the next equilibrium state of power/drag ratio. There should't be a large change of speed at a low rate how it occurs here.

I'll have to admit that I don't agree with this.

In real life, I fly an airliner which weighs a bit less than the Boeing 767, but has a very similar thrust to weight ratio. This is one of the scenarios we do in training to show the lack of excess thrust in high altitudes. In the another company simulator, we start at 250KT/0.75M at FL350 more or less, then we set the thrust to max power and see how long it takes to get to 270KT/0.80M, and it generally takes 90-120 seconds. If this is at MAX power, it almost makes sense that a slight power change would cause a 0.04M increase in 10 minutes. This issue isn't as much air resistance but lack of excess thrust. If you have excess thrust, yes it will equalize at a particular speed because of the exponential increase in drag, but how do you know how that is with a PW4060 at FL350 at 300,000lb, for example?

That's wierd

I only did two flight with this new B767 and couldn't lock the A/T to either follow the speed mode (in mach as I'm talking about the cruise portion) or the VNAV mode. (Both modes set to M082.

In fact the reason of the "infinite acceleration and thus overspeed" comes from the fact that the A/T constantly goes for max cruise setting (displayed in green) which is way to much and will result in a overspeed.

BTW I tried it with the B757 on the same flight and I have the exact same issue.

Does it work for you Alex ?

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.

OK I think I found the issue I have, it has to do with my joystick. Once in cruise I unplugged my joystick and immediately the A/T was nailing the commanded speed. I also tried some speed change (M082 to M080 to M082) and the A/T responded immediately and nailed the new commanded speed) Strange I calibrated my joystick but I suspect a "drifting" button somehwere interfering with the A/T.