Bug report: VNAV

[PilotAlpha]

i forgot to lower the mcp altitude for a good while (i think I overshoot my TOD by 6nm)

so when i decided to go down the fmc gave the message "DRAG REQUIRED"

with full spoilers and thr idle i was able to catch the vnav deviation pointer but what happened is that the plane was overspeeding by the time i was on glide according to vnav the plane crossed MMO which caused the SPD number at the MCP to blink suddenly the whole MCP started buggin out with blinking numbers in the SPD and ALT windows

 

had to go manual from that point on forwards

 

since those flights take so much of my free time I havent been able to reproduce the issue 

[Nils]

Hi, judging by your description, it sounds like you overspeeded and the Autopilot and Auto Thrust protection modes took over. 

In a situation like this you have consider adjusting your routing to extend the descent. I sure way to avoid the overspeed is also to select MCPSPD and only use the VNAV deviation pointer as a reference.

 

[Litjan]

Another way is to switch to FL CHG before overspeeding and then fly in FL CHG with high speed and speedbrakes until you are back on the vertical deviation pointer. Then you can engage VNAV again.

Jan