Fuel freezing characteristics for operational procedures

[Fabio Miguez 0]

I am writing a guide on Polar Operations for Skywards Virtual (we emulate Emirates Airlines), and in the topic of fuel freezing, the real Emirates has company policy depending on the type of fuel you use, Jet-A or Jet-A1, due to their different freezing temperatures (already covered here in this forum in a number of messages).

 

What I have been unable to find out is if PMDG has built in functionality for these two types or not. I.e. perhaps changing the fuel freezing temperature in the FMC changes the fuel freeze logic behind the scenes. That would be an interesting way to add such flexibility.

 

Or they've modeled their fuel freeze around Jet A only, which is fine too.

 

But I'm looking for confirmation one way or another, so our guidance can be accurate.

 

Thanks in advance,

 

Fabio Miguez

Sorry for the double message, but I got a "Request failed due to server maintenance or busy" prompt after hitting submit, so posted again thinking the first one hadn't gone through. Please delete both of these posts.

[77west 139]

Fabio, I dont believe that fuel freeze is actually simulated. You get an EICAS message but I don't think it would actually freeze and shut down the engines.

 

But I am not sure so its off to Iqaluit for some cold weather testing.

[Fabio Miguez 0]

Hi Wes,

 

I read here that the MD-11 had fuel freeze simulated, and so the 777 might have it too. If it does, then my question stands.

 

Also, another intriguing behavior that PMDG might have modeled, considering their attention to detail, is the possibility of transferring fuel from the wings to the center tanks, where the surface area in contact with an external surface, such as the skin of the aircraft, is lowered. This is most effective, evidently, to slow the cooling of the fuel, as opposed to reverting it.

 

We have an upcoming group flight from Dubai to Los Angeles. My last flight through this route, which is polar, got the fuel very cold, but not enough to set off the FUEL TEMP LOW caution (-37º C by default in the FMC), and that was a 15h42m flight. We'll see what the weather gods bring this time. And good thing there's a good ENSB scenery, you never know when you're going to have that failure at the worst possible time...

 

Looking forward to some more info.

[77west 139]

Also, another intriguing behavior that PMDG might have modeled, considering their attention to detail, is the possibility of transferring fuel from the wings to the center tanks, where the surface area in contact with an external surface, such as the skin of the aircraft, is lowered. This is most effective, evidently, to slow the cooling of the fuel, as opposed to reverting it.

 

I don't believe this is possible on the real 777, and so not simulated. Only perhaps on the ground via the refuelling control panel. It might interest you to know that the fuel in the wings is actually heated slightly from friction of the air over the wings. This is why one of the fuel-freeze solutions is to speed up slightly! (As well as descend in some cases.)

 

I have cold-soaked the Boeing 777-200LR test plane in Iqaluit all day it is now about -30 degrees on both fuel, cabin and everything else. I will do some tests and let you know!!

[hopskip 253]

I don't believe this is possible on the real 777, and so not simulated. Only perhaps on the ground via the refuelling control panel. It might interest you to know that the fuel in the wings is actually heated slightly from friction of the air over the wings. This is why one of the fuel-freeze solutions is to speed up slightly! (As well as descend in some cases.)

 

I have cold-soaked the Boeing 777-200LR test plane in Iqaluit all day it is now about -30 degrees on both fuel, cabin and everything else. I will do some tests and let you know!!

 

Up high in the FL3xx's temps of -55°C are fairly normal Try dropping that oat to -70°C or less to really test it out.

[77west 139]

Up high in the FL3xx's temps of -55°C are fairly normal Try dropping that oat to -70°C or less to really test it out.

I wanted to do it realistically. We will take off at -30, the fuel can only get colder from there. I wanted to cold soak EVERYTHING to make it as realistic as possible. Even opened all the cabin and cargo doors. Amazing even the recirc fans on or off make a difference as to how fast cabin cools down!

[hopskip 253]

I wanted to do it realistically. We will take off at -30, the fuel can only get colder from there. I wanted to cold soak EVERYTHING to make it as realistic as possible. Even opened all the cabin and cargo doors. Amazing even the recirc fans on or off make a difference as to how fast cabin cools down!

 

Aha, fully cold soaked. As in "Get your arctic survival gear to sit in the cockpit" haha.

[77west 139]

Aha, fully cold soaked. As in "Get your arctic survival gear to sit in the cockpit" haha.

Yeah that's it!! The same testing they do for real! When I start the APU the packs will warm the cabin up fast enough.

[Fabio Miguez 0]

Wes, I'm aware of the friction energy transfer, I actually had to do that in real life once .

 

I wasn't aware it's not possible to transfer fuel from wings to center tank in the 777. My own "type rating" program is still being designed, I'm merging the real training program of two different airlines, and designing the training flight sessions still, so my technical knowledge on this airframe is close to nil at the moment. Thanks for sharing!

[77west 139]

Wes, I'm aware of the friction energy transfer, I actually had to do that in real life once .

 

I wasn't aware it's not possible to transfer fuel from wings to center tank in the 777. My own "type rating" program is still being designed, I'm merging the real training program of two different airlines, and designing the training flight sessions still, so my technical knowledge on this airframe is close to nil at the moment. Thanks for sharing!

I tried to do that once but all you achieve is redirecting fuel to the engines. I think the system logic is to try to keep fuel flowing towards the engines at all times, to transfer fuel to centre tank would require somehow closing the engine valves and opening the centre tank valves without enabling it's pumps. Naturally this would stop the flow of fuel to the engines. The only way to do this is via the refuelling panel on the ground, I bet that there is system logic to prevent any fuel transfers while the engine fuel valves are open.

 

Anyhow, I believe the fuel might be better off in the wings where friction can heat it slightly.

[Fabio Miguez 0]

Hey Wes, just checking in to see if you got any results from your tests...?

 

Thanks!

[77west 139]

Hey Wes, just checking in to see if you got any results from your tests...?

 

Thanks!

Hi Fabio

 

I have not yet had a chance to try it but today is a holiday here in NZ so should be able to soon!

[77west 139]

Hey Wes, just checking in to see if you got any results from your tests...?

 

Thanks!

Sadly after testing, my conclusion is that it is not modelled. I get FUEL TEMP LOW at -35C and at -47C the fuel temp indicator goes orange. Left it all the way to -52 and nothing happened yet...