Jet A1 Question

[MightyGem]

British military helicopters and some civilian types, require some sort of icing inhibitor (FSII or prist)in the fuel for operating where the fuel temperature falls below about +5degC.. .. .As most airports (in Uk/Europe) use Jet A1 which doesn't have any anti ice, what do the operators of big jets do? Do they have a requirement for anti ice? If not, why don't they need it?. . <img border="0" title="" alt="[Confused]" src="confused.gif" />

[Pegasus77]

Jet A(1) freezes when temperature becomes below minus 40-43 deg Celcius.... no need to use any icepreventing extra's.. .Only on long haul flights (long time at a high and cold altitude) your fuel temperature is something to think about (i.e. fly lower in the end, so your fuel doesn't freeze).. .. .I reckon these helicopters you mention don not use JetA??

[MightyGem]

I'm happy about the freezing point of the fuel, but the reason we need the anti ice, is for the prevention of ice crystals from any water present blocking lines and filters.. .. .Yes, we use Jet A and add anti ice as required.. . . . <small>[ 17 March 2002, 12:36: Message edited by: MightyGem ]</small>

[JazzyKex]

Most big jets use a system of heat exchange cooling the hot engine oil by passing it through the fuel tanks and using this heat exchange to heat the fuel prior to it being supplied to the engines. It provides enough heat to negate the need for anti ice in the fuel to avoid fuel line blockages but as Pegasus says you still need to keep an eye on the overall fuel temp. Another thing to think about is to avoid landing with too much fuel in wing tanks when you have a quick turnaround to avoid ice build up on the top sufaces of the wings when on the ground.

[Fresca]

I believe Jet-A1 has a freezing point of -47°C and Jet-A of -40°C. The procedure is to never allow the fuel temp to go below 3° above the fuel freeze point. If that happens one must either increse speed, or descend to a lower altitude. Normally this is not a problem as in cruise in the mid 30.000' at Mach 0.8 with OAT around -50 the TAT would be around -30°C. . .. .I have been told that at those temperatures (freeze point) the fuel does not actually freeze but the wax parrafins that are in the fuel would turn into solids and can block the fuel pumps.. .. .I have only once seen the fuel temp get close to the prescribed limits, and that was after a 6 hour flight over northern Canda and Greenland.

[MightyGem]

Jazzy, I think that probably answers my question. Thanks