Autothrottle disconnection after pressing the LOC switch

[coceoca 0]

Hello together,

 

in my today's flight, the following happened during the descent phase:

 

After I've pressed the LOC switch to arm the LOC lateral mode, the autothrottle was disconnected (immediately upon the switch actuation).

I had the AUTOTHROTTLE DISC message and the acoustic warning.

 

Has anybody an idea why the autothrottle was disconnected upon the arming of the LOC mode?

 

I use a Saitek throttle quadrant button for disconnecting the autothrottle. However, this button seems to be ok.

 

Thanks for your thoughts.

 

Jens

... I just want to inform you, that I've clicked on the LOC button with my mouse.

[Budbud 227]

Hi,

 

There are a couple of conditions in which the autothrottle will disconnect automatically, there are described in the FCOM v2 p 4.20.9.
However in your case, only one would be plausible: a fault detected in the active autothrottle mode (failure).

 

_ When this occurs, in which position are the A/T arm switches?

_ What is displayed on the FMA before and after the alert is displayed?

_ Check you have no failure active.

_ Do you use a hardware for the throttles and how is it configured?

_ How is set the A/T manual override option?

 

Otherwise, one of your hardware must send a command to disconnect the autothrottle anyhow.

 

By the way, one rule in that forum is to sign your posts with full names.

[coceoca 0]

Hello Romain,

thank you for your answer. I've read 4.20.9 before posting:

- A/T manual override option was set to IN HOLD MODE ONLY   -> thrust levers were not manually overwritten

- reverse thrust levers were in the idle position

- A/T arm switches were in the ARM posision

- failures were disabled

 

Unfortunately I do not know anymore, what has been displayed in the FMA before and after the alert.

 

My hardware button for disconnecting the autothrottle is 100% reliable (or was 100% reliable up to now...).

 

The thing that could indicate that there might be an issue with the software is that the autothrottle disconnection occured in exactly that moment when I pressed the LOC switch.

 

Kind regards

Jens Müller-Junker

[Budbud 227]

Hi,

Try to reproduce it and log as much info as you can regarding your aircraft condition (FMA display, A/T mode, FMC config, speed/speed setting, flaps...).

It may be a software issue but also (no offence) a user issue.

If the problem occurs everytime you can also submit a ticket on the support website.