Confused about Flight Director

[Vespa]

Sorry for the silly question...but I'm a bit lost and confused about the Flight Director system of this great aircraft.

Expert will be laughing but, eveen after viewed the video tutorial I'm not sure to understand exactly the purpose of the two switches...I mean, in Ian's video I see Auto Trhust working as expected even if F/D is not switched on...same for autopilot A and B...they works in all different modes without F/D switches moved to on.

So, could you please explain why I need to switch on Flight Director switches?

Thanks a lot for any feedback 

[Litjan]

This is in fact quite complex.

The autothrottle will work without the flight director. You can use it in N1 (full power) and MCP SPD mode. Just push the corresponding buttons on the MCP. It is also dormant (when armed) to trigger when the TOGA buttons are pushed or when the speed protections kick in.

To actually have the autothrottle work in the COMBINED modes, you need to have the FD or AP on. Then - if a COMBINED mode triggers, the autothrottle will respond as well.

For example: You push the FL CHG button on the MCP. This is a COMBINED mode which will engage the pitch mode (of FD or AP) to maintain the speed set on the MCP but will ALSO (thats why its combined) trigger the autothrottle to go to N1 (for the climb) or RETARD (for the descent).

Cheers, Jan

 

[Vespa]

Thanks a lot Jan.

So the keyword is: COMBINED: to get Auto Thrust engaged and working with other COMBINED mode selected on MCP I have to switch Flight Director ON.

And how about the purple bars on EADI?.

[Litjan]

The purple bars ARE the flight-directors. Of course you need to turn on the FD switch to see those - but they will only show if they also "direct" something. In other words - you need to have a mode working for them to direct you.

For example you could only have HDG SEL engaged - then only the vertical director bar would show...since there is no pitch mode "directing" (no horizontal bar).

Jan

 

[Vespa]

Thanks a lot for the invaluable support and feedback Jan ... as usual.

I have to learn a lot more about this great aircraft.

Edited December 28, 2019 by Vespa