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bradrcfii

VNAV Path question

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I flew the KLAX Seavu STAR last night and sat back and watched the NGX hit every single altitude restriction right on. Very impressive. I did notice FMC Speeds that I do not know where they are coming from. At one of the fixes, the legs page showed 187 at this fix while the magenta speed was 206 above the speed tape(still in VNAV). I am assuming the FMC is indicating 206 is necessary to stay on path as I could not reference this speed anywhere in the FMC.Is my assumption accurate?


Brad Rich
 

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I flew the KLAX Seavu STAR last night and sat back and watched the NGX hit every single altitude restriction right on. Very impressive. I did notice FMC Speeds that I do not know where they are coming from. At one of the fixes, the legs page showed 187 at this fix while the magenta speed was 206 above the speed tape(still in VNAV). I am assuming the FMC is indicating 206 is necessary to stay on path as I could not reference this speed anywhere in the FMC.Is my assumption accurate?
187 is below the F0 maneuvering speed. The FMC won't slow you below that unless you are configured for the predicted speed. Were you at F1 (or F5, maybe)? Or your guess could be correct.

Matt Cee

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187 is below the F0 maneuvering speed. The FMC won't slow you below that unless you are configured for the predicted speed. Were you at F1 (or F5, maybe)? Or your guess could be correct.
Good point. I believe I was clean. In fact, 206 was probably Flaps Up minimum speed.

Brad Rich
 

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Brad,Here's how it works - the NGX barring any other restrictions will shoot for being at the Flaps 40 maneuvering speed plus 20 knots right around the glideslope intercept point. This ends up being the same thing as the Flaps 15 maneuvering speed. The point at which it begins slowing down to reach this speed depends on the path and which restrictions are there. If there's a lot of restrictions and steep path segments, it will start trying to slow down pretty far out.During the slowing process, the plane will stop at each maneuvering speed and then decelerate further after you put the required amount of flaps out. It usually stops somewhere around 210-204 or so depending on weight with no flaps out and then continues on down from there. Normal flap deployment schedule is 1, 5, 15, 30 and then 40 if 40 is selected for landing. Flaps 2, 10 and 25 are just "pass through" on a normal landing, they're never selected on their own. (this info all comes out of the FTCM procedures)


Ryan Maziarz
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