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Guest RobC

737-800 FMC Speed Control

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I am currently flying the 737-800 and have been unable to override the FMC speed contols during the approach to land. Consequentially, the plane is flying at a speed of 280kt on approach. How do you override the FMC?

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There are several ways you can change your speed settings.1 - The best way is to program the FMC to reach a certain waypoint at a certain speed. Simply select the 'LEGS' page scroll through the waypoints and on the right of the waypoint where you can see the Speed and ALT planned for the waypoint, change it by simple typing the desired speed into the scratchpad and pressing the relevant Line Select Key on the right. e.g if you want to arrive at waypoint at 180kts, type 180/ and select the relevant line.2 - On decent you can select the SPEED button on the MCP and manual select your speed and use the V/S to ensure your select altitude is met by using the green moving "BAR" on the ND.3 - Also if you want to continue using the VPATH of the FMC then continue with VNAV selected but use the SPD INTV button to select your speed.As mention the easiest way i find is to program your speeds into your FMC. Makes it alot easier for planning your decent.Hope that helps, am thinking of the top of my head so if there's a mistake please correct me!!

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You can also use other modes than VNAV once you have started your descent. Hit the LVL CHG button, and turn the speed knob until it's at the speed you want it to be, and the rest LVL CHG will take care of by applying minimum power (Flight Idle) and adjusting pitch to maintain the speed. Once you're at something like 3000 feet what I do is disengage LVL CHG or VNAV and enable Alt Hold and set the speed to 200-180 while adjusting flaps as neccesary.

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If you use LVL CHG your current speed is your target speed. So first set the speed in MCP an than push LVL CHG. Why disengage LVL CHG? At target alt the mcp level the plane out.What about the INIT page? Have you set your current flap setting for the approach? Stefan

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If you want to override the FMC, you can also disengage the VNAV mode and set a target speed and altitude. You can use the LVL change to decrease your speed, and do not forget to select your landing flap mode (into the FMC / INDEX / APPROACH) and to arm the ground speed brakes.When landing, it is mandatory to set the throttle on "idle", if you want the spoilers to deploy, and if you want to avoid an annoying alarm ring bell.Regards.

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