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Just a little confuse when I learned about the aircraft classification based on approach speed. Can anyone help me to have an accuracy look about this question?

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Vref is indeed defined as

Landing reference speed or threshold crossing speed.

It is normally set with reference to Vs0 which is stall speed in landing configuration. Vref must usually be greater than 1.3x Vs0.

By way of example, the POH for my PA-28 lists the stall speed with flaps down (ie. landing configuration) as 45KIAS. I tend to be around 70KIAS on final approach and 65KIAS over the threshold. 1.3x my stall speed would be roughly 59KIAS, so I have about 5KIAS safety.

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  • $\begingroup$ For an airliner, the target for the threshold crossing speed is typically 5 to 15 knots higher than $v_\text{ref}$, depending on headwind. $\endgroup$
    – Bianfable
    Oct 13, 2023 at 11:08
  • $\begingroup$ @Bianfable It surprises me that its not represented still as a factor of vref $\endgroup$
    – Jamiec
    Oct 13, 2023 at 11:09
  • $\begingroup$ Since it's related to wind, I guess they add because the wind speed is additive to the airspeed, but not sure. Airbus has a lengthy article on the topic (search for "Lowest Selectable Speed" and "Approach speed" for the relevant parts). $\endgroup$
    – Bianfable
    Oct 13, 2023 at 11:20

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