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Smilencio

Minimum Approach Vref=137kt?

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I have notice this for a long time...

 

As shown in the picture, GROSS WT is no more than 398000 pounds, with no passengers, no cargo, only about 53000 pounds of fuel. but 30/137 is obviously too fast for the plane. If I perform an approach with this value, I will get a negative pitch. So the approaching speed I have been referring to all these days is the speed 10kts above the yellow line when flap is set, and this speed will give me a perfect pitch when approaching. However occasionally I can see the Vref provided in the FMC is correct, just like my own calculation-- about 10kts above the yellow line, but still I see 30/137 more often. I still can't find the factor that make the difference. Am I doing something wrong or is this something to be fixed in the future..?

 

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Yep, Vref won't go bellow 137, you can use smaller flaps if light.

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I read that this is a feature of the 777s with the 110/115 engines, something about the extra thrust compared to the other engine variants and maintaining a safe speed over some V speed of the sort. I know, helpful right lol.

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Shooting from the hip, but it may relate to VMU. V-Minimum Unstick Speed.

 

 

 

Vmu (Minimum unstick speed): Minimum airspeed at which airplane can safely lift off ground and continue take-off. Because of the way this speed is determined, lift-off is not possible prior to reaching this speed

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The OP is talking about Vref on approach. 137 knots on the LR is related to Vmca (minimum controllable speed) in the event of a single engine go around.

 

it is called the Vref Floor

 

Regards

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Ah yes. Copied. That's what you get from not reading the post properly and firing from the hip. lol...not long woke up from a Red Eye YMML -YPPH and return....I'll crawl back in my hole.... :blush:

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Hehe, well it was a good guess ;) 137 knots is also minimum V2 so it does also apply to the take off phase

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Yeah, I started a topic on this very thing a while ago. Because the engines are so powerful, there is a min controllable speed of 137 if a engine out occurs. A real world pilot responded by saying that the real vref at almost empty weight would be around 115-120, but the airplane would not be controllable at that speed. If you look at the VRef speed at max landing wait on the passenger version, it is 138, which goes to show just how effective the wing and flaps are. For me personally, if the Vref difference between flaps 25 And flaps 30 is 5 knots or less, then I use flaps 25

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Going faster than the true Vref is extremely common in the real world too. 20+ knots is often added onto the calculated Vref due to windshear in the area. (ie Narita when they get the crazy winds in March) 

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