LDG/Conf Apr SPD/LDG Dist Folowing Fail.
 

During the last revision , Airbus decided to insert values to DRY , WET and Contaminated runways. QRH 2.32

Question:

Why the figures we have to multiply by the Actual LDG DIST are greater for dry runway than for wet and Contaminated?

Safe Flights,

A-3TWENTY

Because the wet & contaminated figures already have large margins applied to them compared to the dry...in the non-normal case these margins may not necessarily be appropriate any more.

Try putting some numbers through and you'll find that the LDRs for wet and contaminated rwys in the event of a failure are still greater than that required for a dry rwy. The reason it 'looks' wrong is because airbus keep the same process of landing distance calculation regardless of a/c or rwy condition - the only number that matters is what comes out at the end!

Also, Wet and Contaminated runway landing distance factors assume the use of all available reversers.

Planning to land on a wet rwy with dual (G+Y) hyd failure. (Sim time!)

From the QRH for msn 2500ish I came up with ALD (wet) 1360m with QRH wet landing correction factor of 2.15 to get LDR of 2924m.

For dry however the figures are ALD 1070m x dry landing correction factor 2.80, LDR = 2996m (3000m in QRH dual hyd fail summary) This doesn't really make sense to me.

Can someone explain or have I completely overlooked something??

In our co manuals it is stated that the wet figure can be less than the dry figure, so in our perf manuals there is a restriction that wet perf cannot be greater than dry perf.

In the event of such a failure then you must request CFR hose down the runway.

Just kidding.

Hi Boomerang,

With G & Y hyds fail, you'll be limited to 1,000 psi brake pressure to prevent the tyres from skidding due no anti skid.

1,000 psi wheel braking force is a fraction of what you might have been able to apply on a dry runway without the tyres skidding - so the wet & dry landing distances are very similar.