ICE crystals

[alistomalibu]

Hi

Flying through supercooled water means ICE formation...(That´s nothing new for us...)
Could we say the same for flying trough ICE crystals?
I dont mean to have ICE formation on aerodinamic surfaces while flying through ICE crystals conditions.
But what about the hot sections of the engine?

Thanks
Alejandro
Argentina

[Rainboe]

No. Below -40 degrees C, ice does not form anywhere on the fuselage or engine. It is practice to never turn on engine or airframe anti-icing below -40 degrees C. Supercooled water cannot exist at below -40 degrees C as far as conventional wisdom says.

[falconer1]

considerable research going on since quite a while..

and there have been engine problems that were presumably traced to "ice crystals"...small & large jets...

see the Boeing AERO article below..

me, still not sure whether that phenomenon just seems to pop up nowadays, because we may fly a tad too close to some convective weather at altitude at times..for whatever ill-advised reasons..

AERO - Engine Power Loss in Ice Crystal Conditions (http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_03_1.html)

can't help the feeling that these things have always been around, but maybe in earlier times farther away from planes....( remember the microburst debates & training and what you have in the 70's and early 80's...well CBs have produced microbursts before humankind..'s just that not so many folks had tried to land or take-off during thunderstorms before..)

but maybe I'm all wrong and it can be all attributed to "climate change";)

[safetypee]

See the links in this post http://www.pprune.org/tech-log/376345-air-france-a330-accident-6.html#post5027449

Ice crystals will normally bounce-off both cold and heated surfaces; however, on some heated surfaces if the crystals are slowed down by airflow disturbance, closed curves, etc, then depending on several variables (particularly heat flow) then some of the ice may melt and the water traps other particles resulting in ice accumulation.

This is not normally a problem for engines except in exceptional circumstances, i.e. near large Cbs.

[Ocampo]

...the correct action would be to start a descent and turning on Engine Anti-Ice protection?

BTW, there have been lots of rumours about what happened to WCW708 in Venezuela, but no "official" response to the question "What happened to that airplane?". Although ice has always been on the table as a cause of the crash.

[shortfuel]

No. Below -40 degrees C, ice does not form anywhere on the fuselage or engine. It is practice to never turn on engine or airframe anti-icing below -40 degrees C.

If I were you, I'd do my homework before spreading falsehood.
The problem among our pilot community is that we actually know little about ice particle (or ice crystal) icing.

For those flying on the bus, FCTM says to turn Engine Anti Ice ON when flying near CBs even if SAT is <-40°c ! that's mainly because of ice particle icing (e.g. in an anvil).

Thalès pitot probes -AA (AF447) series seemed very sensitive to that particular phenomenon, given their ASR history.

Most Ice particle types are not detectable by Wx radar. When in it, pilots are often misleaded by the sound of melted ice particles on the windshield (if any) that is wrongly interpreted as rain or hail...

Ice particle phenomenon is quite a new study field (less than 5 years). Those MET conditions being very difficult to recreate in a lab, thus modeling.
In flight, as said by safetypee, it's usually around deep convective cells.

I suggest these readings:
Ice particle threat to engines in flight (http://www.skybrary.aero/bookshelf/books/581.pdf)
FSF article about Ice Crystal Icing (http://www.flightsafety.org/asw/jun08/asw_jun08_p12-16.pdf)
PPS by Jeanne Mason, a (the?) specialist of ice particle icing (http://www.captainpilot.com/B737/IceCrystalWeatherThreatToEngines.pdf)

Correct course of action...
I would say it depends on the icing severity. Sometimes it could as subtle as an anomalous TAT reading that you won't even notice in cruise.
In a case of powerloss, with EPR engines, it could be difficult to discriminate between an actual icing of compressor stage(s) or just a severe TAT cloging.

I would say, (E/AI ON, disconnect A/THR) get out of those conditions first (descend most probably), see after.
But I am not Mr Airbus or Boeing, so...:rolleyes:

[ATPMBA]

The Wall Street Journal had published an article in its April 7,2008 edition titled "Airline Regulators Grapple With Engine-Shutdown Peril." It's about the ice in the engine. I think these may of been the cause of an engine flameout in a Lear 25 years ago in a flight from the Bahammas to Boston for a company I had once worked for.

[Rainboe]

The problem with Pprune is there are so many people here that if you say white is white, some smart Alec will prove that in certain circumstances, white is, actually, black, don't you know? We now get Airbus advice, and me told to do my homework, when such advice does not appear in the Boeing handbook. We are given unproven evidence from 2 crashes where icing may have been a factor, but it is unproven, and anybody quoting that as support for a wider definition is skating on thin ice! If you pardon the expression.

The OP asked a simple question which has been overcomplicated by numerous 'experts' here, quoting a totally different type. A little research about the OP would reveal he is evidently learning from a Boeing POV, not Airbus, and that was where my answer was based. There is no need to needlessly complicate for a foreign speaking poster- he was asking from an inexperienced learner working from a Boeing perspective, not Airbus, and that was the perspective my answer. So thanks for the lesson, but not needed, or desired, in this thread.

Now how does Antonov and Ilyushin play it then? Any advance on Tristars and Embraer? It's getting frightening to answer any queries here because there are always pedants who will prove your answer wrong for a type that is not even being asked about.

[punkalouver]

I think perhaps the problem is with you. I believe you said "Below -40 degrees C, ice does not form anywhere on the fuselage or engine". Someone could misinterpret with unfortunate consequences.

The first line in the Boeing Aero magazine says "Since 1990, there have been at least 100 jet engine power-loss events on both commuter and large transport airplanes, mostly at altitudes higher than 22,000 feet, the highest altitude where airframe icing is expected to exist.". Some have been below -40. Then it goes on to explain the ice crystal phenomenon.

The Beechjet appears to be particularly susceptible.

I suggest you read and then realize that it is a strength to be able to admit when you are wrong.

[MU3001A]

The Beechjet appears to be particularly susceptible.

