Anti-ice usage

[B777Heavy]

With reference to usage of Engine Anti-ice usage on the B737NG

Engine anti-ice must be used if in icing or anticipated icing conditions during CLB & CRZ until temp drops below -40degrees celcius. Exceptions to this ofcourse is on the descent, where it is to be used even if below -40.

Is this -40degrees(for CRZ & CLB) like a definitive(or conservative) figure? does this mean that the engine WILL NOT pick up any icing at temperatures below -40?

Personally, I have noticed mild ice on the wiper blades below this temperature

What criteria does everyone else use?

Thanks

[Romeo E.T.]

I recall reading somewhere (possibly circular or FCTM) that Boeing warns against using the wiper blades as a means for determining icing build up, as the wiper blades actuall cause an area of stagnant air underneath them.

the attachment bolt is a much beter indicator, or if fitted ..an ice detector

[BOAC]

Covered somewhere else here - based on the 'physics' of water vapour that below -40 the amount of water vapour in air is very small. Does NOT allow, however, for standing wave and strong convection which can carry water-laden air far into the sky, well below -40.

[shlittlenellie]

The air stagnates below the wiper blades and moisture run-off tends to collect there. Once the air temperature is below freezing, the collected moisture freezes, unsurprisingly. It will then remain there until it melts; either in direct sunlight or more often in the descent (after n hours) when the air temperature rises. Ice often forms under the wiper blade on a CAVOK day due to condensation on the nose running back.

Practically, ice below the wiper blades on a 737 is not a useful indication of airframe icing.

Ice on the wiper bolt is better and severe icing is often indicated by icing on the windscreen on the middle and outer sections of the front panes. Next time you see it on the bolt or window, check the leading edges and then apply wing anti-ice and watch the ice fly off.

Have a look here Ice & Rain (http://www.b737.org.uk/iceandrain.htm#Airframe_Visual_Icing_Cues) with thanks to Chris Brady.

[411A]

Covered somewhere else here - based on the 'physics' of water vapour that below -40 the amount of water vapour in air is very small. Does NOT allow, however, for standing wave and strong convection which can carry water-laden air far into the sky, well below -40.

Absolutely correct.
Switch the engine anti-icing on...and leave it ON, if in doubt.

Leave the the test pilot duties to...test pilots.
That is what they are paid for...big surprise.:}

[B777Heavy]

Thanks for the replies...

hmmm....makes alot of sense....wipers are not a good indication!!

After posting the initial post, I googled anti-ice and came up with a NASA website which says "ice essentially forms at temps between 2degrees celcius & -20degrees celcius". So the -40 maybe conservative after all.

[GlueBall]

-40degrees celcius . . . is the same as -40F, so in this case it wouldn't be necessary to say celsius. Incidentally, there's no money out of your pocket to run engine/nacelle anti ice, or is there? :ooh:

[babotika]

There is actually, an increase in fuel consumption of 2-10% depending on configuration.

If memory serves this is due to bleed air being diverted to the anti-icing system.

S.

[aterpster]

Absolutely correct.
Switch the engine anti-icing on...and leave it ON, if in doubt.



Absolutely! And, in spite of the Green World we now live in, sometimes idle thrust descents are not a great idea. And, if it is at all turbulent, continuous ignition as well (some aircraft require that I believe).

[PantLoad]

BOAC and 411A are correct! May God bless you both.

I used to have all kinds of trouble with the numb-nuts who never read the SOP...or the FCTM. This isn't difficult, people! Just read the manuals....
They tell you the definitive skinny on what is correct.

Fly safe,

PantLoad