Landing Dist Proc for G+Y...How ?

[ikan_terbang]

Hi,
Whilst doing my conversion, I have come to a dead end on this calculation.
Could someone please clarify......and help me out.
HYD G+Y SUMMARY rev 43 PG 1.12, a landing wt of 66 T the given tabulated distance is 2550 m

Now going thro the normal calculation
Landing dist without autobrake dry the value is 910m (qrh 4.03)
Applicable ldg factors are (qrh 2.34)
1. G+Y = 2.8
2. Direct Law = 1.35*
3. Flaps<1 Slat >1, conf 3=1.95* (cannot locate a better combination) I know the Slat will be at posn 3 but there is no table to choose from ??? So maybe I am wrong here !

So the final ldg dist correction will be
1st scenario
910 x 2.8 x 1.95 = 4968m
2nd scenario
910 x 2.8 x 1.35 = 3439m
3rd scenario
910 x 2.8=2548m (pretty close to answer in summary table)

In case 1 & 2 its more than 2550 given in the summary.
can anyone tell me where I am going wrong please.
regards

[Mad (Flt) Scientist]

Uninformed suggestion (I dont know AB)

Maybe the x2.8 factor for the actual "G+Y" case already includes the factors for Direct law and for the config, so you are in effect double accounting (or even triple accounting, if you added them all)

certainly in "our" AFM/QRH when we have a failure case that "causes" others we try not to make you go flicking through the books, but rather roll everything up into the single case.

[dkz]

G+Y is the one you need and will compute the LDG Dist with all the factors associated with it.

[Eric Janson]

ikan_terbang

The factors in the QRH take all the problems associated with the failure into account.

In your example Hyd G+Y the factor in the QRH includes everything associated with this failure.

Landing distance is simply 910m x 2.8 = 2548m. Very close to the 2550m in the summary table.

[Fliegen_Inlander]

How about safety margin?? As prescribed in US -FAA SAFO 06012 ( Aug 31, 2006) to put on 15%, asmin safety margin between ALD and LDA?

[737Jock]

That is not necessary in case of emergency fliegen_inlander. Although in most cases you would do so since rwy length is not an issue

Indeed you only use G+Y landing distance factor as this already includes the factors for direct law and flaps/slats jammed.
You only ever combine single failures and primary failures, not secondary failures.
Also you never multiply multiple factors with a * (ie flaps slats jammed and direct law), you simply pick the highest * factor and use that.

[Fliegen_Inlander]

ah thanks for the answer 737..

[mcdhu]

Guys, just read the instructions on QRH 2.31 and 2.38 and all becomes clear as well as the FCTM.

mcdhu

[ikan_terbang]

After giving this some thought and discussing with sim instructors...........
From QRH 2.38A
Only combine PRIMARY or SINGLE failure....this is the key sentence !!
So if you have a G + Y hyd failure, then the "direct law" additive is NOT considered a PRIMARY failure.

So the calculation of the LDA require @ 66T will be
910 x 2.8=2548m which is pretty close to answer in summary table.

Next query comes to mind. Would I be correct in saying that there are 9 primary failures that require LDG distance calculation from chart 2.32 ans 2.33 QRH.
The primary failure being
1.ELEC
2.SLAT/FLAP
3.FLT CTL
4.HYD
5.A.ICE
6.BRK
7.NAV
8.BLEED
9.ENG

Any comments on my thinking ????
regards

[yoyonow]

Best method is to just follow the ECAM and know what it's telling you.

Primary failures are depicted in a boxed title and have secondary failures associated with them. (An independant failure will not be boxed)

Then, as you say, follow the QRH guidance with regard to combination of failures.

[mcdhu]

Ikan, while I understand your desire to get this completely understood, you are reading too much into all this. As yoyonow says, the Primary Failures are shown by a Boxed Item and the Status Page will say "Landing Procedure Apply".

[rudderrudderrat]

Hi Ikan,

Your Landing Distance only depends on your Ground Speed (depends on VAPP etc.) and the subsequent deceleration using:
Braking (antiskid SYS Green or Yellow / max brake pressure available) & Weight on wheels (loss of spoilers, unusual flaps/slats) and
Reverse Thrust.

[ikan_terbang]

PJ2....
I appreciate your understanding to my queries. Transition from Boeing to Airbus is always a challenge and I will prevail.....but have to ask questions first to clear doubts in my mind!!

Ref 3.02.29 pg 11 REV43
HYD G+Y SYS LO PR

The check list goes as follows
When CONF 3 and VAPP - LG.....GRVTY EXTD
APP SPD ....VREF + 25
LDG DIST PROC.......APPLY
ALT LAW:PROCT LOST
WHEN L/G DN : DIRECT LAW
Fine print....(see DIRECT LAW proc 3.02.27)

Now going to 3.02.27 pg 9 REV37 F/CTL DIRECT LAW
APPR PROC
LDG DIST PROC ......APPLY
refer to QRH part 2 or FCOM 3.02.80

So if I were to follow the AIRBUS FCOM 3 procedure I would need to apply "LDG DIST PROC" twice. That was my original query. The answer will then contradict QRH summary page "Actual landing Dist requirement"
It "seems" to me AIRBUS has omitted the DIRECT LAW landing dist additive requirement in the summary page.

If anyone of you do SIM training, it would be helpful to find out if indeed the ECAM will ask for "LDG DIST PROC..APPLY" when the gear is gravity extended and DIRECT LAW is encountered?

thanks.

[rudderrudderrat]

Hi Ikan,

Yes - I'm afraid the sim ECAM says the same and crews are still tempted to apply an additional factor for Direct Law, by following ECAM "logic."

However it does say in FCOM 3.2.80. Use of the (Landing Distance) Tables "Only combine PRIMARY or SINGLE failures."

But later it confuses some by saying "Multiply the applicable LDG DIST factors together, unless all values are marked with an asterisk (*). If all values are marked with an asterisk, use the highest LDG DIST factor. Multiply it by the additional factor, if any (Refer to QRH 2.31)." and QRH 2.31 says "Direct Law = 1.35* "

So I fully understand how your confusion arises from data presented in this way.

However the Loss of 2 Hyds Check List knows you'll be in direct Law when the gear is lowered and the Landing Distance Factor has taken account of this. My logic in post #12 was that all the factors that can affect Landing distance are mentioned in that QRH procedure. You have already applied Vref + 25, so the Direct Law request for Vref + 10 is already covered.