It's not the Beechjet per se but its engines, JT15D's that appear susceptible to the ice crystal phenomenon. Same probably goes for the engines on the big transports, rather than the airframes they are attached to.

[punkalouver]

It's not the Beechjet per se but its engines, JT15D's that appear susceptible to the ice crystal phenomenon. Same probably goes for the engines on the big transports, rather than the airframes they are attached to.

Very correct. But I am not sure if it is just a particular dash number of that engine that is susceptible and happens to be on the Beechjet(maybe only on the Beechjet) so I didn't want to say that engine in particular.

Thanks.

[PantLoad]

Not quite correct: Ice cannot form when temps are below -40c.

Please read the Airbus FCTM with regard to this. You will find that
the procedure is to NOT use anti-ice systems during climb or cruise
when the OAT is below -40C except when flying in areas of CBs.

So, with this, there is to be noted exceptions to this "minus 40 rule".
First, this applies only to climb and cruise. Second, this applies only
if not in the vicinity of convective activity.

Other posts, so far, list the reasons why......


Fly safe,


PantLoad


post script.....It was SOP at my former company (I've retired several years ago.) to follow the above-mentioned rule. And, we flew the Boeing
(with JT8D, CFM 56, and CF6) as well as Airbus (with CFM and Pratts on the 330).

By the way, there was an excellent article from Airbus....will try to find it...about flameouts at high-altitudes on CF6s. What was happening
was, during initial descent, at temps well below -40C, the engines were
flaming out. If I recall the article, it mentioned that most of the events
occurred in tropical climates where CBs were present. In every case,
engine anti-ice was not selected at top-of-descent....when in visible
moisture...but OAT less than -40c.

Interesting.....

[Rainboe]

I've been flying 737, 747 and 757 for 32 years, and procedure in one of the worlds largest airlines has always been, 'below -40C, anti-icing is not needed, unless you are in a descent, where it may be switched on in anticipation of entering icing conditions'. That, is standard procedure. I don't recall it ever failing in all that time.

I really have no idea about special Airbus definitions or requirements. I still don't understand thottles that don't move. The OP is asking about Boeings as evidently that is what he is studying. If you are going to take the trouble to answer his query, it is worth seeing where he is coming from and not confuse him with other types' special procedures.

[foff]

I've been flying 737, 747 and 757 for 32 years, and procedure in one of the worlds largest airlines has always been, 'below -40C, anti-icing is not needed, unless you are in a descent, where it may be switched on in anticipation of entering icing conditions'. That, is standard procedure. I don't recall it ever failing in all that time.


hi,
you might have followed a wrong SOP during 32 years as I did until now on both Boeing & Airbus. Same with wrong check-list amended after accidents. By the way, what I teach to my experienced trainees is to follow the SOPs unless you know or have a well founfed reason to think that it is unsafe. Some pilots write the books and others have to cope with bad literature in the air.

[shortfuel]

The OP is asking about Boeings as evidently that is what he is studying

I didn't know that Boeing was an engine manufacturer, as you really insist that is a type related question...
Question was about possible crystal icing on hot sections of engine.
And don't worry, your SOP will be amended soon by Boeing (if not already), you might even get a tech bulletin on crystal icing.

[lomapaseo]

I didn't know that Boeing was an engine manufacturer, as you really insist that is a type related question...
Question was about possible crystal icing on hot sections of engine.
And don't worry, your SOP will be amended soon by Boeing (if not already), you might even get a tech bulletin on crystal icing.

I don't mean to pick the above quote apart, just to add on.

Boeing and Airbus etc. both have the advantage of knowing all the ins and outs of engine icing just simply due to their oversight of the various engine manufacturers products.

Ice is not unique to any one engine, however the response of the engine to ice may be unique to where it does accrete and how big it is when it sheds. I use the word shed because with today's gas turbines it doesn't melt before it is blown off the surface simply by windage. In some cases the ice buildup and shed is big enough to damage the compressor blades and cause enough damage to cause an engine stall or rundown in RPM (flameouts are rare). In other cases if the ice blocks an important engine sensor the engine begins to lose its mind (FADEC is confused).

There isn't much you can do to avoid ice crystals if you are flying over the top of weather. The engine manufacturers through Boeing and Airbus can advise you on how to handle the engine once it has exhibited symptoms so forget about all these words of wisdom (including my own) and follow the updated procedures.

I will admit that I was confused about the original question and its use of the word "hot sections". I tend to associate that definition with areas in the engine behind the burner. However if the question was about metal temperatures on probes and vanes simply above the melting point of ice > 32F then this thread discussion applies.

[shortfuel]

Well said lomapaseo :ok:


Here is just another extract:

The actual mechanism for engine powerloss takes many forms, depending on the engine. Each engine’s overall
stability is a balance between compressor stability, combustor stability, and the fuel available for acceleration.
The component that is the mechanism for failure is the element with the least margin to cope with an ice ingestion, and varies by engine type. All of the following mechanisms have occurred:

• Engine surge and stall: ice shed into the compressor can drive the engine into stall due to the combined
effect of the lost inertial and heat energy to the ice, and the inefficiency of the airfoils having ice on them.
The scenario begins with a compressor surge (a sudden flow reversal) followed by stall (engine rotor
speeds decay), as airflow is reduced due the presence of one or more compressor stages with localized
airflow separation. The combustor remains lit, and due to the lack of airflow, exhaust gas temperature
(EGT) typically rises quickly.

• Flameout: quenching of the combustor following the ingestion a quantity of ice.

• Engine damage: engine blades and vanes can become damaged as shed ice impacts them. Typically minor blade tip curl is the only damage present owever, rare instances of blade release have occurred. Damage has also occurred without any other symptom.

The event data indicate that following the powerloss, all engines were restarted. Even in the rare cases where the engine was damaged, those engines were restarted and operated normally for the remainder of the flight. Typically the encounter with high concentrations of ice particles is relatively brief, as inferred from TAT anomaly data...[...]...In all cases, once the aircraft exited the ice particle conditions, and descended to the restart envelope, the engine was restarted.

