Julesmusician From , joined Dec 1969, posts, RR: Posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 5651 times:
Question:
Today over Europe and the USA temperatures are showing as low as -58C predicted flight levels 300 and above. Since Jet A1 Fuel starts freezing from -47c downwards and Jet A fuel (as served in the US) freezes from -40c downwards - well, what happens? Surely airliners all over the place will be showing freezing fuel warnings and not be able to be above that flight level causing chaos?
Mjzair From United States of America, joined Nov 1999, 386 posts, RR: 1 Reply 1, posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 5649 times:
Remember, that these temperatures are not outside the norm. The ISA temp at 360 and above is -56 so, what you have there is not all that different than ISA.
Fuel is warmed by engine oil passing thru the fuel tanks, and at the same time, the oil is cooled by the fuel. This helps keep the temp of the fuel warm.
Hope this helps.
Mark
Julesmusician From , joined Dec 1969, posts, RR: Reply 2, posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 5648 times:
Then if engine oil is warming fuel this must make fuel temperature warnings for pilots redundant as the oil will always be hot enough to warm the fuel ot a reasonable level?
Mjzair From United States of America, joined Nov 1999, 386 posts, RR: 1 Reply 3, posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 5642 times:
I beleive you are correct, as far as I am aware, the aircraft that I fly does not have a over temp warning for fuel - as a matter of fact, the only limitation that I know of says that the bulk fuel temp (in the tanks) must be above a certain temp (I think it is -5), and there is also a minimum in line temp, but I cannot recall what these are, but once again, there is no specific warning for this as you must call up the Fuel Synoptic page. I believe that there is no warning as different fuels that can be used in the aircraft have different temperature limits.
3201 From , joined Dec 1969, posts, RR: Reply 5, posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 5637 times:
Fuel freezing is an issue on polar routes -- see, for example, this article. There are definitely not only on-board systems to detect, but also offline tools to predict fuel-freezing risk, based on amount of time spent at each temperature (thus sensitive to route, altitude, time of departure, airspeed, etc.) so that operations can be planned to avoid serious fuel-freezing problems.
That said, yes, -58C is normal, I'd actually have guessed they're normally quite a bit colder this time of year. Northwest of Norway today I'm seeing temps in the -75 range, for example, but most of the rest of the northern hemisphere is -60 or warmer, with -56.5 standard (so -58 only 1.5 deg colder than a "standard" day).
Fr8Mech From United States of America, joined Sep 2005, 3059 posts, RR: 7 Reply 6, posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 5629 times:
Quoting 3201 (Reply 5): There are definitely not only on-board systems to detect
Fuel filter differential switches are commonly called an icing indication system. In fact, as I recall, the classic B747 has an icing light which is connected to this switch. When the light illuminates, the flight engineer turns on the fuel heater. On the JT9 this is a air/fuel heat exchanger which uses 13th (?) stage air for heating. I believe the limit is 1 minute on. This system is supplemental to the fuel/oil heat exchanger.
While fuel does freeze at temps higher that than the operating temps at altitude, we need to remember our science. The large amount of fuel in tanks will take a substantial amount of time to reach freezing temperature.
Also, the hydraulic coolers in some aircraft help keep fuel warm. The engine fuel/oil heatexchangers also do a good job of keeping the fuel going to the engine warm. The boost pumps in the tank certainly generate enough localized heat to keep the fuel around the feedbox warm.
When seconds count...the authorities are minutes away!
Julesmusician From , joined Dec 1969, posts, RR: Reply 7, posted (6 years 4 months 4 weeks 1 day 13 hours ago) and read 5623 times:
Interesting, thanks for the answers. It is interesting that the US appears to use a fuel of different freezing temperature than Europe, according to the information I can find....
DALMD88 From United States of America, joined Jul 2000, 2249 posts, RR: 15 Reply 8, posted (6 years 4 months 4 weeks 1 day 12 hours ago) and read 5610 times:
I've never seen engine oil routed through the fuel tanks. Many large aircraft route Hydraulics throught the tanks to cool the hydraulic fluid. These heat exchangers are usually only in one or two tanks, not all. The fuel does usually go through a Fuel-Oil heat exchanger just before it goes into the fuel control. This is on the engine and not in the tanks. The main purpose is to melt any water ice that may be present in the fuel.
So why doesn't the fuel freeze? Think of the tank as a pond. When the temp dips down to 20F does the pond freeze overnight? Not usually, there is to much heat energy still in it. The time below the freezing point is too short to cool that volume of water. The same is true in the airplane. The outside temp may be below the freezing point but the fuel itself still hasn't cooled to air temp.
