A320 QRH - Dry ALD > Wet in ELEC EMER CONFIG

[nnc0]

Having studied and worked in Performance Engineering in an earlier life I'm embarassed to ask this here but so far I've had no luck explaining the following Actual Landing Distance (ALD) anomaly:

Between the older and newer models we have 5 different groups of A319s, A320s and A321s.

With regard to the ELEC EMER CONFIG checklist from Abus
4 fleets shows the ALD (DRY) < ALD (WET).
1 fleet (older 319s) ALD (DRY) > ALD (WET).

(That would mean in a true emergency we should call CFR to hose down the runway?)

Airbus say the numbers are correct. The failure factors for that fleet group, particularly the dry factor, as defined by the various regulatory bodies, are significantly higher than for the other groups and when applied to normal performance data result in the anomaly described above.

Am I missing something here?

[mcdhu]

Try this from Airbus:
The computation of landing distance factors has evolved with the evolution of the retained assumptions, methodologies and tools. These led to have in some cases dry landing distance coefficients inconsistencies between several aircraft models of the same family (for instance A318 landing distance factors have not been computed using the A320' methodology). Consequently Airbus has decided to reconsider and harmonize the method for computing all of the landing distance coefficients. Please note that in the frame of this harmonization the landing distance coefficients, for wet and contaminated runways and for all fly-by-wire aircraft, have been also computed and incorporated (they were already implemented for A340-500 / -600 aircraft).
One criteria among others which have been reviewed for the retained / harmonized method is the analysis of some operational data such as the approach and landing trajectory. In fact the final approach and flare phase trajectory have been "re-computed" in order to replace the previous "perfect theoretical" one (fly over the runway threshold at 50 feet, theoretical and constant approach speed, constant flare altitude / method ...) by an other model which better copes with a "real", more "operational" trajectory. This explains why the harmonization has led to an increase in the dry landing distance coefficient.
Hope that helped!!
Cheers
mcdhu

[Charly]

I have a question concerning this topic:

Actual Landing Distance dry:
50 ft, VREF, dry RWY, Max manual braking, spoilers, no reverse

Required Landing Distance dry:
the above x 1,67

Required landing Distance wet:
Required LD x 1,15

Clear so far....

What is it with the Actual Landing Distance wet (or even contaminated)?
Has it been demonstrated similar to the dry case (Flight testing)?
Or has it been calculated on the basis of ALD dry?
The "search" function didn't help, and a qiuck search on my OMs didn't help either...

Thank you and best Regards

Charly

[Thai997]

While we're on the topic.......

When applying a landing distance factor after a failure of some system, and the runway is wet, do you use the wet or dry landing distance fiigure multiplied by the landing distance factor ??

[Charly]

Hi Thai 997,

you use the actual landing distance wet (all systems operating), and take the wet factor for the failure.

Regards