[MexCrew]

Just to add on to this friendly and interesting query and not trying to be a smart Alec but 'shortfuel' is right, there has been a tech bulleting around for a 'little while'.

- Important excerpts and 'updated procedures' only, cause it would take me all week to try and reproduce it all here, hehe.

_________________________________________________
'From Boeing Ops Manual Bulletin
Number: JDE-8
Dated: June 15, 2007.
Subject: Engine Flameout Protection
__________________________________________________
BACKGROUND INFORMATION

- Boeing and GE have investigated 21 engine flameout events which have occurred on various airplane models since 1991. Investigation of weather flight data and pilot reports associated with these events suggests the flameouts occurred between 11,500 and 33,00 feet in the vicinity of thunderstorms.
- Boeing and GE investigations conclude the event 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 returns.
-These ICE crystals do not accumulate on cold aircraft surfaces.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
OPERATING INSTRUCTIONS

ENGINE FLAMEOUT PROTECTION

Accomplish this procedure when:
- in visible moisture with TAT below -10C near convective weather systems, including thunderstorms, and
- thrust is reduced for a descent or speed reduction.

* * * THE ABOVE APPLIES EVEN WITH SAT BELOW -40C. * * *

PACK HIGH FLOW SWITCH...................................................... ....................ON
(Increases bleed air extraction to improve engine flameout margin.)

NACELLE ANTI-ICE SWITCHES ............................................................ .........ON
(Increases bleed air extraction to improve engine flameout margin.)

Return to a normal configuration when:
the above conditions no longer exist, or
the > ANTI-ICE message is displayed
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

For additional info and details, refer to Flight Operations Technical Bulletin 747-400-55,
Subject: Convective Weather Containing Ice Crystals Associated with Engine Power Loss and Damage, dated August 1, 2006.
____________________________________________________________ _______________


Happy contrails, everyone. Cheers!! =)

MC

[alistomalibu]

Hi

Thanks a lot for your helpful answers.:D
I was reading them and I found a lot of good information with good links.
More answers are welcome...:ok:

[Rainboe]

Well I follow what is printed in my manuals, not quotations from theoretical papers, posted here by anonymous posters. What I gave to the OP was as written in my manuals and that is what I have always flown to, and they have not been amended yet (or failed me or the airline in 40 odd years)!

What you have done is to thoroughly confuse a learner after an uncomplicated answer. How hilarious I am accused of being 'wrong' by people quoting dodgy accident connections and theoretical papers!

[BOAC]

Rainboe - you are confused by the meteorology you learnt all those decades ago. It is true that at temperatures below -40, the amount of water vapour that can be held in air is so small as to render super-cooled droplets irrelevant, and that is the basis for the existing guidance. HOWEVER, in conditions of strong convective or lenticular activity, sc droplets can be carried aloft into temperatures well below -40. Ice crystals are also a threat to engines at those temperatures as you should have read on these very forums. Things HAVE changed. You will do what you are used to over '40 years', of course. Others take note of new information and learn. Out of interest, what do you see as the problem in using anti-ice in relevant high-level cloud at temperatures below -40, apart from a very small fuel penalty and the fact that you will no doubt have noticed over the years that the 'bible' does not say you should not use it?

[falconer1]

would humbly suggest, you try to "get some updates" for your 40 year old SOPs..

to call a Boeing AERO article "dodgy accident connections and theoretical papers"..well, how about you contact Boeing and try to set them straight???

strange perceptions you have..

[shortfuel]

What you have done is to thoroughly confuse a learner after an uncomplicated answer.

Really...? The question (and this topic in general) is actually far more complicated for anyone on this forum.
But that was a good opportunity to review/discover/share thoughts on that phenomenon and its operational impact.

As for the OP, try not to speak on his behalf, that would be a good start.

[MexCrew]

Though your comment wasn't necessarily directed at me, I didn't make reference to a theoretical paper on my previous post but rather a direct quote from the 'Boeing Flight Crew Operations' manual and said 'Bulletin' is still (IE) 'In Effect' so as far as conventional wisdom suggests perhaps a buzz to Tech Pilot or Tech Dept of one's largest airline to ask for Boeing's latest bulletin updates is in order.

Furthermore, I don't think that ice crystals have the ability to distinguish between aircraft or engine types.

Blue skies,

MC

[john_tullamarine]

I'm sure that Rainboe has big enough shoulders to withstand a little critical comment. However, I would ask that we keep criticism to objective comment and not allow it to move into subjective pejorative .. ie "play the ball .. not the player"

[Jimmy Do Little]

For those flying on the bus, FCTM says to turn Engine Anti Ice ON when flying near CBs even if TAT is <-40°c ! that's mainly because of ice particle icing (e.g. in an anvil).

Is there are more current version of the FCTM, or was that a Typo?

FCTM 04.010... (A320) July 2008 Version
FCTM 5.10.5... (A330, A340) 2006 Version

"...CLIMB/ DESCENT
Whenever icing conditions are encountered or expected, the engine anti-ice should be turned on. Although the TAT before entering clouds may not require engine anti-ice, flight crews should be aware that the TAT often decreases significantly, when entering clouds.

In climb or cruise, when the SAT decreases to lower than -40 °C, engine anti-ice should be turned off, unless flying near CBs..."

Also.....

FCOM 3.4.30 (Rev 39)

"...icing conditions may be expected when the OAT (on ground and for take-off), or when the TAT (in flight) is at or below 10 c, and there is visible moisture in the air (such as clouds, fog with low visibility of one mile or less, rain, snow, sleet, ice crystals) or standing water..."

Could we say the same for flying trough ICE crystals?

Someone had mentioned earlier that the query related to Boeing, thus the "Boeing Bulletin" would apply. But, it's interesting to note that Airbus seems to agree (...Ice Crystals...).

Like some other examples between the two, Airbus says "do this, don't do that," Boeing tells you why.