CosmicCruiser From United States of America, joined Feb 2005, 2045 posts, RR: 18 Reply 9, posted (6 years 4 months 4 weeks 1 day 10 hours ago) and read 5581 times:
Just a quick reply to the question. The fuel being heated prior to the eng. is not the real question. As the fuel approaches the freeze point in the tank it can become "a slushy'. In the MD-11, for example, as the fuel nears the freeze point recirculation begins that moves the fuel around in the attempt to move it to a warmer place. EG. the tail fuel is moved forward to and then replaced with fuel from another tank. If the recirculation doesn't raise the temp to a given value then a "fuel temp low" alert is displayed and a lower altitude may be necessary. I've never seen it really be a problem but some 12 hr. flts have gotten close.
Matt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 5 Reply 10, posted (6 years 4 months 4 weeks 1 day 10 hours ago) and read 5574 times:
Quoting Mjzair (Reply 1): Fuel is warmed by engine oil passing thru the fuel tanks, and at the same time, the oil is cooled by the fuel. This helps keep the temp of the fuel warm.
Quoting DALMD88 (Reply 8): I've never seen engine oil routed through the fuel tanks. Many large aircraft route Hydraulics throught the tanks to cool the hydraulic fluid.
Kaddyuk From Wallis and Futuna, joined Nov 2001, 4125 posts, RR: 33 Reply 11, posted (6 years 4 months 4 weeks 1 day 10 hours ago) and read 5567 times:
The B744 has tubes that pass through the wing tanks as these are the main source of fuel and should always be filled first. Hydraulic fluid passes through these pipes and acts as a cooler for the hydraulic fluid. It does warm the fuel but not by a massive amount. No oil is routed through the wings.
The engine has an Oil/Fuel heat exchanger which has hot oil on one side and cold fuel on the other, the interchanger then cools the oil and heats the fuel to about 20 degrees celcius (IIRC). Which is why if you drain the fuel system soon after shutdown you will find areas of warm fuel.
Most Jet-A1 fuels contain anti-waxing additives (Essentially Anti-Freeze). The slushyness found in fuel is caused by the water freezing in suspension in the fuel itself.
Fuel takes an extremly long time to both warm and cool due to such a large mass involved. I've seen 14 tonnes of fuel only rise 3 or 4 degrees in 9hrs on a cold day. In warmer/colder climates the process is sped up or slow down.
Whoever said "laughter is the best medicine" never had Gonorrhea
ExPratt From United States of America, joined Mar 2000, 311 posts, RR: 0 Reply 13, posted (6 years 4 months 4 weeks 1 day 6 hours ago) and read 5507 times:
The static air temperature is typically -55 to -58 degrees. However, the ram air temperature is usually 20 degrees warmer. So there is not a real concern fo most operations for fuel freezing, which is not really freezing but the paraffin chains coming out of solution. There is a concern on U.S. departing polar flights. Jet A-1 pumped at non-U.S. stations has the lower freeze point and eliminates the problem of fuel freezing. Virtually all jet fuel pumped in the U.S. is Jet A that has a slightly higher freeze point. For polar flights, the freeze point of the fuel being loaded into a polar route flight is measured plane side. The freeze point info is provided to the crew and if the ram air temperature gets within 2 degrees of the freeze point, the crew has to take some action, either accelerate the airplane to increase the ram air temp or descend.
CosmicCruiser From United States of America, joined Feb 2005, 2045 posts, RR: 18 Reply 14, posted (6 years 4 months 4 weeks 1 day 5 hours ago) and read 5498 times:
Quoting ExPratt (Reply 13): Jet A-1 pumped at non-U.S. stations has the lower freeze point and eliminates the problem of fuel freezing.
As I said in my post above regarding the fuel freeze point, my only flight to see fuel recirculation was on a CDG-SFS(Subic Bay)(12hr) in the winter and the jet was fueled with Jet A-1 (-47deg).
ExPratt From United States of America, joined Mar 2000, 311 posts, RR: 0 Reply 15, posted (6 years 4 months 4 weeks 1 day 3 hours ago) and read 5475 times:
Quoting CosmicCruiser (Reply 14): As I said in my post above regarding the fuel freeze point, my only flight to see fuel recirculation was on a CDG-SFS(Subic Bay)(12hr) in the winter and the jet was fueled with Jet A-1 (-47deg).
Is the fuel recirculation a direct crew action or does the MD-11 automatically do it when the fuel temperature gets that low?
Pilotpip From United States of America, joined Sep 2003, 3015 posts, RR: 13 Reply 16, posted (6 years 4 months 4 weeks 1 day 3 hours ago) and read 5470 times:
It also takes a very long time for the fuel to cool when you have a quantity that large stored. As Cosmic stated, he was only starting to be concerned after a 12 hour flight. A couple hours at cruise isn't going to cause much concern unless the fuel is damn cold in the first place.
