September 5, 20169 yr 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?
September 5, 20169 yr 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.
September 5, 20169 yr Author commanded airspeed Thanks for the answer As for the speed entered in the MCP?
September 5, 20169 yr 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 Dan Downs KCRP
September 5, 20169 yr Author 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.
September 6, 20169 yr 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. Matt Cee
September 6, 20169 yr Author 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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