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3 Answers

Relationship between Vref and Headwind component

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General Aviation

Hello. I recently had a chance to talk with a retired commercial pilot, and he taught me I need to add a half of the headwind component and the whole gust factor of the reported wind to a Vref. I understand the reasoning behind adding the gust factor to a Vref, but I can't figure out why any headwind component should be added to it. It's true it takes a greater power(thrust) not to be pushed back on the final approach course when there are strong headwinds, but do I also need a greater Vref speed? I guess it only applies to big commercial jets? 

3 Answers

  1. Dave M on Jun 22, 2017

    As far as I know, Vref is Vref and commercial operations do not add anything for headwind. They will likely add 1/2 the guest factor, however.

    The only thing I would guess about adding a headwind component might be to keep your descent rate similar while staying on glide slope, or PAPI/VASI (i.e. greater headwind=slower ground speed=slower descent rate).

    I’m not exactly sure what the real benefit is, though.

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  2. Jim F. on Jun 24, 2017

    Never heard of adding any of the straight headwind component. That being said, my 121 airline’s SOP is to add a minimum of 5kts to Vref to “prevent airspeed excursions below Vref while ensuring reasonable pilot workload.” A 10kt addition is our maximum allowed,, which will generally account for the classic ‘half gust factor’.

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  3. Best Answer

    Ray Salmon on Jun 25, 2017

    Several transport category aircraft AFMs have procedures/recommendations for adding 1/2 the steady-state wind and 100% of the gust factor. Airbus aircraft even have a built-in function called Ground-Speed Mini that actively increases/decreases the bugged speed in response to the sensed winds on final approach to maintain a steadier ground speed.

    The reason behind it is that wind speed generally diminishes with altitude due to surface friction. Using an additive helps to mitigate the loss in performance resulting from the loss of headwind close to the ground resulting in a more stable approach from a performance standpoint.

    Problems start to arise when you have a high steady headwind component coupled with a large gust factor. Most AFMs have an upper limitation to the additive of around 20 knots, but unless you start to pull back the speed so you\’re close to a no-wind Vref around touchdown, even 20 kts can extend your landing distance considerably. So the recommended practice is to bleed your additive off so you touchdown around Vref.

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