A320 Fuel Consumption Increase (L/G & Flaps out)

[airbusbatics]

Pertaining to the A320 family.

Let's assume a situation in which you had performed the landing gear gravity extension, (let's say due to hydraulic problem) and possibly with a Slats / Flaps locked situation. For some further freak occurrence you had to Go-Around at your destination and had to proceed to your alternate with the gear down and the slats and / or flaps out (as mentioned in a HYD G + Y SYS LO PR summary for example).

In the manuals it is stated (FCOM 3.02.10 P8) that your fuel consumption will be be penalized by a multiplying factor of 1.6 (Slats extended), 1.8 (Flaps extended) or 2 (Slats and Flaps extended).
Somwhere else in the books it is stated that fuel consumption must be multiplied by 2.8 for flight with gear down.

So my question is... Should I add the 2.8 to the 1.6 (for expl.), should I multiply one by the other or just assume a penalty of 2.8 as my total fuel consumption increase?

Couldn't find any guidelines for this calculation anywhere in the manuals, although they do acknowledge that this situation (flight with gear down and slats / flaps out) is possible...

Any light shed, as usual, would be much appreciated.

[qualitycontrol]

I believe the 2.8 refers to flight with gear down after manual extension i.e. you have the doors dangling. Think Slats+Flaps+Gear with no doors is approx 2 times normal fuel flow.

Hope this helps.

[A4]

You'd have to be having a very bad day to find yourself in this position! If ever you find yourself in the situation where the gear will not come up once you've lowered it make sure the runway is YOURS before you lower it i.e. it's sterile. That means ATC should not allow anyone else to T/O or Land on that runway, so even if you go around you still have a strip to come back to. Of course if you went around due to "nothing seen" then the question has to be asked as to why you were commiting to a questionable field in the first place.

If you do find yourself having to divert then Total Fuel Flow in Kgs/Hr divided into Fuel on Board should enhance situational awareness no end! Alternate runway centre fix as the "to waypoint", ETA on F-PLN/ND, F/Flow x minutes = fuel required...... will you/wont you? Simplisitic I admit, but that's how I'd play it if I ended up in such a dire situation - and I'd make sure the ALT was sterile long before I arrived as well.

A4

[gearpins]

Do remember the fuel flow indicated is a function of current alt,ISA conditions,and a few more factors thrown in. To try and climb a modern airliner in a dirty state (flaps,gears and geardoors to boot-out) is gonna burn fuel at a rate faster than a computer can calculate !!!!

careful choice of airport in terms of Wx, r/w, appr aid etc in the first place should reduce the risk of a GA. demanding a sterile R/W should tilt the odds further in favour thus reducing the reason for GA.If you still have to then I would shoot another approach.

[A4]

Hello Gearpins,

I'm interested in your comments about computers not being able to calculate fuel consumption. If you are refering to FMGC predictions, well they are totally invalid. However, as far as I'm aware the fuel flow indications (EIS2 Airbus) are taken straight from the fuel metering unit which is just upstream from the engines measuring the quantity going into the burners - so surely ALT, TEMP etc are irrelevant because they would also affect the quantity indications in a similar manner. I stand to be corrected however

I'll still apply the basics though:

Quanitity divided by Fuel flow = Endurance

A4

[gearpins]

Hello A4,
I was probably nor too clear in my earlier post.
The primary concern is:
At the time of GA the fuel flow indicated is with referece to the current ALT which is probably a few 1000' Amsl.
Now all through the subsequent climb and cruize the fuel burn would be at a much higher rate.
and the rate of increase is not leniar in that, say the increased f/f at low alt is double the normal, during climb it could be thrice the normal.
IMHO

[A4]

Hmmm. Not sure if we are at cross purposes here. The fuel flow indication is an instantaneous, real time figure - but it should decrease with increasing altitude, and once in the cruise the maths should become slightly easier.

A4

[eight16kreug]

Using the French way of thinking and the Airbus philosophy on ECAM and QRH use, gears down with doors, after a manual extension, would be the most penalizing, thus fuel flow times 2.8 for planning. Penalties are not additive. If they were, the pilot's brain would go into overload, hang or freeze and require a manual computer reset.

[gearpins]

A4,
I agree that in cruise the fuel consumption in cruise would be lesser than at say sealevel. my consern is the climb.

[factsonly]

The point raised about the increased fuel flow is quite valid and the FCOM figures simply highlight the fact that your fuel burn is going to go way up with all that extra drag hanging out. You will do your head in trying to remember how much burns increase in varying failure modes. While I would never say that something like that would not happen in real life, the most obvious place that it will occur is in the sim and the only way to deal with it is to set a power that maintains you close to the manouevring speed for the particular flap/slat configuration. Gear is zero lift drag and simply goes up exponentially with the speed. I would spend a few seconds looking at the fuel flow and the groundspeed (FF/groundspeed =KG/NM) and work out a specific ground range or KG/NM and multiply that by how far I had to go, plus a reasonable manoeuvring allowance. Add your fixed reserve and you will be able to see if fuel is a real issue. Hopefully it won't be but in the simulator scenario, the man who is assessing you will be able to say that the increased fuel burn was considered and either disregarded as not a factor or acted on. It's the real figures (fuel flow/groundspeed) that matter, not the FCOM ones and if you have a reliable method for working out how much fuel you will burn quickly, you will free up a lot of available brainpower for all the other considerations.