A320 diverting with ldg stuck down.

[Mooneyboy]

Hello all.

If you had to divert with gear stuck down and wanted to consume as little fuel as possible ( let's say FL100) what speed and config would you divert in? I see there is a section in the FCOM for flight with ldg gear down and there is one table at 230kts clean and one holding table suggesting S speed in config 1. The holding table has slightly less fuel burn than the cruise one but obviously your back at S speed so will take a bit longer.

Also in the QRH fuel penalty factors it suggests 180% ( with gear stuck down) extra burn on top of your normal burn. Why is this penalty so much more than say if you compare holding green dot a/c totally clean to holding with flt with gear stuck down e.g totally clean 60t FL100 2118kg per hour for both engines Vs gear stuck down at s speed 3156kg per hour both engines.

Any help or guidance would be great.

[VinRouge]

our type 150 extra drag counts with the gear down. Its Draggy.

in terms of speeds, have a think of the drag curve vs ias without gear.. add alll that parasitic drag and both your Vimd and LRC speed are both going to go up as the tangent of and the inflexion point of that curve will move to the right. by how much will depend upon how draggy the gear is.

i know its hard to believe but 180% definately sounds about right and why we dont put it down till 4 nm to be more fuel efficient.

[Roj approved]

G’day Mooneyboy,

With gear down, you are almost tripling (x3) your fuel burn, there is lots of drag with the LG and the doors hanging out.

So you do the Fuel penalty, then add it to the planned burn, or as the QRH says,
TRIP FUEL PENALTY = (FOB - EFOB at DEST) x FPF

So, if we just do the numbers for holding, from your figure :

Clean @ 60t @FL100 = 2118kg/h +
Fuel penalty factor (2118*180%) = 3812kg/h
Total fuel req’d to hold for 1 hour = 5930kg

I’m guessing you got some holding Config 1 figures somewhere, my manuals don’t have them, but my guess is Config 1 gives a better fuel flow because of Slats out.

Holding with Slats is ok, but it is pretty slow, and not a great idea in If ICE might be present, but you need to avoid ICE with the gear down too. Also, with all that drag from the gear, Green dot +20kts will be much more comfortable while you sort out the issues.

This abnormal kind of makes things a bit time critical, and with this in mind, better to keep things as simple as possible. Of course, if you have to go to a take off alternate, those sort of fuel flows might be a big problem.

I hope that helps.

If your lucky, Villas will see this, he seems to be pretty clever about all things Airbus, so maybe we can all learn some more.

[pineteam]

Talking for the A320 family: The fuel penalty factors in the QRH are conservative. It's important that your flight plan is properly sequenced to get an accurate consumption estimation.
If you have gears stuck, it would be certainly after airbone or during approach so most probably you won't go anywhere else unless it's one of those days and you took off below landing minima.
In that case, personally I would not use the QRH fuel penalty table. It's faster and more accurate to look at the fuel flow with gears down at green dot speed than trying to sequence your flight plan and make some potentially ''confusing'' calculations at low altitude. Since you would probably not fly faster than green dot unless you want to burn more fuel, whatever is displayed on the fuel flow is a good estimation of how much time you have.
on the A 320, with gears down at green dot speed, it will be roughly 4000kg/h fuel burnt. That's what I observed during my last sim. In a glitch of an eye you have a good idea of your endurance.

[Mooneyboy]

Thank you for your responses. The situation I'm thinking of is flying into short runway having had blue elec hydr pump fail. You elect to continue as ldg dist not increased by much but the on gear extension you lose green system. Gear stuck down. You recover blue system by using RAT but ldg dist now increased a bit more due to 140kts to keep the RAT going. You then have dilemma of short runway with very tight figures or divert to somewhere with long runway 30mins away fuel depending.

Very good point about leaving slats out in icing conditions certainly one to watch. I can certainly see the logic in flying slower with slat out. The ref is FCOM procedures/norm procedures/ supplementary procedures/ l/g flight with ldg gear down.

Looking in the QRH fuel penalty section I think first line it says these are conservative penalty factors. I always understood as mention to essentially your trip X 2.8 but looking at the tables I mentioned is this figure too conservative?

Pineteam, your are quite right. Best to see what your actual burn rate is doing with the gear down at that moment. The fuel flow not prediction should be accurate. So for a diversion 30mins away a very ball park figure would suggest 2tons to get there. You would want at least a ton when you get to your alternate so really at least 3 tons in the tanks before diverting.

[Fursty Ferret]

Somewhere in the FCOM it recommends holding at S speed with gear down. For a diversion it’s more complicated but I’d be going either S speed or green dot. There’s some useful info in the supplementary procedure on flight with gear down.

Edit: vague recollection that QRH non normal fuel flow assumes the gear doors are also dangling in the wind.

[Roj approved]

Thanks MoneyBoy,

Gear down ferries, that’s something the management pilots can do I think 😂

It’s an interesting procedure, and has got some good though provoking stuff in it for when you are having a bad day and the gear won’t come up and it’s below minima to return, if it’s a G Hyd failure, then there’s going to be a bit going on.

Pineteam makes a good point, fly what you are getting fuel flow wise👍

[Roj approved]

Just tried it in the sim at 62T, 3000ft clean with the gear down, fuel flow at green dot was 1900kg/hr a side, so 3800kg/hr.

That’s a lot less than the QRH fuel penalty figures, But it’ll still chew up your flight fuel pretty quick :-)

[Escape Path]

Keep in mind terrain clearance too. If one engine quits, it will obviously affect cruise performance. Last time I had a look at it, just for fun, I think I saw the aircraft won't climb any higher than low to mid-10's. Something to be mindful of if you, like me, happen to fly across big mountain ranges

[Mooneyboy]

Thanks for the replies.

I think if I was given a ldg down ferry I would certainly take a while to sit down and digest potential pit falls. One is you'll go straight to direct law if a degradation in flight laws occurs.

I think as mentioned best just to look at current fuel flow. At roughly 3.8t/per hour total I think a diversion from destination would be a slightly pulse raising experience unless you were flush with fuel.

[vilas]

The situation I'm thinking of is flying into short runway having had blue elec hydr pump fail. You elect to continue as ldg dist not increased by much but the on gear extension you lose green system. Gear stuck down. You recover blue system by using RAT but ldg dist now increased a bit more due to 140kts to keep the RAT going. You then have dilemma of short runway with very tight figures or divert to somewhere with long runway 30mins away fuel depending. when you consider the normal fuel uplift you won't make it to the destination alternate unless this was tankering sector. So either you are doing gear down ferry or diverting to take off alternate with gear stuck are the only possibilities. Holding speed is like endurance speed is only good for holding but will not give range which you need to divert. For 58T S speed is 182kt. while the cruise speed is 230kts. QRH fuel penalty is required to calculate EFOB. Keeping an eye on FF is good airmanship. Long time ago one A300B4 after a GA due poor visibility diverted with flaps stuck to normal destination alternate. The crew didn't monitor the FF and had to force land in a paddy field as the fuel ran out.