TOGA - pitch and roll mode

[Tom Stian]

Hello

Since I dont know Ill try here again.

If you use TOGA for takeoff.
And lets say at 2000ft you engage CMD. Then the pitch mode will be LVL CHG and roll mode will be HDG SEL if you havent selected LNAV or VOR/LOC.

At the MCP the LVL CHG is ligthing up, but not HDG SEL. Is that correct?

 

[Litjan]

Hi Tom,

yes, this is correct - we had some discussion about this back then and I didn´t quite remember, but one of our beta testers checked it in the real aircraft. The HDG SEL is active, but the button isn´t lit.

Jan

 

[Tom Stian]

I see.

Wonder what the logic is behind that from Boeing. But I guess I have to live with it. 

Thanks again for your answer.

 

[Litjan]

I think the reason behind this behaviour is the "deselect" function of the pushbutton on the MCP. The take-off mode of the flight-director is basically FL CHG in the pitch channel with a complex algorithm to determine the target speed (V2+15 with both engines) and HDG SEL in the roll mode. This roll mode can not be deselected, though. So when you engage the autopilot, the pitch mode switches to FL CHG with a fixed speed, but the roll mode stays in HDG SEL (but can not be deselected - so no light on the button).

Just my guess why...

Jan