B737-400 Engine Anti Ice Usage

[Pie-let]

Will it be detrimental (in the long run) to any system if engine anti ice is used above 10oC TAT? Lately there were so many pilots (in my company of course) continue using them until 13-14oC TAT and worst some say as long as they THINK they need it especially on descend on idle power. So the question now is, if this is what we all think, isn't it better to throw what Boeing says out the window and instead of all the limitations, why doen't Boeing just say USE OF ENGINE ANTI ICE IS AT THE DISCRETION OF THE PF (or PNF).
Thanks!

[Pie-let]

No help? Anybody please........... Thanks!

[Sonny Hammond]

Cant answer that one,

But I have seen ice build up, albiet small amounts, on the wipers below -40 SAT. I think the anti ice should be on in this case (airmanship?), but other disagree (not all though)

?!?!

[lomapaseo]

No help? Anybody please........... Thanks!

I sincerely doubt that the answer resides in this community. Boeing has the responsibility for providing operating procedures for operation wityhin the defined operating icing envelop under Part 25 of the FARs. These concerns take into account both the aircraft and the engine needs, including the engine inlet.

The engine gets into the act via not only its ability to generate heated air for use to control ice on the aircraft (including the engine inlet) but also the idle RPM used to control ice accumulation on the front surfaces within the engine (spinner, fan blades, struts etc.)

The thermal and energy balances for all this are assessed by Boeing and promulgated via the Boeing operating procedures. While heat is normally your friend in icing conditions, too much heat may lead to premature fatigue of internal baffles etc.

Since I don't really understand why your question I can only point you in the direction of Boeing for a credible answer.

"the iceman commeth" and now leaveths

[Pie-let]

Thanks a lot for your views. I totally agree that Boeing has definitely did all the icing test whether at idle or powered descend.

[quid]

At MAX power, there's a lot of very hot air going into the system. At some point, it's hot enough to do some damage....perhaps softening the metal or doing some long term structural weakening. At idle, the temperatures are much lower.

But....in most cases the pilot is much too busy to use a "sliding scale" of TAT limits for it's (anti-ice) use depending on the power setting...so only one TAT "limit" goes in the manual. Therefore, a "one size fits all" limitation is published.

The TAT gauge is not calibrated like a Rolex, and may be off a few degrees. So 11C is not going to melt any systems, nor is 9C going to be perfectly OK for the life of the airplane. A little common sense has to come into play here. I've seen on occcasion (on descent and approach where the OAT and IAS vary continually) crews turn it off at 11C, on at 9C, back on at 11C, etc. This is overkill.

The very few conditions where ice can form at 14C are very short lived, and very little ice can acccumulate. This again is overkill.

I'd suggest respecting the published limitations.

[Pie-let]

Thanks a lot once again guys. Really appreciate your views and explanations. Happy flying!

[eng1170]

From an engineers point of view, I know that the leading edge anti-ice system is controlled by temperature and the anti-ice valve will open/close at a certain temp (the fig 110 springs to mind but am not 100% sure)

However I cannot quite recall, but am fairly certain that the inlet anti-ice valve also has a temp sensor in the duct, before the valve if memory is correct, and this if overheated will also close the valve. I think it would take a considerable amount of time to cause any real fatigue problems as a result of excessive use provided that the system works correctly - i.e temp sensors work and that the valve hasn't been locked out.

I would however also add to what has been mentioned, that Boeing will have assessed all eventualities and would only publish advice/recomendations that are prudent in operating the aircraft.

Just as a slight aside but not to far off this thread - as pilots does anyone know if there have ever been cases of 737's with CFM56 engines that have flamed out on descent at idle power, in heavy precipitation, even though the spinner is now rounded as opposed to conical?

I had heard/read that it may of been the cause of the loss of an aircraft recently - was it in the Far East, aircraft finished up in a river, not many casualties?

[fruitbatflyer]

Further to the question on whether leaving it on to 13 or 14 degrees will damage the system, I very much doubt it, tho' how do these exponents ignore the FMS message 'TAI on above 10'?.
I don't have a copy of the MEL in front of me, but recall that if an engine antice valve is stuck or locked open, the operating limit is 38 degrees OAT. When one considers that you would only get such a high temp at or very close to the ground, the implication seems to be that even at takeoff power, no metal will melt.
This is not to condone deliberately exceeding any limits, tho' I did once have an argument with a sim instructor because he set up 11 degrees in 'fog' on the ground and I selected it on while taxying out (to see if it worked) because I figured we would be in 'ice' by the time the gear came up. Sure enough he had jammed the antice valve shut and was setting us up for a flameout and was right royally pissed off when I taxied the sim in for 'rectification' thus thwarting his rather obvious scenario.
Having said all that, the 10 degrees limit is probably conservative.
I know that I am guilty of forgetting to turn it on during climb until about 5 degrees, with no sign of any engine malfunction.

[Sonny Hammond]

Who hasn't forgotten it?
It will do no damage but pilots being pilots want black and white rules of operation....a bit of logic will settle this matter fairly quickly. (I think its called airmanship...whose heard of such a thing????)

[Groaner]

To eng1170;

It was a 737-300 I believe, ended up in a river in Java, Indonesia.

I suspect it was not due to icing, but I recall it being attributed to extremely heavy precipitation (of the rain sort) on flying through a tropical downpour on descent at flight idle causing both engines to snuff.