[Rainboe]

Let's try again,
to call a Boeing AERO article "dodgy accident connections and theoretical papers"..well, how about you contact Boeing and try to set them straight???

strange perceptions you have..

Some of you are quoting Airbus procedures and some are quoting from theoretical papers, not official documents. All I see are up-to-date procedures from my OMB Procedures.

I have spent much of a 38 year career flogging up and down over the depths of Africa at night through Cbs, and across the ITCZ in the Indian Ocean. Once below -40C, anti-icing never went on. Even in severe turbulence and precipitation, forget 'near Cbs, this is in them. Until I see my manuals changed to reflect advice, I don't see that a problem has been proved that aeroplanes cannot handle it. Strange and weird some of you chose to respond to this with personal insults! I've spent a career there. I see no problem with current standard procedures and advice. I'm afraid I am too busy working to go reading theoretical papers and unsubstantiated and unproven theoretical possible accident causes. The advice has not let down me or BA in at least 40 years that I know of.

When the manuals change, I will be happy to amend my procedures, but I am not taking anonymous advice from posters who seem hung up on theoretical papers or private accident theories, or trying to use home-grown procedures pending what might be future procedure changes. I have yet to see anything 'official' despite the over-reaction of some of you who don't appear to understand what working to a manual and 'established' procedures means.

I don't intend discussing this further. I have given the official Boeing line. One wishes one hadn't bothered answering in the first place. The chap just need an answer to a simple query- instead of 'yes' or 'no', he gets 2 pages of unproven theories and Airbus procedures!

[PantLoad]

Gentlemen,

Obviously, this has become a sensitive topic....for whatever reason.
So, I will emphasize that we all need to follow our company's SOPs,
regardless of what manufacturers say, regardless of PPrune says.
I'm sure I don't need to explain why the SOP is most important.

I'll say no more, except to answer the question of which issue of the
Airbus FCTM I reference.

It's: A-320 Airbus Flight Crew Training Manual, "Supplementary Information" Section SI-010 P4/16 Issue date: 24 JUN 09.
(This is the latest page issue from Airbus.)


Fly safe,

PantLoad

[Jimmy Do Little]

I'll say no more, except to answer the question of which issue of the Airbus FCTM I reference.


Sorry, was refering to the quote by "Shortfuel" (post #7)

[shortfuel]

Jimmy,
Definitely a typo :E (I meant SAT).



Rainboe,

Telling people that ice does not form anywhere on the engine below -40°C is a falsehood due to your ignorance on this topic (?).
Happy flying in African CBs! But interesting attitude of yours "I did it many times, nothing happened to me".
BTW, there was no personal insult on this thread.

[Jimmy Do Little]

Obviously, this has become a sensitive topic....for whatever reason.

What's odd about this, is that a group of people who are supposed to be trained in CRM, etc, have such a difficult time accepting someone elses point of view when it contradicts their own.

I recall, albeit, from a long time ago "...agree to disagree...but respect each others opinions" What ever happened to that? :confused:

-------------------------------


definitely a typo Figured as much. Cheers:ok:

[Rainboe]

Telling people that ice does not form anywhere on the engine below -40°C is a falsehood due to your ignorance on this topic (?).
Happy flying in African CBs! But interesting attitude of yours "I did it many times, nothing happened to me".

One last time! I have never seen ice below -40C in over 20,000 hours flying, and do not accept it actually forms. Neither does both my airlines, which publish manuals telling me such and a procedure to follow which has been followed and never known to be substandard. My 'ignorance' or your dunderheaded refusal to accept current procedures?

If Airbus has a problem with pitot tubes, I would like to see proof and new procedures. But I know nothing about Airbuses, or any wish to learn!

[shortfuel]

If you can't sustain a contradictory debate, don't bother replying.

I just assumed you were ignorant on that topic (hence the "?"). Nobody called you ignorant.

As far as I know, BA does not edict the laws of physics, do they?

I dont' really care about your company procedures and I never intented to convince you. The OP asked about a MET/physics related phenomenon and you peremptorily answered with your outdated (my opinion) company procedure based on a false statement.

Icing (not supercooled water icing with Liquid Water Content but ice particle icing) can form below -40°c in particular conditions wether you like it or not and crystal icing is a potential threat for aviation ops (and that statement is not from me, it's from Boeing / GE / NASA / FSF...).

[Airbus had many problems with certain pitot tubes, as for the proof, you have google or EASA AD section ;) ]

[Jimmy Do Little]

Rainboe. I agree with you! But, if I had said it, it would have gone like this....

I have never seen ice FORM below -40C in over 20,000 hours flying. Below -40C, I've only ever flown in Clear skys, or Ice!

Ice can form below -40°c in particular conditions wether you like it or not Sorry, I don't agree.

Then, along comes someone (Boeing) and says that we can take that ice (or water vapour) and heat it up; thus melting it within the engine(Simple summary). Okay, turn the Anti-ice on.

Is it that complicated?

Bottom line. Employer pays me $XXXXX per month to fly their airplane, their way. If they want engine anti-ice on below -40c, and they publish that requirment in an approved document (FCOM, SOP, etc), I'll do it. Just keep the paycheck coming.

[Genghis the Engineer]

Oddments:


- It's known that in the last decade or so, there have been 100ish incidents of engine rollback in conditions which are consistent with high IWC (iced water content).

- High IWC is different to icing conditions.

- Experience says that high IWC is not readily visible from a cockpit, and that the instrumentation to detect it is only fitted to a handful of specialist research aeroplanes around the world.

- NASA is currently pursuing a research programme into this. It's in several parts but will include flying one or more research aeroplanes to look into what conditions exist where. An out of date news article here (http://www.physorg.com/news121960528.html) suggests use of a modified S3 Viking, although I have a little inside knowledge which suggests that it'll now be something else - as yet undecided.

- NASA is working with FAA and the Australian Bureau of Meteorology of the programme. This is because they want to look at flying in the vicinity of Darwin where they've got a good combination of ground facilities and weather.

