ILS cancellation

[danhenri]

Sorry if this question has already been asked. Is it normal that, on approach and fully established on an ILS, the APP Mode can not be disconnected ? For example, when APP mode engaged, I cannot switch to HEADING or ALT HOLD, even if I disconnect the Auto Pilot and try again. Yesterday, I wanted to do a visual circle rwy 36 on LFLB, and before, follow the ILS 18, then turn heading 135° on the left, stopping the decent at 1880 ft : the only way to do it is to engage VOR/LOC mode and VS mode to descend on the glide slope.

Thanks for your answer and assistance.

Edited May 31, 2020 by danhenri

[Litjan]

Yes, this is correct - as long as the FCC (flight control computer, either AP and/or FD) is in APP mode, it can not be deselected or other modes engaged. This is also signified by the light in the APP button extinguishing when the mode engages in both LOC and GS. It is a safety feature.

The way you did your ILS followed by a circle to land is exactly right. Use VOR/LOC and VS and then you can switch to HDG SEL and ALT HOLD for the break-off.

Alternatively you can fly the ILS in APP mode, but will have to disengage the FCC (both AP AND FD) to fly the break-off (you could engage the AP at that point again).

A very remote possibility would be to toggle the GA mode and then change to ALT HOLD and HDG SEL out of that - but that is a violent maneuver that you would not really do in the real aircraft.

Cheers, Jan

 

Edited May 31, 2020 by Litjan

[danhenri]

Thank you very much ! 

Have a nice sunday, Jan.