Proper Use of Engine A/I
Gentlemen:
Please, read the SOP. Stop listening to all the nonsense (feel free to substitute another eight-letter word).
The following applies to P/W JT8D as well as CFM as well as IAE2500: (Please, please, please...in the words of James Brown...read the book to confirm the following.)
Engine anti-ice is to be used when icing conditions exist or are anticipated. (Note...the term is "anti-Ice", not "de-ice". I'll refer to this notion, again, in a moment.)
Now, since we pilots are basically stupid idiots, 'icing conditions' are defined for us, since the engineers doubt we know what that means.
If you're on the ground AND the temperature is +10 or below (+50F)...(note, it's not 'below' +10...it's +10 or below.) AND you're in visible moisture (which is defined as 1 statute mile or less visibility in the case of fog/mist, if not actual precip falling) OR you're taxiing over moisture (like packed snow, water puddles, ice, etc)...THEN you must have the Engine A/I on.
To simplify the above paragraph, consider ANY moisture a threat when the temp is +10 or below. (This includes temps at -40 and below, too, by the way!)
This covers the 'on-ground' situations.
Now, let's talk about in flight. Again, the engine anti-ice is to be on when icing conditions exist or are anticipated. This means when you're in precip (or inflight visibility is 1 statute mile or less...or any kind of visible moisture, for that matter) AND the TAT is +10 or below. This includes if the SAT is -40 or below. (Yes, really, it does!!!)
There is an exception to this inflight rule. If you are climbing or cruising AND the SAT is below -40 (If you're exactly at -40, then you can't use this exception. It's gotta be colder than -40 SAT!), AND you're not in, around, amongst CBs, then you can turn off the engine A/I.
To clarify...you're cruising at FL 350 at a TAT of -42 but
you're picking your way through CBs, THEN YOU HAVE TO HAVE THE ENGINE A/I ON!!!
If you're cruising at FL350 with a TAT of -42 and you're in cirrus...no need for engine Anti-ice. HOWEVER, once you begin your descent out of FL350 (assuming you're still in the cirrus, you need engine anti-ice (because you no longer can take advantage of the climb/cruise exception...you're now descending)!
Now, the difference between anti-ice and de-ice: I can't tell you how many times I've flown with well-intending, good-natured pilots who look out the window...maybe looking at the windshield wiper nuts or Ice Probe or whatever...and say, "Gosh, we're not picking up any ice. No need for engine anti-ice. We'll wait a bit to see if any builds up before turning on the engine anti-ice."
Their logic is that the windshield and probe are at a 'low'pressure' station of the fuselage. Thus, those areas will be the first to pick up ice.
Ok...well, the engine inlets are low pressure stations, too. (Duh!!!!)
Most SOPs explicitly warn against waiting to turn on the engine anti-ice until ice accretion becomes evident. To do so is a very dangerous practice.
Please don't listen to these well-intentioned pilots. I know, they're trying to save fuel...which is a big consideration these days. But, instead read, re-read, understand when and how to use engine anti-ice. It's all very simply-stated in the book.
Safe flying!!!
PantLoad