PPRuNe Forums - Anti-ice below -40 sat

PPRuNe Forums (https://www.pprune.org/)

- Tech Log (https://www.pprune.org/tech-log-15/)

- - Anti-ice below -40 sat (https://www.pprune.org/tech-log/501576-anti-ice-below-40-sat.html)

Anti-ice below -40 sat

Engine TAI must be on when icing conditions exist or are anticipated, except
during climbs and cruise below -40C SAT.

There is no ice accumulation below this temp., but why should be used during descend?

I never asked this question and never read explanation, but I think it's quite obvious: You will inevitably hit icing conditions during descent in clouds, and you don't know when exactly. So, keep it on and you will never miss it.

I think it has something to do with the fact that climb and cruise are conducted with a high N1 while a descent is done at idle.

If there are no clouds on the descent and you can see that fact you don't need it,

Also NAI will slow your ROD as descent idle will increase so you may have to adjust to satisfy constraints etc

Also ice accumulation does not occur at temperatures below -40 unless in a CB, By -40°C, virtually all the droplets will be frozen. The exceptions are clouds with very strong vertical updrafts, such as towering cumulus or cumulonimbus, where liquid water droplets can be carried to great heights before freezing.

I believe its to do with high level icing phenomenon.

SKYbrary - High Level Ice Crystal Icing: Effects on Engines

Edited Bulletin regarding flameout mitigation

Quote:

Boeing and # believe ice accumulated aft of the fan during a descent or deceleration may have been shed and ingested into the engine when the thrust levers were subsequently advanced.

Boeing and # investigations conclude the airplanes most likely encountered ice crystals lifted by convective activity prior to the engine flameout. At very cold temperatures near thunderstorms the airplane can encounter visible moisture made up of high concentrations of small ice crystals.

These ice crystals do not cause weather radar returns. Flight crews have reported deviating around strong weather radar returns when the flameout events have occurred. Flight crews have also reported rain on the windshield when the outside air temperature was too cold for liquid water to exist. Boeing attributes this to ice crystals that melt upon impact with the heated windshield, giving the appearance of rain. These types of ice crystals do not accumulate on cold aircraft surfaces

The High Level Crystal Icing knowledge is newer than the -40 SAT rule, isn't it?

The term 'descent' IMHO is misleading. Most planned continuos descents are done at idle. The flameout protection is much less than at high power. Also the introduction of heated air at idle power has less effect on engine power & efficiency. However, IMHO, if you are doing a short descent in say V/S 1000fpm and thus at about 80% of CRZ power you should not need EAI if >-40SAT and in cloud. You are using what would be a CRZ power for a lower FL even though you are descending. It a debatable point, but one where I believe the thinking pilot can read between the lines of the Boeing SOP and understand the reason for what they wrote and adjust their operation with airmanship.

Quote:

That's what I thought for years, but it's not logical: otherwhise the same would count for climbing in clouds. Eventually you will reach 10 degrees, you just don't know when, so EAI on for the whole climb in clouds? Nah...:ok:

Me it's the EXCEPT part of it that gets me confused.What is the reason of not putting EAI during climb or cruise?I found myself using EAI at cruise in visible moisture with SAT below -40

Quote:

except
during climbs and cruise below -40C SAT

that has been made a law, as there a Nigels who would forget to spot the "SAT increase" up to -10C SAT AS they DESCEND....:suspect:

Reference:

Your aircraft's AFM (You might look under Limitations, first.)

Airbus "Getting to Grips with Cold Weather Operations" Page 39.

Airbus Flight Crew Training Manual SI-010 P4/16 31 MAY 12

Fly safe,

PantLoad

It allows an higher margin for ENG flame out. After hours of cruise you will command the engines idle power.

Besides, eventually you will hit icing conditions as temp is increasing.

Because of idle thrust N1 fan speed etc etc. during descent.

Metal parts of donk will be very and will ice up much quicker when descending into warmer, but still icy conditions?