- The concern is about core and compressor stator icing due to partial melting then congealing of iced water crystals. The mechanism isn't well understood but it's believed that where it occurs it takes some time (15 minutes has been quoted to me) to start to get an appreciable power loss. So, you'd have to stay in those conditions for some time.

- They aren't worried about airframe or intake icing - those are well understood, and all airliners have adequate information about their avoidance and treatment. This is something quite new.

G

[MU3001A]

Rainboe: One last time! I have never seen ice below -40C in over 20,000 hours flying, and do not accept it actually forms.I have never seen ice form inside an engine, period and am unlikely to ever do so. Doesn't mean I'm going to wait until I personally experience a rollback or flame out in conditions where ice should not form, or discount the ice crystal phenomenon or ignore manufacturers recommendations to counter the risk.

[BOAC]

Alejandro - now that Rainboe has (finally?) left this thread, may I summarise?

You asked in #1 about a phenomonen (ice crystal icing) about which some posters know nothing because it is not in their 'drivers' handbook' Others do, including major engine and aircraft manufacturers. Good on you for asking. Please take note that it is thought to be a significant occurrence. Manuals will eventually be amended if it is thought necessary. There is information published by various manufacturers which obviously has not reached the third level airlines yet.

It is up to you how you progress this. Keep an open mind and keep asking questions and looking for information.

As a final thought, it is only in the last 20 years or so that the legal requirement for London Taxis ('Hackney carriages') to carry a bale of hay in the back for the horse has been dropped. Progress indeed. It is true that not a single horse ran out of hay in a motorised London taxi in the years the law was in place.

[punkalouver]

A look back at the first post shows that the original question appears to be in general and not about a specific type. Despite claims that it is only from a Boeing point of view, that original poster may go onto other aircraft. Other people reading this thread may be on different types and when they read from a supposedly experienced type that ice is NOT going to happen below -40, they may believe it.

Examples are given showing that engines have been flaming out and aircraft involved in serious incidents much more than previously thought, yet the accusation is made that they are from "dodgy accident connections and theoretical papers" even though a Boeing magazine is quoted.

Then it is said that in 38 years of flying, icing below -40 has never been experienced even though this thread is about unseen icing in engines from ice crystals that don't accumulate on the airframe. 99% of us or more have likely never seen such icing either.

I am going to post a link to perhaps another dodgy accident connection. That is the NTSB. It talks about several of these incidents. One of them, a Beechjet was at FL 380 with a static OAT of -57°C as read in the actual accident report.

http://www.ntsb.gov/recs/letters/2006/A06_56_59.pdf

I think the original poster and others have more than one thing to learn about on this thread. One from a technical point of view and another from a human factors point of view on aviation hazards. And remember, what happens on one aircraft can be much different to what the same effect does to another aircraft. Also remember remember that over the course of your career you will receive much false/misleading information from others that you talk to.

Here are some quotes.

"The Safety Board is well aware of the threat that ice crystals can pose to turbine engines. On June 4, 2002, Spirit Airlines flight 970, a Boeing MD-82 airplane,15 experienced a dual-engine flameout of its Pratt & Whitney JT8D-219 engines after high altitude ice crystals blocked the engines’ inlet pressure probes while the airplane was in cruise flight at FL 330."

"During the investigation of the dual-engine flameout events, it was learned that a general perception exists among flight crews of airplanes that fly at high altitudes that ice is not a threat at the higher altitudes because it is “too cold.” This perception is reinforced by the fact that the ice crystals that are of concern do not accrete on the usual places that pilots look for ice such as the wings, windshield wiper blade arms, or the arm retaining bolts."

"The Safety Board notes that the problem of multi-engine losses of power due to icing is not limited to the JT15D-5 engine and that General Electric CF6-80 series engines have also experienced in-flight losses of power due to internal icing.

[Basil]

I'm pretty certain that Rainboe, like most experienced jet pilots is aware that, when flying in the proximity of convective systems, anvils and the like, all bets re icing are off and whilst I may not (manually for some types) switch on the engine anti-icing I'd be keeping an eye on the parameters.
A lot of the published material is engine specific, e.g. FAA document which refers to <<B767 & B747 aircraft fitted with GE CF6-80C2 and CF6-80A engines >> I note punkalouver's post also refers to P&W.

p.s. Rainboe, that's a pint you owe me ;)

[punkalouver]

A lot of the published material is engine specific, e.g. FAA document which refers to <<B767 & B747 aircraft fitted with GE CF6-80C2 and CF6-80A engines >> I note punkalouver's post also refers to P&W.

p.s. Rainboe, that's a pint you owe me ;)

The NTSB report does make this reference on page 8 of their report:

"The Safety Board is aware of a June 1, 2006, dual-engine flameout that occurred on a Qatar Airways A-330 airplane equipped with General Electric CF6-80E1 engines while the airplane was descending through IMC for landing at Shanghai, Peoples Republic of China."

[Rainboe]

It doesn't happen. It hasn't happened in nearly 40 years of 747 operations up and down African through the ITCZ, across the Indian Ocean through monsoons and hell, and through storms in Asia. BA has been operating up to 114 widebody aircraft on worldwide routes. I've done my share flying them. The rule is below -40, you can forget icing. I've not known of a single case to contradict it- had it happened, we would have changed our procedures. My procedures are as outlined, and as far as I know, BAs are as well.

The proof being thrown at me that it does happen seems to consist of airey-fairey theoretical papers and unsubstantiated accident theories, in particular AF447 which appears to have had substandard systems, but nobody really knows. When the advice and official procedures are changed, I will gladly go along with the new procedures. But until then, some of you may as well save flapping your lips together, because you are spouting unproven theories that I do not accept or believe. Is that clear enough for some of you? I tried to say it nicely, but that's how it comes!

[falconer1]

may I offer, without any hard feelings, some middle ground that we could maybe agree to..

I remember when I heard of the Beechjet events. My first thought at that time was, well, those poor folks obviously must have had some sort of fuel contamination, may be a water and / or strange water/PRIST issue, whatever..

