Using engine anti-ice when dewpoint spread 3 degrees or less

[teesix]

How many operators out there use engine anti-ice after engine start when OAT is +10 C or less and dew-point spread is 3 degrees or less, regardless of visibility or precipitation? And why or why not?

[411A]

Generally do, in the L1011.
Not +10 however, plus eight.
Not just after start however, on the parallel just before (or after) extending flaps.
And no, doing everything before taxiing is not my idea of how it should be done, unless the intended taxi route is very short.
Why do I use engine anti-ice?
Because it's there to be used.
However, if the visibility is reduced, on it goes just after start.
Seems prudent to me.

[Rainboe]

Never used the temp/dew point in the decision process. The books just say 'visible moisture'. That's good enough for me.

[Intruder]

The 3 deg Temp-Dewpoint spread is part of the definition of "visible moisture" in our FHB (747 Classic/GE). We use nacelle anti-ice in that situation.

Since the air pressure drops somewhat as the air is sucked into the intakes, it is possible for moisture to condense and freeze as it cools below ambient. At that temp there is seldom a problem with any reduced thrust due to A/I, so it's a good idea to use it.

Some engines/installations are more susceptible than others. Follow the guidance in your books.

[teesix]

Thank you, Intruder! Exactly my point why it is important to use engine anti-ice when the dew-point spread is 3 degrees or less! I belive I have read that the combination of high engine RPM and low airspeed is the key here.

[Rainboe]

I have never seen this. My B737 Operations manual says no such thing. Previously my B747 Flying Manuals for RB211 and P&W models (747-100,-200 and -400) had no such definition. Simply +10C and below and visibility 1500m or less with visible moisture. I have never heard this 3 degree split mentioned.
I'm not saying it is wrong, but no engines are experiencing any problems when not operated that way!

[Dani]

There are different operators that handle the anti-ice thing differently. But it also depends on the aircraft. Dew point spread is a very common way of defining visible moisture, but always comes as a combination with something, i.e. OAT.

Some airlines define it with a visibility (say 1.5km) plus a temperature. If your spread is small, chances are that you have bad visibility. This of course can only be obtained close to an airport (where dew points are regularly transmitted).

[oldebloke]

The temp/dewpoint 3degree spread is a holdover from the first Jet era..The DC8/9 used this as an antiicing guide(pratt witneys).The vis moisture below plus 8 was used at this time.After the 'Palmair'crash at Washington the FAA went to a straight Vis.moisture below plus ten,although I see in some of the business jets manuals plus 8 is still a reference..
Cheers:ok:

[Rainboe]

Dew point spread is a very common way of defining visible moisture
Common? Where? I'm interested because I haven't heard it before- not on Boeing equipment. Most of the world has not been using that, and there are no extraordinary cases of engines conking out with icing. The common definition is as I outlined with no temp/dewpoint spread. So what equipment uses that definition?

[lomapaseo]

The KISS principal should be followed

The idea is not to get pilots to think too much, else they don't read the manuals. The safe side to be on is the 10 degree safety bar in visible moisture. As was stated earlier when engines suck they depress the temp in the inlet.

Lots of problems with ice forming in engines and not on the wiper blades etc.

When I last checked, all the manuals for consistency in the big iron recognized this. I'll keep my eyes tuned for changes in this forum and check this out if the manuals are not consistent.

[airbond]

Agree with rainboe.

Also never heard of this! Certainly not on any boeing aircraft I have flown.

Plus 10 degrees TAT and below with visible moisture is the criteria.

[CoolHandleLuke]

This is how my OM B defines Icing Conditions (Fokker 100)

On ground icing conditions are present when OAT is below +6 deg C and

Spread is less than 3 deg OR
Visible moisture is present OR
Taxiways and/or runways are contaminated or wet


In flight icing conditions are present when TAT is below +6 deg C down to and including -25 deg C AND visible moisture is present.

... it may not be like Boeing but I most certainly still will be going...:ok:

[Rainboe]

But if it's not Boeing, why would you want to be goeing?

And what about the bit between +6 and +10 deg C? Why would you Fokkers be free of icing there?

[airman13]

they are
1.atmospheric icing conds. when temp is below +5*C on ground (OAT) or below +7*C in flight (TAT) and any moisture observed ,visibilitiy below 1 mile or any precipitations etc...
2.ground icing conds. when OAT is below +5*C and on taxiways or runways it exists patches of water ,slush , snow etc.

now,before performing the de-icing / anti-icing, you have to take in account the real temp.(necessary for type of fluid and ratio) and HOT (hold over time), wich depends of temp and the weather(freezing fog, rain, snow ,sleet) and HOT starts at the same time with the beginning of de-icing operations.

[lomapaseo]

Airman13

Most of this thread is about engine anti-ice.

Did the post you made above reflect also the sane conditions for engine-anti-ice as for the aircraft in general?

What aircraft does this apply?

[Rainboe]

airman13- there is absolutely no point in quoting your types definition of icing conditions without saying what type you are talking about!

[airman13]

Lomapaseo,

I've just tried to emphasize the difference btw ground and atmospheric conditions.

[Jamesel]

Hi, for my 2 cents worth.
For about 5 years, around the turn of the century, on our Jurrasic 737-200s the company SOP included the procedure of Anti-Ice ON when OAT at +10 C or below and dewpoint within 3 degrees. I was told that this was a problem on the 727, mainly the centre engine, and with some of our tech guys having a wack of three holer experience, the same limitations were applied as a precaution. Around 2002 IIRC, this was dropped with no noticeable problems after the change, though I think the JT8D made and ate a lot more ice under normal ground operations than most people realise.

[md-100]

MD-80 FOM says

" use engine anti-ice after engine start when OAT is +6 C or less and visible moisture is present OR when dew-point spread is 3 degrees or less"

[CoolHandleLuke]

But if it's not Boeing, why would you want to be goeing?

Because my company has never bothered to ask me what type of A/C I would like to fly.... they are soo insensitive to the ambitions of a modern pilot/aviator.:{

And what about the bit between +6 and +10 deg C? Why would you Fokkers be free of icing there?

I don't know... why would Boeings be more prone to icing??


On a more serious note....

It seems to me that in aviation there are SOPs based on solid scientific facts and there are those based more or less on religion.

Maybe this difference +10 and +6 deg is based more on religion than on scientific findings.... This is just a thought from someone who has just the minimum of knowledge on these issues.:\

So my question to all of you is: Could it actually be possible that it doesn't really matter if you select engine anti ice at +10 or +6? Or is there actually a difference between different engine types and how prone they are to icing?

[lomapaseo]

So my question to all of you is: Could it actually be possible that it doesn't really matter if you select engine anti ice at +10 or +6? Or is there actually a difference between different engine types and how prone they are to icing?
Yes!!!
But the differences are more in the damage than in the onset of icing. Either way, the concern is that the pilots start thinking that, hey, I never had any problems before so it must be allright. Or that it's a Boeing vs an Airbus, or more likely a GE vs a Pratt or Rolls. What they have no way of knowing are the subtle variations in the sub modules and installations that make the real difference.

Not wanting any crashes period, no matter who was the manufacturer, they simply recommend the 10C as the "safe number"

Now if the manufacturers should find that they are being out-guessed by people without the real design knowledge, this will just encourage the Feds to step in and mandate a rule change (hint, hint)