Ice on Jet Fan Blades

Old Dec 8, 03, 6:12 pm
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Ice on Jet Fan Blades

I was delayed 1 hour out of EDI today due to ice that built up on the jet fan blades during the inbound descent through freezing fog.

(We then had another 3 hours waiting for a slot due to fog at LHR - but that isn't the point of the post).

If the plane can pick up ice on the fan blades during descent throught freezing fog - obviously they can sort it on the ground. But what happens when we take off through the same freezing fog? Do the fan blades pick up ice - or is it that they spin faster on take off.

It took them 20 miutes to de-ice the engines after the landing - why isn't it a problem on take off?

[This message has been edited by edi-traveller (edited Dec 09, 2003).]
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Old Dec 8, 03, 8:51 pm
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parts of the airplane pick up ice during decent due to the aircraft being cold soaked while flying at high altitude. As the super cold aircraft (-50C) decends through moisture in the air, the moisture sticks to certain parts of the aircraft, like the backside of fan blades. After the aircraft lands it warms up to ground temperature and so this does not happen during accent.
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Old Dec 8, 03, 10:17 pm
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So why isn't ice on the turbine blades a flight problem during the descent?
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Old Dec 9, 03, 12:40 am
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The ice does not form during the decent. The blades are moving too fast with too much centripetal force for ice to form. But, as mention above, the aircraft will be cold soaked due to flight at altitude and if the ground temp is low (EDI in December??) and damp (fog??) then ICE will form on the ground.

The problem in this case was likely that the decent through the freezing fog did not allow the blades to increase in temp as would be normal in warm air conditions. The rapid rotation through warm (not freezing) air will remove the coldness from the blades very quickly. If the air there are rorating in is below freezing, then the aircraft will land with the blades still below freezing temp. Then any moisture in the air on the ground will form ice while the aircraft is on the ground.

This ice must be cleared before the aircraft can be used again. When the ground temp is sufficient, this will happen naturally. Although the aircraft is cold soaked, most of the materials and individual parts are, by design, poor thermal conductors. Even the engine fan blades are reasonably thing and will warm up fairly quickly unless the ground temp is very low.

Ice will not form on the fan blades during takeoff for the same reason it won't form on decent.

The aircraft has de-icing capabilities for in-flight de-icing of critical control surfaces.

[This message has been edited by NM (edited Dec 08, 2003).]
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