Airbus Vapp

[longobard]

What's the minimum Vapp in case of Headwind 9kts, no Icing, ATHR OFF?

Vls+3 (1/3 Headwind) or Vls+5?

According to Operating Speed definitions in the airbus supplementary techniques the The wind correction is limited to a minimum of 5 kt

[MCDU2]

It's in the QRH under vapp determination. 3 kts in your case. Would be 5kts if you left in the a/thr. Just work through the table.

[longobard]

It s in FCOM PRO-SUP-10
The wind correction is limited to a minimum of 5kts

Does this mean that from 1 to 15 kt headwind the wind correction has to be 5kt or that unless you have at least 15kt headwind your Vapp is equal to Vls?

[john_tullamarine]

Folks,

You're missing the philosophical point.

It's not a matter of surgical precision and if you're half a knot off the sky is going to fall down and Chicken Little goes around the twist.

Doesn't matter which colour aeroplane you are flying -

(a) steady wind correction addresses the known and expected near surface wind gradient which, in general, is approximated by a fairly standard formula

(b) gust corrections address a random event in respect of which the pilot has little influence.

There are several threads on the subject which are worth revisiting. This thread (http://www.pprune.org/tech-log/485837-wind-additives-landind-speed.html) is useful as it has additional links to others.

[longobard]

John... sorry but we are not talking about half knot. .

According to one interpretation of airbus publication there might be the chance to consider no wind correction for a steady 14kts headwind.

That's out of the basics!

[vilas]

longobard
Principally what John has said is correct, however in Airbus FBW gust is automatically taken care of by ground speed mini so pilot doesn't add any correction for that. For 14kt headwind Vapp should be Vls+5. Why should there be no addition? 1/3rd has two limits zero in case of nil or tail wind and max 15kts.

[longobard]

Vilas
as stated in the fcom reference above the lower limit of wind correction is 5 knots

0 can be used only in case of no wind, no athr, no ice accretion

[nitpicker330]

The Airbus FM automatically adds 1/3 the headwind onto the VLS to give you it's own VAPP.
Minimum 5, Maximum 15.

[vilas]

longobard
That is what I am saying, with 14kt headwind why should there be zero correction?

[I-2021]

The concern that longobard is raising deals with the fact that, according to his first example, with a headwind component of 9 kt and no ATHR/Icing the Vapp as x QRH would be VLS+3 kt. In the definition of Vapp in the supplementary procedures (Operating speeds) the minimum wind correction to add is 5 kt, hence in that scenario the Vapp would be VLS+5 instead of VLS+3. Basically according to that we can say that an approach with no wind at all could be flown at VLS whilst an approach with at least 1 kt of headwind component should be flown at VLS+5. I believe it is a discrepancy in the way the information is written up.

[WhyByFlier]

You can approach with Vls to land. See note 1 under the table in QRH where it says:

'' In case of strong or gusty crosswind greater than 20kt, VAPP SHOULD be at least VLS + 5 kt……''

You're correct, characteristic speeds does say wind correction is limited to a minimum of 5kt but I think that is referring to the logic of the FMGC - I think, I do not know.

We had an airbus recommendation within our company (easyJet) that Vapp SHOULD be increased to Vls+5kt if it ever shows as less on the PFD.

I'd fly VLS+5kt as a minimum in normal operations.

Nowhere does it say we MUST.

[longobard]

Vilas

0 wind correction for 14kts headwind is of the two interpretations:

Since your minimum wind correction should be 5kts, and since the wind correction is 1/3 of headwind, then the minimum headwind to be considered to calculate wind correction should be 15kts

I don't believe this is a physically correct interpretation but is one the thousands that this magnificent aircraft delights us of...

[vilas]

longobard

VAPP COMPUTATION (from FCOM DSC Auto flight)
VAPP, automatically displayed on the MCDU PERF APPR page, is computed as follows:
‐ VAPP = VLS+1/3 of the TWR HEADWIND COMPONENT, or
‐ VAPP = VLS +5 kt, whichever is the highest.
From PROSUP Operating speed definition.
VAPP : Final approach speed. Displayed on MCDU APPR page.
Calculated by the FMGCs.
Represents : VAPP = VLS + wind correction
The wind correction is limited to a minimum of 5 kt and a maximum of 15 kt.
The flight crew may modify VAPP through the MCDU.
‐ During autoland or when A/THR is on or in case of ice accretion or gusty
crosswind greater than 20 kt, VAPP must not be lower than VLS +5 kt
FROM QRH
Approach correction : 5kts (only in case of ATHR ON) +1/3 Headwind(MAX=15kts)
So your statement is true if you are using FMGC calculated speed i.e. no addition is required upto 15kts HW but you can use Vls for approach if auto thrust is OFF and in nil wind. This is splitting hair but technically correct.

[longobard]

Agree! Thanks!

[flyboyike]

Folks,


You're missing the philosophical point.

It's not a matter of surgical precision and if you're half a knot off the sky is going to fall down and Chicken Little goes around the twist.

Doesn't matter which colour aeroplane you are flying -

(a) steady wind correction addresses the known and expected near surface wind gradient which, in general, is approximated by a fairly standard formula

(b) gust corrections address a random event in respect of which the pilot has little influence.

There are several threads on the subject which are worth revisiting. This thread is useful as it has additional links to others.


John, old chap,

If everyone used such a common sense approach at aviation as you advocate, what would be the use of this forum? Besides, where are all the simmers (whose presence around these parts you and other mods so strongly encourage) get this common sense?