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Vref headwind correction on a CJ2?

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Vref headwind correction on a CJ2?

Old 9th Jul 2015, 14:36
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Vref headwind correction on a CJ2?

BizAv didn't really seem to be the right place for this question hence my posting it here.
In almost 2 years of flying a CJ2 I've only ever encountered one pilot applying a headwind correction to Vref and his background is the Regionals so that's probably where he picked it up.
Does it even make sense to do it for a CJ2 with a MLW of 11,500lbs?
What say you...yea or nea
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Old 9th Jul 2015, 20:18
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What does the book say?
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Old 9th Jul 2015, 22:20
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If I knew what the book said I wouldn't have to ask.....

* I'm not at the airplane right now and don't have a spare manual at home *

It wasn't covered during training at CAE that's for sure......
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Old 9th Jul 2015, 22:25
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I have seen quite a few people make Vref corrections for head wind. I do not understand why as it is totally unnecessary. You completely mess up your landing figures and you are carrying too much energy and just float when you should be on the runway and require the brakes to absorb more energy. In my view it is unsafe practice.

20 to 30 years ago most CFIT incidents were aircraft hitting the ground in the undershoot because of poor and unsafe practice. The result is that we now have a generation of pilots who think it is safe to approach high and fast. With out accurate figures to hand, now somewhere around 98% of CFIT are runway overruns.

It is best practice to come over the threshold at Vref with corrections for gusts only. This is by far the safest way to fly.

MM
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Old 9th Jul 2015, 22:36
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Originally Posted by lalbak
What does the book say?
The 'book' says nothing. This is a Cessna.
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Old 9th Jul 2015, 22:37
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Let's take a Vref of 104 kts for 10,000lbs.
Runway 060
Wind 080 10G20

So increase Vref with half the gust factor which would be 5 kts for a Vref of 109.

Why still add a headwind correction for the 9 kts headwind (continuous) or 18kts in the gust?



adding a headwind correction would (I assume) make sure your GS over the threshold is always the same regardless of wind conditions.
But hey, I'm not the smartest......
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Old 10th Jul 2015, 01:24
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CJ4: 1/2 HW + full gust. Max 20kts over Vref. The 510 was the same as I recall.
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Old 10th Jul 2015, 01:37
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L888

CJ4: 1/2 HW + full gust. Max 20kts over Vref. The 510 was the same as I recall.
Exactly the same on the B757, and I believe most / all Boeings...
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Old 10th Jul 2015, 03:57
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Vref headwind correction on a CJ2?

Miles, of course you calculate the LDR based on your expected groundspeed, or, with the increment added to Vref. No added risk for overshoot.

Good question on the need to do it for light(er) planes than airliners. Lower inertia, less affected by windspeed loss, to some extend. Dont know the answer though.
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Old 10th Jul 2015, 13:08
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CJ4: 1/2 HW + full gust. Max 20kts over Vref. The 510 was the same as I recall.
So with my earlier example +4 and +10 for a Vref of 118kts instead of 104?
That seems a little excessive.

Vref 104 in a no-wind is a GS of 104 and you're landing distance is taken from the table, let's say 2850'.
Now you have a 10 kts HW component with no correction on Vref your GS is 94 and your landing distance will be less then 2850', increasing your safety margin.

If you apply a HW correction and therefore increase Vref you are increasing your GS again and getting closer again to your original number of 2850'.

I don't understand the purpose of this practice.
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Old 10th Jul 2015, 18:48
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Scylla and Charybdis

BeN2 wrote:
I don't understand the purpose of this practice.
You are only considering the risk of overrunning the scheduled landing distance. The other risk is that of arriving over the runway with insufficient airspeed to conduct a proper flare. That situation may arrive due to an adverse gust, or due to the natural reduction of windspeed with height above ground. The reported windspeed (assumed in the calculation of landing distance data) is measured at (or corrected to) a height of 10 metres above the surface. The actual steady windspeed typically varies as the 1/7th power of height above the surface. The calculation of required landing distance data takes into account 50% of reported headwind component, and 150% of reported tailwind component.
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Old 10th Jul 2015, 20:11
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The purpose of the practice is to cater for loss of airspeed when you enter ground effect. Glider pilots know all about downwind turns.

It is possible that with a strong headwind and as you descend the headwind drops off dramatically in very the last last portion of the approach as the wind is slower at the surface than at a few hundred feet. If the wind drops off by 10 kts suddenly an aircraft could suddenly lose 10kts of speed as the aircraft will not accelerate instantaneously.

However if you increase your Vref you must adjust your landing calculations and most small business jet manuals do not have sufficient information to do this.

There is a very useful FAA paper on increased landing distances with higher Vref. One type I have flown states that for every extra 5kts over Vref LDR increases by 7% unfactored and 10% factored, it was a turboprop. Part Ops states that if you adjust your landing technique you must adjust your LDR appropriately. But you will not be able to do this unless it is software based as the calculations will be complex as you are not allowed to consider more than 50% of headwind for calculations etc.

Much simpler and safer to stick to the flight manual speeds unless you have a capable software package on the EFB which you use in flight.
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Old 10th Jul 2015, 20:37
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I can not find the FAA AC I was looking for but AC 91-79 has some good advice which indicates that arriving over the threshold at the correct height Vref +10 and touching down in the correct place will add approx 300 ft unfactored to LDR.

An extended float can add 2500' then wet runway, shallow angle and being above 50' over the threshold with power still applied will all add distance and very soon your LDR can be in excess of 3000' more than you calculated. This is not good.

Remember that the AFM figures are usually calculated for 50' over the piano keys with the engines at idle on a 3 deg glideslope. In a small business jet this will have you correctly in 3 reds 1 white (see tech log PAPI thread where some grown ups have posted some good advice) and touching down at Vref -7 to 10 kts. Any thing more and you are seriously increasing your LDR.

Stick to the book speeds.
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