A320 Landing Distance Procedure - Multiple Failures

[captainpaddy]

Just started the A320 groundschool and I have what is surely a silly question:

As an example if you have a G & B Hydraulic failure, the landing distance procedure in the QRH says to increase your landing distance by 1.6. Other systems which are affected by the hydraulic loss include loss of autobrake, loss of 3 spoilers, slats jammed and we end up in Alternate then Direct Law.

I assume that the landing distance increment of 1.6 accounts for all affected systems or do you follow the procedure for multiple failures and account for everything individually, multiplying their factors?

To sum up, is the procedure for multiple failures only used when the failures are completely unrelated and independent? e.g. G&B Hydraulic loss (factor 1.6) followed by and unrelated but unfortunate loss of anti-skid (factor 1.5) would result in a total factor of 2.4???????

I'm confused again. :{

CP

[ZeeDoktor]

take whichever is higher as the multiplier. in your example, 1.6 it is.

[TopBunk]

In BA our QRH (which I guess is derived from the Airbus QRH) says:

For a single failure
- determine the required ldg conf
- determine the delta Vref
- Vapp = Vref + delta Vref + wind correction
- determine the ldg dist factor

For a multiple failure
- use the lowest ldg conf
- use the highest delta Vref
- mulitply the ldg factors together, except where all failures indicatd by an *. In this case take the highest factor.

Example:
(1)
Flaps Fault (F<3, S>=1) Ldg Conf 3; delta Vref = 10kt; ldg dist x 1.15*
Brk Anti Skid Norm conf; delta Vref = 0; ldg dist x 1.5
Result Ldg Conf 3; delta Vref =10; ldg dist x 1.725

(2)
Altn Law Ldg Conf 3; delta Vref = 10; ldg dist x 1.2*
Flaps Fault (F<1, S>=1) Ldg Conf 3; delta Vref = 25; ldg dist x 1.3*
Result Ldg Conf 3; delta Vref = 25; ldg dist x 1.3

So, in summary, sometimes you multiply the factors sometimes just take the larger, it depends on the nature of the faults.....

HTH

[TopBunk]

capt paddy

just to add, in the example you give, the 'Loss of G+B Hydraulics' correction accounts for all associated system degradations, so the required conf for landing is F3, +25kts and factor of 1.6 for the required ldg distance.

[captainpaddy]

Thanks TopBunk,

I think that's answered my question.So the multiplier procedure only applies when you are dealing with two seperate problems? Like when a second failure occurs that is not as a result of the first?

CP

[TopBunk]

CaptPaddy

That is not quite what I am saying.

If you have a G+B Hyd failure, then the requirements of all the system implications are covered by the single QRH entry.

If you have multiple problems, you MAY have to multiply the corrections or MAY NOT depending on the combination of the failures.

Looking at the (BA) QRH, the failures with an asterisk (*) against them are:

Flt Ctl - Altn/Direct Law, ELAC 1+2, L(R) ELEV, STAB JAM, L+R ELEV
Flaps/Slats - Any failure
NAV - Dual IR Fault, DUAL ADR Fault, NAV 1+2+3 Fault
ENG - Rev Unlocked with buffet

If the combination of failures is limited to the above you take the highest factor for the landing distance, not the multiple.

If however the combination of failures is not limited to a combination of the above you must multiply the factors.

So, as in my previous reply, FLAPS + BRK ANTI SKID => multiply factors as only one is *; and if FLAPS + ALTN LAW => do not multiply as both *.

Clearer?

[captainpaddy]

Yes indeed!

Sorry, I should have said in my previous reply that it wouldn't apply to two or more starred failures. I understand that now. I have been told that it can loosely be taken that starred failures generally apply to landing distance increments as a result of higher approach speeds and non-starred are generally the result of stopping problems. Hence the reason that two non-starred items need to be multiplied (e.g. spoilers & anti-skid) as there effects are compounded in the attempt to stop. If you have two starred items you will be using the highest approach speed indicated and therefore the highest landing distance factor on it's own will cover it's effect. (I realise that this logic may not apply to every combination)

Many thanks for your help. Now I can get on with being confused with some other subject!

Cheers,

CP