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Hello,

Could someone explain me how the A/T switch should behave in a real 737-300.

- When can it be switched and stays on during normal operation?

- Does/can it disengages itself if something happens? If yes, what shall happen?

Thanks in advance.

Cheers

Sylvain

 

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Hi Sylvain,

the autothrottle system is very complex and can´t be explained in a few words. Google for a real 737 FCOM (there are plenty out there) and read up if you want to know the whole story.

If you just want to know how to use it "normally" I would suggest watching and re-flying the tutorial videos I made for the 737.

Cheers, Jan

 

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Hello Jan,

I have read the FCOM and found how it is supposed be used and not used.

It is indeed quite complex and I am far from understanding it fully :-)

 

Maybe my question was unclear, so I'll try to be more precise:

I am focussing only on the A/T ARM switch on the MCP.

As it is a solenoid switch, there should maybe be some circumstances where it will not accept to be switched ON or where it will switch OFF automatically.

As far as I could read/find until now, it will switch automatically OFF when the pilot presses the "A/T disengage" button on the throttle lever.

But is this the only circumstance where the A/T solenoid switch will automatically be deactivated?

It seems that it will always accept to be activated.

Cheers

Sylvain

 

Edited by Syl20

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Hi Sylvain,

you would turn ON the autothrottle ARM when entering the runway for takeoff. Not earlier, so if you accidentially touch the TOGA buttons while taxiing around the airport you don´t want the engines to go to takeoff thrust.

The autothrottle should ALWAYS stay in ARM (never turn if OFF) during the whole flight. This guarantees that it is ready to jump into action when needed (pressing TOGA, getting too slow, going to MCP SPD when changing the pitch mode, during ALT AQC, for example).

The autothrottle will automatically revert to OFF 2 seconds after touchdown, not pilot action needed.

Recently this was changed: Boeing now allows to turn the autothrottle to OFF if the pilot does not want the "combined modes" - for example when capturing the GS or when going to ALT AQC, the autothrottle will automatically engage in MCP SPD. This requires the pilot flying to command "disengage SPD mode!" to the pilot monitoring repeatedly, so Boeing allows to turn the autothrottle to OFF when flying manually. It is undesired system behaviour, so to say.

Cheers, Jan

 

Edited by Litjan

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Many thanks for these information Jan, always a pleasure to learn some more :-)

Cheers

Sylvain

 

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