eng anti ice

[ssflying]

Most manuals state that at temperatures below -40c ,there is no need to switch on the eng anti ice,while in cruise.Are there any exceptions,cause i have always felt uncomfortable keeping the anti ice off in visible moisture,at temperatures beloww -40,specially in the tropics where the tropopause is around 52 thousand feet and we encounter active cb cells at 39000 ft.Could someone just clear away this doubt.thanks

[dhardesthard]

If I were you, regardless of what the manual says I would turn on the Engine anti ice in visible moisture irrespective of the temperature.

[de facto]

[QUOTE][irrespective of the temperature/QUOTE]

Debatable but no time ,need to rush to work:hmm:

[CanadaKid]

ssflying,

"Research has shown that strong convective weather (thunderstorm activity) can lift high concentrations of moisture to high altitudes"

AERO - Engine Power Loss in Ice Crystal Conditions (http://boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_03_4.html)

AERO - Engine Power Loss in Ice Crystal Conditions (http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_03_2.html)

[LeadSled]

Folks,
There are several things here.
(1) Do what the airframe manufacturer says in Limitations.
(2) Using engine anti-ice below -40C will not do any harm, just a possible but very minor loss of thrust --- and in some types you will have auto-ignition by whatever name on -- might be a plus.
(3) There are big temperature changes around Cb/Ts, just because you "were" experiencing temps. of less than -40C, doesn't mean you can't run into a wall of rising warm (relatively speaking) air.

Summary:
If you have the slightest doubt, and no limitations will be exceeded, ENG. ANTI ICE --- ON.

Tootle pip!!

[westhawk]

I seem to recall this very subject be discussed a few years ago with regard to some high altitude engine flameout events involving The Beechjet 400. (now known as the Hawker 400XP) In those cases, ice crystals encountered in (seemingly) clear air have been identified as the cause of the flameouts. AFM procedural revisions were issued to address the problem. Activation of engine anti-ice when in the vicinity of convective activity (even if in VMC) is now required.

Several large airliners equipped with certain models of GE CF-6 series engines have suffered flameouts as the result of ice crystal accretion as well.

The conditions requiring engine anti ice use vary by specific airplane and engine type, so a universal policy is not practicable. The proper procedures and conditions for engine anti-ice operation will be contained in the AFM. In some airplanes where maximum cruise thrust may be limited by ITT or N2, engine thrust reduction may be required prior to engine anti-ice activation. In some circumstances of WAT, this may necessitate a descent to an altitude where the reduced thrust will sustain a safe minimum airspeed.

I found this 2008 Flight Safety Foundation (http://flightsafety.org/asw/jun08/asw_jun08_p12-16.pdf)article on the subject interesting.

westhawk

[Capt Claret]

Most manuals state that at temperatures below -40c ,there is no need to switch on the eng anti ice,while in cruise.Are there any exceptions...

There is no such relief in the B717 AFM. ENG A/ICE required in visible moisture below 6 degrees TAT, or when icing visible on airframe.

I've seen significant ice on the windscreen at up to 15 TAT. :ooh:

[ssflying]

The A320 manual states Engine Anti ice must be on during all ground and flight operations when icing conditions exsist ,or are anticipated except during climb and cruise when the Sat is below -40C.I am wondering is to do with the nature of ice crystals at temperatures lower than -40C,but like you have written near convective weather significant moisture is there,and i do keep the anti ice on as a precaution,however a lot of training capts point out the sat to me as below -40C.So i needed some hard logic for my action.thanks

[tightcircuit]

Boeing have recently given some advice on this. There have been a number of unexplained flame outs over the years and the subsequent investigations could find no cause. It is now thought that it is due to ice crystals melting on contact with engine parts and cooling them to the extent that the water re-freezes on parts of the engine that the anti-ice can do nothing about. It was recognised several years ago that this could be severe enough to cause flame out in smaller engines but it is now thought that it can affect big engines the same way. Of course the ice melts again at lower altitude so is not apparent later. Turning the anti ice on has beneficial effects even if it does not stop the ice forming. The increased bleed air makes the engine more stable and as mentioned above turns on the ignition in a lot of models.

One of the danger signs is seeing moisture on the windshield even at temps below -40. This is not super cooled water but the very fine ice crystals melting on high speed contact with the heated glass.

Boeing now also recommend that in conditions such as these you put the wing anti-ice on as well, but only below 22,000ft in the descent. This again is to increase the bleed air take off. They don't recomment the use of wing anti-ice (unless for its proper pupose) any higher because there may not be enough bleed air available for other systems that need it.

The other obvious advice is to avoid areas where this may be a problem (ie as stated above, near convective cloud at high levels) or if already in them get out sharpish.

TC