HAWK21M From India, joined Jan 2001, 30162 posts, RR: 61 Reply 17, posted (6 years 4 months 4 weeks 1 day 2 hours ago) and read 5456 times:
On the B737s Fuel Heaters are Provided.Also FCOC or Fuel Cooled oil coolers help indirectly warm Fuel.Apart from the Hydraulic System Heat Exchangers in the Wing Tanks.
regds
MEL
CosmicCruiser From United States of America, joined Feb 2005, 2045 posts, RR: 18 Reply 18, posted (6 years 4 months 4 weeks 17 hours ago) and read 5419 times:
Quoting ExPratt (Reply 15): Is the fuel recirculation a direct crew action or does the MD-11 automatically do it when the fuel temperature gets that low?
Hello ExPratt, it's automatic; the crew has no control. When the fuel temp reaches 6 deg.of the FP in tank 3 the fuel is circulated between 1 & 3 until the temp rises 5 deg or for 15min. If the fuel doesn't make the 5 deg rise you get the "Fuel Temp Low' alert. In the tail, the circulation begins 8 deg from FP. If it gets within 5 deg of the FP 1/3 is sent forward to mix with warmer fuel then sent back. If it gets within 3 deg of the FP tail fuel mgt. is terminated and all tail fuel is sent forward. The important point is for the crew to enter the correct fuel type into the FMS.
Quoting Pihero (Reply 9): Six years ago, passing the Turkey -Bulgaria boundary :-84°c.
I quickly realised why aircraft ahead of me were calling for fast descents, as they had been some 10 hours cold soaking their fuel tanks, coming from the East. I guess fuel temp was for them a lot more critical than for me, originating from Damascus.
I still got a "Fuel low temp" warning and did what everybody else did, i.e. get the hell out of that cold bubble by descending from FL 350 to FL 220.
The B744 has tubes that pass through the wing tanks as these are the main source of fuel and should always be filled first. Hydraulic fluid passes through these pipes and acts as a cooler for the hydraulic fluid
thats what i meant, i was saying in response to the last part of the second quote i gave! sorry if that confused you!
ExPratt From United States of America, joined Mar 2000, 311 posts, RR: 0 Reply 21, posted (6 years 4 months 4 weeks 13 hours ago) and read 5352 times:
Quoting CosmicCruiser (Reply 18): The important point is for the crew to enter the correct fuel type into the FMS.
You answered my next question, how does the airplane know what the freeze point of the fuel. Are you limited to A and A-1, or do you also have other choices?
CosmicCruiser From United States of America, joined Feb 2005, 2045 posts, RR: 18 Reply 22, posted (6 years 4 months 4 weeks 10 hours ago) and read 5321 times:
Quoting ExPratt (Reply 21): Are you limited to A and A-1, or do you also have other choices?
You have other choices and even if the type isn't there you can enter the freeze point manually in the init page so your covered.
ExPratt From United States of America, joined Mar 2000, 311 posts, RR: 0 Reply 23, posted (6 years 4 months 4 weeks 4 hours ago) and read 5267 times:
Quoting ExPratt (Reply 21): You have other choices and even if the type isn't there you can enter the freeze point manually in the init page so your covered.
What are your other choices? Jet B, JP-4, JP-5, JP-8. If you enter a freeze point into the FMC, do you use a number from a test that was accomplished or the spec limit for that type of jet fuel?
On those occasions that you enter a specific number for freeze point, do you also have to enter a number for specific gravity and/or density?
CX flyboy From Hong Kong, joined Dec 1999, 6129 posts, RR: 57 Reply 24, posted (6 years 4 months 4 weeks 3 hours ago) and read 5262 times:
On the 777 at normal cruise speeds and altitudes we have a ram air rise of about 31 degrees. If our fuel is reaching freezing point we have a few options. Either speeding up to increase the ram air temerature rise, descending, or rerouting to find warmer air. In reality we rarely see the need for any of these as the fuel does take a while to cool down, but on the 744 flying long haul I have descended before, and flown faster before in a bid to increase fuel temperature.
CosmicCruiser From United States of America, joined Feb 2005, 2045 posts, RR: 18 Reply 25, posted (6 years 4 months 4 weeks 3 hours ago) and read 5261 times:
Sponsor Message: 
From , joined Dec 1969, posts, 
From United States of America, joined Nov 1999, 386 posts, 
From Wallis and Futuna, joined Nov 2001, 4125 posts, 
From Sweden, joined Nov 2005, 3489 posts, 
From India, joined Jan 2001, 30162 posts, 
From Mongolia, joined May 2004, 2736 posts, 
From Hong Kong, joined Dec 1999, 6129 posts, 
Sponsor Message: 
Printer friendly format
