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dyszka89

Margin of error A/T

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What is the margin of error when the autothrottle disconnects during the approach? As for speed ...

Pretend that I'm flying at a speed VREF 155, but FMC handed speed 150. Does A / T to disconnect?

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It doesn't disconnect in that situation as far as I'm aware. IIRC you will get an A/T caution if the difference between actual and commanded airspeed is greater than 10 knots.

 

The FMC shouldn't command an airspeed less than Vref.

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Full names in the PMDG forums please.

 

Sure, you can set any speed you want in the MCP...; which brings up the question what is it that you are trying to accomplish?

 

A under/over speed selection error will be annunciated, for example A103. See FCOM 4.10.2

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I asked, because often my actual speed drastically different from the speed vref approach and I was afraid that one day it will lead to disconnect the A / T. Now I know what is the limit.

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I asked, because often my actual speed drastically different from the speed vref approach and I was afraid that one day it will lead to disconnect the A / T. Now I know what is the limit.

 

It probably won't underspeed. If you are over the commanded speed, you'll get a "DRAG REQUIRED" message in the scratchpad and/or an A/T yellow light, depending on your options.

 

It sounds to me like you're most likely getting fast on descent/approach. There are a bunch of threads that deal with that problem.

 

And if, for some reason, you were to get a disconnect of the A/T (haven't seen it except for failures) you should take over. I often intervene on the A/T. Most often, it's on descent with the A/T in ARM, but that's not all. Sometimes in cruise, you'll need to pull the throttles back a bit to prevent over speed. These probably aren't your situation.

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It probably won't underspeed. If you are over the commanded speed, you'll get a "DRAG REQUIRED" message in the scratchpad and/or an A/T yellow light, depending on your options.

 

It sounds to me like you're most likely getting fast on descent/approach. There are a bunch of threads that deal with that problem.

 

And if, for some reason, you were to get a disconnect of the A/T (haven't seen it except for failures) you should take over. I often intervene on the A/T. Most often, it's on descent with the A/T in ARM, but that's not all. Sometimes in cruise, you'll need to pull the throttles back a bit to prevent over speed. These probably aren't your situation.

It's what you write coincide. Tomorrow I will try to test my new knowledge into practice, I set myself the windy approach and see what happens. We thank you for your answers, I'll talk more tomorrow :)

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