The Beechjet events still do not seem as clear cut, as remember that a short time after that, PWC issued some Service Bulletins for those engines in Beechjets and C-560s, one is half ( single channel) FADEC with hydromechanical back-up and the other fully hydromechanical on the FCU side, and those SBs actually rerouted some hot bleed air to a sensitive part of the FCU that was presumed to maybe have become "frozen", albeit as PWC stated in a high humidity environment..

so the Beechjet events actually may not fall into the "iced compressor" category, but then who knows..

Now to the Boeing, NASA. FSF studies AND some revised AFM info on Airbuses and Boeing etc. regarding possible "Compressor Icing"..

Guess we can agree that the stuff in and close to highly convective weather at altitude is touchy..

could we agree now on the following: new engine technology, that employs highly tuned and efficient compressors, may in fact be more susceptible to airflow disruption by the phenomenon described in the Boeing AERO article than older tech engines....?!

air traffic has increased immensely over the last decades, the altitude bands in which we fly are a tad different from the ones 30 - 40 years ago, and last but not least ( my favorite theory, as you may have found from my other posts), could it be that more airplanes at altitude fly closer to convective weather than ever before ( maybe due to some false sense of safety by modern crews using modern weather avoidance equipment..)???

Now , could all these factors taken together mean, that we start to see stuff, that simply had not been encountered on a statistically significant basis 30 - 40 years ago???

[safetypee]

My involvement with ‘ice crystal icing’ started in the late 80’s with engine ‘rollback’ events involving the BAe146 aircraft; but only with the ALF 502 engine. At that time, the cause of the problem was not known.
As events accumulated, numerically and severity, investigations and tests associated the issue with ‘weak’ engine anti-icing, large Cbs, high altitude (>FL300), and large ISA+ deviations.

Ground tests in engine/icing tunnels together with modeling provided a consistent theory linking ice particles (seen in other work), from which modifications evolved.
Flight tests in European icing conditions repeated the normal icing certification parameters (Appx C) and checked that very severe SLD was not the cause.
Flight tests in / near large Cbs were conducted in Panama to measure atmospheric conditions and induce a rollback; no rollbacks occurred. Subsequent tests in the US in similar conditions did induce a rollback on an unmodified engine and proved the effectiveness of the modifications on another.
These tests are summarized in the ‘Strapp’ report (The Ice Particle Threat to Engines in Flight - http://www.pprune.org/tech-log/376345-air-france-a330-accident-6.html#post5027449) under ‘Commuter Transport Aircraft’.

The essential elements of the theories were substantiated with the work by Strapp, and that of Stromberg (University of Manchester/UMIST), Maltby (BAe/now RR?), et al – Honeywell engines etc, using the BAe146 test aircraft. Fully instrumented engines including one with cameras inside the engine identified ice formation and severity over a range of ‘ice crystal’ conditions.
The relatively small 502 engine suffered ice blocking of the first stage compressor stators which reduced the airflow, rolled back the N2 and thence N1 with increasing EGT. The rollback conditions were only susceptible in a narrow ranger of atmospheric conditions, depended on the duration of the encounter, and engine air off-take – airframe anti-ice, bleed-band setting etc. The conditions were associated with TAT probe anomalies due to freezing, but no pitot problems were seen.

No airframe icing was encountered during these tests – little or no liquid water – classic icing theory. Some light icing was seen on the windshield and wipers where the crystals melted on the heated screen and refroze at the edges; the screen appeared wet / very wet like flying in heavy drizzle.
There were some extremely damaging hail encounters in the tops of the Cbs, but not much fine ice crystal content, this was more in the outflow and anvil regions. Hence aircraft avoiding, or ‘cutting the corner’ around Cbs were more likely to encounter the problem. Interim restrictions on the 146 required Cb avoidance by a wide margin (20 nm IIRC) and subsequently no flight above FL280 in ‘icing conditions’ (< -10C in visible moisture). Problems still occurred due to HF and ‘interpretive’ issues, misjudging the distance to the storm (core centre / edge of the ‘red’) – use of WR, and lack of an airworthiness mandate. Also, the conditions were very difficult to detect. The ‘ice’ cloud structure was very wispy, almost non existent, and gave little or no return on radar.

Following sever multiengine events, ADs were issued and a mandated modification program instigated; all engines were modified by improving the aerodynamic design of the first stage of the compressor and heat flow in the inlet guide vanes, amongst other minor improvements.
The very similar ALF 507 engine was not affected; it had two stages of at the front of the compressor vs one, and was further reinforced by the introduction of FADEC (bleed control).

BAe/Honeywell did liaise with other engine manufacturers who also reported high altitude ‘unexplained events’ – (manufacturers do talk to each other about safety matters). However the nature of the problems on the ‘big’ engines were not the same or severe (at that time) as the 502 engine; the differences are described in the report under Large Transport Aircraft.

Although the ‘threat’ does not appear to be universal to all engines or aircraft, the issues of severity and exposure to ice crystal conditions, the inconsistent nature of the atmosphere, and changes with the ‘high tech’ evolution of engines should not (IMHO) lead to any complacency; it may be that we have yet to see a large enough storm or for someone to misidentify the hazard applicable to thier aircraft.

[Rainboe]

Very good. Nothing more than 'theories' and 'theoretical papers', usually involving other types and engines I don't know! Meanwhile my manuals remain unchanged. I will continue to operate to the official advice in my manual. Can you tell me when it has let the system down? Not 'suspicions' please.

The OP asked a question. It was answered with the official line. Some of you then went off on one with unsubstantiated theoretical stuff usually involving other engines/types. He wanted a simple answer!

[BOAC]

The OP asked a question.- yes inded he did - he asked about something that is not in the engine icing section of your manual ('lifted' verbatim - and unchanged - from the BA 737 Classic manual of the 1980's.)theoretical stuff usually involving other engines/types. - which 'other engines/types' are you on about? Did he specify? I have put my reading glasses on and looked and I see But what about the hot sections of the engine? What do you see?

