[AP] Probable Bug when opening the SPD Window during VNAV descend

[oMrSmith]

Opening the SPD window during VNAV descend does not engage the thrust mode "SPD" hence no thrust is added in order to increase IAS to the MCP target speed.

[prokopiu]

I had a similar behavior yesterday during my test flight but was not sure if I made something wrong. I will test this again this weekend.

[mSparks43]

Opening the SPD window during VNAV descend

looks like maybe missing the 15/20 kt part of FPE in VNAV descend

[oMrSmith]

This may also be the case. But what I mean is when you go manual SPD during VNAV descend.

The picture is referring to how VNAV behaves while the MCP window is closed.

[mSparks43]

then do you mean VNAV SPD rather than thrust mode? At the moment there is altitude lock on that, I cant see the part in the fcom at first glance, but I'm pretty sure its because at low altitude its locked into PTH and the throttle is in Hold (displays idle because its idle)

The full set of notes:

[oMrSmith]

So currently opening the SPD window during VNAV descend does not trigger VNAV SPD.

That's fine with me!

But if pitch doesn't control speed, then the thrust has to, as I would suppose...

[mSparks43]

So currently opening the SPD window during VNAV descend

both, I think I defined "on approach logic" active as "above speed restricted altitude". So above that, opening speed intervention switches it to VNAV SPD

Below that it stays in PTH, but you have the throttle (IDLE/HOLD) - bug here being it should take the throttle back and switch to SPD if you let the speed drop 15/20kts below the speed you set.

If you set the speed lower than the current speed, it should switch to VNAV SPD to slow down.