What is ground speed mini ?

[javelin]

Before this spirals out off thread, our recent tailstrikes on the single aisle aeroplanes were when manual thrust was employed...............

Does that say we are out of practise, does it concur with Airbus findings about FBW degrading pilot skills, I don't know.

[Nessus]

I’m pretty sure I do understand how Ground Speed Mini works. Nevertheless a few questions linger, I would appreciate if you would bear with me. I don’t have any jet experience, perhaps these things would be self-evident if I did...

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Question 1. With Ground Speed Mini doing its job, why does minimum target speed (Vapp) need to be as high as Vls+15 in cases of a strong reported headwind?

In any case Ground Speed Mini will increases the target airspeed based on the headwind component. Thus sufficient energy would be ensured even when the minimum target speed is Vls +5. Why does one need the additional 10 kts of margin (in some cases) when Ground Speed Mini is there?

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Question 2. Isn’t there a chance that Ground Speed Mini can result in too much energy (too high airspeed) during the flare?

Landing RW 09. Tower Wind: 090/10. Vls: 130 kts = Vapp 135 kts.
Now, let’s say that instead of the reported tower wind of 090/10, there is a gust during the flare of 090/40. Target airspeed during a gust of 090/40 will be (Vapp + actual hwc – tower hwc) = 135+40-10=165 kts.

So, even though the groundspeed is fine in relation to landing distance available, target airspeed (which is a measure of energy) will still be 165 kts, 35 kts above Vls. If the pilot (or autopilot) maintains the target airspeed, won’t this lead to a prolonged flare, or worse – ballooning during flare?


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Question 3: Does the speed target change at 400ft AGL?

In a different thread someone explained that Ground Speed Mini changes the way it works below 400ft AGL. Above 400ft it adds the entire headwind component (- tower wind) to Vapp, but below 400ft it apparently only adds 1/3 of the headwind component.

Is this really the case? I haven’t been able to find anything about this change of behavior at 400ft in the FCOM.

It would be great if someone could provide a reference to the page in the FCOM where this change of behavior is explained.

If this is the case, I guess it would mitigate the problem with a too high airspeed during flare.