[lomapaseo]

The OP asked a question. It was answered with the official line. Some of you then went off on one with unsubstantiated theoretical stuff usually involving other engines/types. He wanted a simple answer!

Ah, but there in lies the true power of PPRune Technical Forum. It is not just a PM type one on one but a true discussion forum including drifting "off Topic" now and then and providing useful information to many more than just a single poster. Tis a shame that the thread got personalized, but if one reads beyond the personal coments there is much information and truly balance opinions within.

Typically the opening question is often open ended and subject to interpretation by the readers and responders, hence the broad viewpoints.

[Clandestino]

It doesn't happen.

It happens so seldom that the large majority of the pilots can justifiably say: "It never happened to me." Saying that it doesn't happen at all is somewhat untrue.

I will continue to operate to the official advice in my manual.

Very good, sir. It seems to me that current procedures (inflight restart, unreliable airspeed) are quite capable of coping with possible unfortunate effects of encountering nasty ice particles in large concentrations.

Incidentally, official lines may or may not bear resemblance to real world. Can you count changes of the manuals and procedures during your career, brought on by the demise of the unsuspecting?

[safetypee]

There appears to be some difficulty in recognizing what has previously been theory and is now accepted as repeatable evidence, or that the established facts might apply to range of aircraft and engine types as circumstances change.

An earlier ‘peer reviewed’ article at www.specinc.com/publications/J_of_Aircraft_1998.pdf provides an interesting ‘operational’ view in the summary; vis:-

“Based on the available meteorological data from research aircraft, it appears that only the most vigorous thunderstorms. i.e. super cells and complexes of thunderstorms, are associated with anvils that contain IWC (Ice Water Content) > 1 gm m^3 in regions outside of the main core of the storm.
There is currently insufficient data to determine the threshold concentration of IWC that will induce rollback. Based on the fact that literally billions of hours have been logged by commercial turbofan engines in common cirrus and anvils, with IWC typically <-0.2 gm m^3 it would appear that these clouds do not contain sufficient IWC to cause rollback problems.
Also, it appears that rollback may be more likely to occur the longer the engines are exposed to relatively high mass concentrations of ice particles and snow at very cold temperatures.
If indeed the TAT temperature rise and associated power loss reported in 1974 was an incipient rollback, it should be noted that this is the only reported incident of this kind associated with a Boeing 747, and this could possibly be a result of the large extent of high concentrations of IWC in the anvil remnants of Tropical Storm Kerry.

While we are not in a position to make recommendations to pilots, we can concur that the standard practice (see FAA Circular 00-24B) of avoiding the regions of high radar reflectivity by at least 20 nm is advisable. In terms of rollback avoidance, the main reason to remain as far as possible from the region of high radar reflectivity is that measurements show that the IWC typically drops off sharply as a function of distance from the storm center. Also, any regions containing convection, i.e. rising cloud parcels or overshooting tops could contain super cooled liquid water, which may exacerbate the rollback problem.
Lastly, the probability of rollback incidents appears to increase with duration in areas of relatively high IWC, so that minimizing the time of encounter in these thunderstorm anvil regions may be advisable.”

The more recent Boeing position (www.sae.org/events/icing/presentations/2007sopenmason.pdf), particularly slide 6, links the 100 (plus) Large Transport Engine events to ice crystals.
IMHO this presentation answers the originating questions.

Note that engine manufacturers do not sit back without action; - General Electric Company (GE) CF6- 80C2A5F Turbofan (http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgAD.nsf/0/2C785B3661CD49F5862573710053ADCE?OpenDocument) A300, but also 747/767 if applicable.
Whilst there may not be specific advice in airframe manuals because defensive measures are already in place, this should not be taken to mean that a problem cannot be encountered.
We all require continued professional enquiry into atmospheric threats, particularly where we might not know how close to the edge of a safe boundary we are currently operating, e.g. a small change in operating procedures for air bleed during the cruise – driven by economics, might cross an ‘icing’ boundary.

In many BAe146 rollback incidents, the FDR showed that crews were unaware of other incipient events; a single engine event was often a multiple event. So in the larger engines with more tolerance to such conditions crews might encounter ice crystals and accrete ice, but due to the different concentration or duration of encounter they do not suffer visible symptoms.

The latter might be theory – possibly just speculation, but it is something that I wish to bear in mind when flying in such conditions.

[punkalouver]

It happens so seldom that the large majority of the pilots can justifiably say: "It never happened to me." Saying that it doesn't happen at all is somewhat untrue.


Similar to the refusal to believe by some on the proper way to operate modern de-ice boots.

Or just the belief that if it doesn't affect any of the types at my airline, it does not exist.

Well look at this....

Regulations.gov (http://www.regulations.gov/fdmspublic/component/main?main=DocketDetail&d=FAA-2008-0402)

"The FAA proposes to adopt a new airworthiness directive (AD)
for certain Boeing Model 747 airplanes and Model 767 airplanes. This
proposed AD would require revising the airplane flight manual to advise
the flightcrew to use certain procedures during descent in certain
icing conditions. This proposed AD results from reports of several in-
flight engine flameouts, including multiple dual engine flameout events
and one total power loss event, in ice-crystal icing conditions. We are
proposing this AD to ensure that the flightcrew has the proper
procedures to follow in certain icing conditions. These certain icing
conditions could cause a multiple engine flameout during flight without
the ability of the engines to be relit, and consequent forced landing
of the airplane."

"The requirement to activate the engine anti-ice prior to descent in
visible moisture with total air temperature less than 10 [deg]Celsius
(C) and greater than -40 [deg]C already exists for airplanes that are
not equipped with a primary in-flight ice detection system, which is
designed to automatically activate wing anti-ice and engine anti-ice
when the airplane is in icing conditions. However, the primary in-
flight ice detection system does not detect ice-crystal icing;
therefore, the engine anti-ice would not be activated during these
icing encounters. There is no requirement to activate engine anti-ice
at temperatures below -40 [deg]C, and this proposed AD would require
activation of engine anti-ice at temperatures below -40 [deg]C.
This condition, if not corrected, could result in a multiple engine
flameout during flight without the ability of the engines to be relit,
and consequent forced landing of the airplane."

