Fuel Heater

[TC1 0]

Are the fuel heaters model in the 747? In the manual it states a problem could/would/should occur if the temp of the fuel reached a -37. Is there a switch model to turn on/off the fuel heaters? I was unable to locate the switch.ThanksTom

[Samwise 1]

There are no fuel heaters on the 747-400. A quick search on google extracted the following information from the Internation Aviation Safety Association website:

When fuel temperature decreases to 3°C above the freezing point, a message of FUEL TEMP LOW displays in the 747-400 and 777 flight decks; the message FUEL TEMP LO is displayed in the MD-11 flight deck. If this condition is reached, the flight crew must take action, as described below, to increase the TAT to avoid further fuel cooling. In consultation with airline dispatch and air traffic control, the flight crew decides on a plan of action. If possible, the action should include changing the flight plan to where warmer air can be expected. Another action is to descend to a lower altitude. The required descent would be within 3,000 to 5,000 ft of optimum altitude. In more severe cases, a descent to 25,000 ft might be required. Recent experience on polar routes has shown that the temperature may be higher at higher altitudes, in which case a climb may be warranted. The flight crew also may increase airplane speed; an increase of 0.01 Mach results in a TAT increase of 0.5° to 0.7°C. (It should be noted that any of these techniques increases fuel consumption, possibly to the point at which refueling becomes necessary.) It takes approximately 15 min to 1 hr for a change in TAT to affect the fuel temperature. The rate of cooling of the fuel is approximately 3°C/h. A maximum of 12°C/h is possible under the most extreme cold conditions. A minimum in-flight fuel temperature advisory message provides a margin of safety under all atmospheric and operational conditions to ensure that the fuel will continue to flow to the boost pump inlets. Besides the 3°C margin between the advisory message temperature and fuel freezing point, there typically is a 6°C difference between the freezing point and pour point of fuels, which provides an additional margin. A review of the service history of transport airplane operations worldwide for the past 40 years does not show a single reported incident of restricted fuel flow because of low fuel tank temperatures. This service history affirms that the criteria used to establish the advisory message are adequate and conservative. However, flight crews on polar routes must be knowledgeable about fuel freezing points. Flight crews also must be cognizant of the en route fuel temperature and the possible need for corrective action to ensure continued safe, routine polar operations.

[TC1 0]

Thank you. What triggered my question was today I was undertaking a flight from KJFK to HECA and somewhere over the North Atlantic I notice that the tempeture of the fuel was a -31. One of the other models that I fly, the 727-100/200 has fuel heaters and was interested in what the 747 does, since it is capiable of flying at a higher altitude and in a much colder environment.Tom

[jon b 2,058]

The classic 747 had fuel heaters I believe, the 400 just has a heat exchanger where the hydraulic system dumps some heat into the fuel system.European(and some other regions) fuel has a lower freezing point of -47c and so if you have refuelled 3 times using only the european stuff your minimum fuel temp is -44c and the eicas low fuel temp can be ignored.We have a mixing chart if we landed in the uk with say 10 T of american gas on then refuel with the european gas up to 90T we can derive from the chart a suitable freeze point.I've had low fuel temps a couple of times on the NATs, the latest was only a couple of weeks ago where the OAT was about 4 degrees lower than forecast at -69c. I got the speed up to M.88 to try and keep the temp up but it still kept falling so had to descend 4,000 ft to get to "warmer" air. Lucky on that occasion the track wasnt busy so we could get a lower lever, last year I had to call a pan and offset from the track before descending as they didnt have any lower levels , which is a real pain.Normally anything over 2 hours flying in -65 or below will start to give you problems.cheersJon Bunting

[por930 51]

Hi Jon, I can imagine winter flights on say the YSSY-SAEZ run,(will travel this route April) not too much traffic and lower level diversion pretty straight forward, but over Europe could be a bit challenging.Tell me, when the low fuel temp warning flags, would you immediately check your fuel mix/temp chart to find what your operating temp is with the fuel mix you have, to determine if you can ignore the message? or look for warmer altitude straight away?When you declare a PAN, are questions asked back home from head office?

[jon b 2,058]

Hi Geoff,If you spot the fuel temp getting low first thing to do is consider what sort of fuel you have onboard. If you are out of the US you know straight away you have -40 fuel,if youve refuelled in europe after coming from the US you can refer to the chart, if you have refuelled 3 times with -47 fuel you can consider any residual -40 has been purged.You'd work out your fuel freeze point first as you dont want to be speeding up or descending unless you really have to.The PAN call was to the oceanic controller just to give a bit of weight and urgency to the scenario, may or may not be required, on this occasion things weren't happening as quick as would have liked. I also just did a general broadcast to nearby traffic on the tracks so they know what you as doing as you move off the tracks.No, no questions are asked from home base, its just normal low key stuff really.cheersJon

[TC1 0]

Hey Jon, thanks for such an excellant answer.Tom

[Andrea1 6]

Hi to all,Generally all turbofans i.e. GE CF6-80 etc have got fuel heaters by heat exchanger between engine oil (NOT HYDRAULIC FLUID) and fuel (oil cools down, fuel heat up) here's one of the reason for which oil temp is higher during ground operation and idling then in flight and at high power settings... (when on ground on idle there's few fuel into the manifold to cold down the oil).Best RegardsAndrea Buono

[jon b 2,058]

Hi to all,Generally all turbofans i.e. GE CF6-80 etc have got fuel heaters by heat exchanger between engine oil (NOT HYDRAULIC FLUID) and fuel (oil cools down, fuel heat up) here's one of the reason for which oil temp is higher during ground operation and idling then in flight and at high power settings... (when on ground on idle there's few fuel into the manifold to cold down the oil).Best RegardsAndrea Buono

Quite right, the 744 also has heat exchanges in the main tanks which are for dumping the heat from the hydraulics rather than heating the fuel, but every little helps .cheersJon Bunting