A320 Landing Dist. Dual HYD vs Emer Elec

[peacekeeper]

Hi Guys,

Can anyone point out if I'm missing something stupid. I can't really see why the landing distance would be longer for emergency electrical configuration than for a G+Y hydraulic failure. It seems on the face of it that in EEC you benefit from having a spoiler extra and flaps.

Also, if you were unfortunate enough to have a Dual Eng failure, which landing distance procedure is most appropriate since there isn't one specifically? If you have the privilege of a runway, it would be nice to know if you'll stop at some point on it.

I think I've looked at the books too much, it's all moulding into 1 now!

Thanks in advance.

PK

[Groundloop]

As far as I can see the multiplying factor for an EEC is 1.7 and for a G+Y failure it is 2.1 - or is my FCOM way out of date!

[Natstrackalpha]

In EEC do you have Auto brake? Do you have reversers? Do you have flaps? Do you have antiskid? Do you have nose wheel steering?

[peacekeeper]

As far as I can see:

EEC - No reverse
Only Spoilers 1,2,5
(Flaps yes off SFCC 1)
No anti skid
Alternate Brakes
No NWS

G+Y Failure - No reverse
Only spoiler 3
No Flaps
No anti skid
Accu only braking

So I can't see why EEC should require greater landing distance.

[peacekeeper]

The factors from my QRH based on dry figures are:

EEC - 3.25
G+Y Failure - 2.75

I should also correct my title, these are A319 Figures (Sorry)

[Cough]

Not forgetting that some aircraft have a min RAT speed of 140kt during EEC which is going to extend the LDR...

In EEC do the engines drop from flight idle to ground idle on touchdown? Can't remember...

Peacekeeper..

For a dual eng fail, I wouldn't worry about the runway length. Look at the options and decide quite quickly whats going to fit the bill. Put it this way, say you spend 3 minutes of rattling around the QRH factoring in this and that you aren't going to have enough height to decide which airfield to pick anyway (particularly the ROD at high altitude is massive as you chase the 280kt relight speed). Secondly, performance is only relevant if the speed across the threshold is correct, with a touchdown at the correct point, neither points are a given in the dual eng fail case. Thirdly, you may touchdown with an APU operating (subject to aircraft fit - In some, it is not recommended to attempt a start) and if you have the APU operating with the yellow pump you may just have normal brakes.....

[Natstrackalpha]

So I can't see why EEC should require greater landing distance.

Maybe its something to do with No Reversers and no Anti-Skid
Maybe if you don`t have reversers they think you may need more runway - maybe if you do not have anti-skid on ice or water then you skid and need more runway, in order to stop the aircraft before it toddles off the end of the runway perhaps . . ?

[peacekeeper]

Indeed! And in keeping with the original question, I was refering to why EEC requires more landing distance than Dual HYD G+Y failure which appears to have less stopping capability and no flaps.

Thanks Cough for the thoughts on Dual Eng failure, I absolutely see your point, the main reason I wondered about this was because the FCOM procedure refers you to the landing distance Procedure in the Status message.

Cheers

[rudderrudderrat]

Hi peacekeeper,
It seems on the face of it that in EEC you benefit from having a spoiler extra and flaps.
I agree. We asked AI the same question because it doesn't make sense to my logic. AI answered saying something like:
with no flaps - there is more weight on the wheels when the nose wheel is down, therefore more grip on the tyres, therefore more effective braking. (I agree with that logic).

However - in both cases we are restricting the brake pressure to 1,000 psi due no anti skid to prevent the tyres from skidding - so why would that make any difference? It must be the same retardation force in both cases, so landing distance must depend on the VApp. It still doesn't make sense to me.

[Aikon]

This is very simply because of the fact that your Vapp in (G+Y Hyd inop) is higher than the Vapp in (Elec Emergency). If I remember correctly, your delta Vref for (G+Y) is 25kts whereas delta Vref for (Elec Emergency) is only 10kts.

[Fursty Ferret]

Aikon - which is why we're pondering the reason that the landing distance is greater in EEC than the dual hydraulic failure.

[Aikon]

In G+Y Hyd inop, essentially you do not have flaps hence the higher speed. In elec emergency, you have both slats & flaps.

[Dani]

EEC - 3.25
G+Y Failure - 2.75

I don't have a 319's QRH, but I think your 3.25 factor highly unlikely. On a 320 it's 2.65 for EEC and 2.8 for G+Y. Maybe these are special company limits?

Dani

[I-2021]

Hi Dani,

I don't have a 319's QRH, but I think your 3.25 factor highly unlikely. On a 320 it's 2.65 for EEC and 2.8 for G+Y. Maybe these are special company limits?

Dani

On my QRH I've got 3.15 for EEC Dry and 2.80 for G+Y Dry. Are you sure about your EEC factor ?

I agree. We asked AI the same question because it doesn't make sense to my logic. AI answered saying something like:
with no flaps - there is more weight on the wheels when the nose wheel is down, therefore more grip on the tyres, therefore more effective braking. (I agree with that logic).

Hi rudder,

sounds quite logical to me as well. Can't see any other clear direct reason but I'll try to investigate too. :ok:

[peacekeeper]

There could always be a mistake in my QRH but the Landing distance factor for EEC on DRY runway 3.25 and Dual HYD G+Y is 2.75. I have heard a similar explanation regarding another QRH anomaly which also seemed to do with Braking efficiency with less flaps.

In the DC Emer Config the factor for flaps full is greater than flaps 3 which seems to go against all logic, but never the less could be true. Even though the QRH recommends taking flap full, it will result in a higher landing distance, WEIRD!

[Natstrackalpha]

Indeed! And in keeping with the original question, I was refering to why EEC requires more landing distance than Dual HYD G+Y failure which appears to have less stopping capability and no flaps. -

Yep, apologies-saw it later . . . :ugh:

[Cough]

Just a thought.

Say you didn't have a G+Y failure, but flaps locked with no anti skid. Whats the landing distance factor then?:E