So if by chance the 747's operated by Rainboe have CF6 engines, he will be doing what the revised manuals will tell him to do even if he still refuses to believe what many manufacturers, regulators and investigative agencies already know. I suppose if BA has different engines, then this problem is still just an unsubstantiated theory and does not exist.:rolleyes:

[shortfuel]

Well spotted :ok:

[Basil]

I'm out of the business now but little question for someone who understands core icing intimately - if such exists:
What effect does switching on engine anticing have on ice crystal icing?

[Genghis the Engineer]

I don't think that engine anti-icing is likely to have much effect, because that is primarily targetted at ice formation on intakes, not solid ice particles going through the compressor.

Rainboe does make some valid points in that at the moment there is limited knowledge and that a lot of what's there is in research papers, not aircraft manuals - so at the moment sticking to published operating advice is definitely the safest thing to do. That said, those research papers have been prepared by some world-class researchers and subjected to peer review of other world-class researchers before being published, so they are a heck of a lot more than guesswork.

It's clear (for example from the work by Walter Strapp and others quoted by SafetyPee) that there's an issue - hence the FAA/NASA research action that's ongoing. The issue is that *some* rollbacks have happened - albeit 100 in 10+ years is such a rate that most pilots have never knowingly seen it. It's a much smaller issue than conventional icing, if it wasn't we'd all know much more about it. But, I for one am morally entirely behind the researchers trying to understand this better because 100+ rollbacks in a finite period is still a lot, and with enough more there's a risk of an aircraft being lost eventually. That justifies the effort of researching it, and I'd anticipate the subject eventually finding it's way into affected MoMs (starting presumably with those listed by Punka Louvre) and the ATPL syllabus - although I'd guess not for a few years yet whilst the icing boffins try to understand it a lot more (and no doubt publish a fair number more papers!)

G

[punkalouver]

What effect does switching on engine anticing have on ice crystal icing?

According to the proposed AD:

These
conditions can cause ice crystals to
accumulate in the core flow path of the
engine during low-power conditions,
such as idle or idle descent. The
accumulated ice sheds during throttle
increase and is ingested into the engine,
causing the combustor to flameout
resulting in an in-flight flameout and
potential damage to the high pressure
compressor due to ice impact. The GE
CF6–80C2 and CF6–80A series engines
models have similar compressor
designs.
Activating the engine anti-ice
increases the flameout margin and
reduces the potential for multiple
engine flameouts by increasing bleed
flow and idle speed. Engine anti-ice also
assists with relighting the engines by
turning on the igniters on airplanes that
are not equipped with autorelight.
However, in several of the subject
engine flameout events, the engine antiice
was already on when the engines
flamed out. In each flameout event, the
engines relit and continued to operate
normally for the remainder of the flight.

[safetypee]

Genghis, et al; some aircraft have a combined engine intake lip and first stage compressor anti icing system. The146 is an example; the weakness of the compressor element contributed to the ice crystal problem.
The anti ice OFF situation was considered. In ‘theory’, the ice would bounce off an unheated blade / stator and proceed to the ‘hotter’ parts of the engine without problem. However, in this, there are at least two considerations. First, that the air entering the engine and compressor is heated by ‘intake’ compression and thus the first stages could still accumulate ice – note that some engines suffer fan blade icing in similar conditions. Second that in other circumstances not far removed from ice crystal conditions, the IWC of the atmosphere became liquid (and/or super cooled) before entering the engine, again leading to the possibility of icing. The research suggested that an altitude change of 2000 ft below the ice crystal layer might be sufficient to cause this – a change from an unknown problem to a known problem, but each requiring different anti-ice system selections and the crew not having sufficient information to decide which.
Thus for the 146 there was a need to need to fix the root cause - modify the engines; then follow the manufacturers procedures – use anti icing.

The absence of specific procedures/advice in other aircraft (IIRC the 146 has none) may reflect that other manufacturers heeded the research information and modified their engines (search for ADs), particularly those with evolving designs. Manufacturers still rely on ‘airmanship’ for the avoidance of Cbs by a sufficient margin – but what is ‘sufficient’.

Note that the 100+ events appear to be on Boeing aircraft only; I don’t have figures for any others except that the 146 had 50+ and that engine manufacturer’s shared data of events was a very (disturbingly) large file. Obviously, this excluded non-reported or misidentified events, and any that were incipient, ‘close to the edge’ and not seen by the crew.

Perhaps of interest a ‘what if’ question was asked about the use of airframe anti-icing in ice crystal conditions. Did the ice melt, runback, and refreeze in a more hazardous position. At that time, there was insufficient evidence for any practical operational conclusion.

[punkalouver]

Actually Beechjet and Airbus incidents have been mentioned on this thread.

Hmmmm.....Rainboe mysteriously disappeared from this thread. What a surprise.:{:{:{

[galaxy flyer]

The RR BR710 engine on GLEX, G500/550 and B717 have had several ice crystal incidents. I cannot say for the B717, but some have occurred above FL410. The engine rolls back while under FADEC EPR control, presumably ice crystal icing on the EPR probe. The advised solution is to switch to N1 control.

When I was at Eastern we had a B727 at FL330 enter clouds when the TAT indicated no potential for icing and promptly all three rolled back to a near-idle condition. They managed to restart them, but the company advised crews operating in tropical conditions to not hesitate to turn on engine anti-icing even if not strictly called for.

While I understand Rainboe's point of view, we should be open to the fact that the atmosphere holds a lot of surprises that, perhaps, only the dead know for sure. Just because the information is in technical publications and hasn't made it into flight publications, isn't to dismiss it. OTOH, we shouldn't be making up procedures in the cockpit, but where is the harm in using engine anti-icing when under these conditions?

GF