Engine icing problems on 747-8 and 787.

[Mark in CA]

Boeing warns of engine icing risk on 747-8s, Dreamliners (http://news.yahoo.com/boeing-ge-notify-airlines-engine-icing-risk-747-094401072--sector.html)

TOKYO (Reuters) - Boeing and General Electric have notified airlines about engine icing risk on 747-8 airplanes and 787 Dreamliners with some GE engines, urging carries to avoid flying them near thunderstorms, a Boeing official said.

The issue affects 15 airlines, including Lufthansa , United Airlines, an arm of United Continental , Japan Airlines and Cathay Pacific Airlines .

[rotornut]

BBC News - Boeing: 15 airlines warned over high-altitude ice (http://www.bbc.co.uk/news/business-25068222)

[freshgasflow]

Fifteen airlines have been warned about the risk of ice forming on Boeing's new 747-8 and 787 Dreamliner planes.

The issue - affecting some types of engines made by General Electric when planes fly near high-level thunderstorms - prompted Japan Airlines to cancel two international routes.

There have been six incidents since April when aircraft powered by GE engines lost power at high altitude.

[beamender99]

http://www.pprune.org/tech-log/528432-boeing-ge-notify-airlines-about-engine-icing-risk-747-8-dreamliners.html

[underfire]

Japan Airlines said on Saturday it will replace Dreamliners on its Tokyo-Delhi and Tokyo-Singapore flights with other types of aircraft while also dropping a plan to use 787s for its Tokyo-Sydney route from December.

[fleigle]

It would be nice if future posts on this topic could get into informed speculative, or knowledgeable discussion, about why this high altitude icing is affecting only the GE engines and not the Rollers, just for once, please?.

[Heathrow Harry]

BBC News - Boeing: 15 airlines warned over high-altitude ice (http://www.bbc.co.uk/news/business-25068222)



Fifteen airlines have been warned about the risk of ice forming on Boeing's new 747-8 and 787 Dreamliner planes.


The issue - affecting some types of engines made by General Electric when planes fly near high-level thunderstorms - prompted Japan Airlines to cancel two international routes.


There have been six incidents since April when aircraft powered by GE engines lost power at high altitude.


The Boeing 747-8 series and the new 787 Dreamliner and the only types of aircraft affected by the high-altitude icing issue.

The new warning was given to airlines including Lufthansa, United Airlines and Japan Airlines.



It says aircraft with the affected engines - GE's GEnx - must not be flown within 50 nautical miles of thunderstorms that may contain ice crystals.
As a result, Japan Airlines (JAL) has decided to withdraw Dreamliners from service on the Tokyo-Delhi and Tokyo-Singapore routes.



"Boeing and JAL share a commitment to the safety of passengers and crews on board our airplanes. We respect JAL's decision to suspend some 787 services on specific routes," a Boeing spokesman said, according to Reuters news agency.


A GE spokesman told the agency the aviation industry was experiencing "a growing number of ice-crystal icing encounters in recent years as the population of large commercial airliners has grown, particularly in tropical regions of the world".


He said GE and Boeing were hoping to eliminate the problem by modifying the engine control system software.

[lomapaseo]

Er, isn't it a bit late in the development cycle of an engine to discover this sort of problem?

Engines and airacrft are not developed at the far ends of an icing envelop. Now that it is realized that the operation intends to use this envelop as often as they do, the engine needs to have a work-around for such an encounter.

Lots of other examples in-service where recommendations were not followed to avoid encounters and where extraordinary action need be taken at the product level

[Radix]

............

[TacomaSailor]

The New York Times article says:

"The move came after six incidents from April to November involving five 747-8s and one 787 in which aircraft powered by GE’s GEnx engines suffered temporary loss of thrust while flying at high altitude."

So why isn't the title about the 747-8 problem? - 83% of the reported problems are 747-8 incidents

[phiggsbroadband]

Hi, just seen an announcement that the engines fitted to some Japanese Dreamliners should not be flown within 50 miles of icing conditions...

BBC News - Boeing: 15 airlines warned over high-altitude ice (http://www.bbc.co.uk/news/business-25068222)

Maybe a quick swap of engines is all that is required.

[bvcu]

this problem has been recognised for a while and has given problems on other engines at various times and sometimes causing damage. Must be more serious if this restriction has been mandated.

[lomapaseo]

Lots of possibilities but the effect of this type of icing on one engine model vs another.

If it's mechanical damage then the exact location of the ice buildup and the delay time to shed may produce damage to some blading downstream. The ice buidlup location more often than not is on the probes inside the engine that feed the FAEC etc.

If it isn't permanent damage to the blading downstream, than the effect on the engine cycle might be as simple as a probe blockage and stall condition which is not programed into the recovery logic of the engine FADECs.

Perhaps somebody with knowlege of the fix can interpret what's unique about the specific engine design or recovery logic in these state of the art GE engines

[HazelNuts39]

Atmospheric conditions on intercontinental routes are well known.The problem is that the precise conditions that cause engine power loss (or pitot blockage) are not well known and understood.

[barit1]

NOT addressing the specific present icing condition -

One early turbofan (70s) had stall/surge problems in early revenue svc, associated with heavy rain. The factory had difficulty replicating the condition and the problem.

More field research brought forth the news the engine ran fine within the heavy rain, but when the a/c exited the rain the stall would occur.

So the test rig was modified to turn the H2O on and off very rapidly. Voila! the problem was now replicated!

Turns out the issue was the rapid air temperature change at the LPC discharge was the culprit; water in the LPC flowpath cooled that flow a lot, so the air temperature sensor at that point needed the be a faster-responding design to convey correct data to the engine control.

The water-ingestion tests during FAA certification were not aggressive enough!

[mickyman]

Boeing has warned airlines to avoid flying some Dreamliner planes near high-level thunderstorms due to a risk of engine icing problems.
The warning applies to 15 carriers who have 747-8 and 787 Dreamliners with engines made by General Electric (GE).
It is the latest alert for an aircraft which has suffered a number of technical glitches since its launch, including overheating lithium-ion battery systems that caused the planes to be grounded worldwide for three months earlier this year.
The engine warning follows six incidents between April and November involving five 747-8s and one 787, all of which suffered temporary loss of thrust while flying at high altitude.
The problem was caused by a build-up of ice crystals, initially just behind the front fan, which ran through the engine, a GE spokesman said.
All of the aircraft landed at their planned destinations safely, he added.
Boeing has prohibited the affected aircraft from flying at high attitude within 50 nautical miles of thunderstorms that may contain ice crystals.
In response, Japan Airlines (JAL) pulled 787 Dreamliners from two international routes.
Other affected airlines include Lufthansa, United Airlines, an arm of United Continental Holdings and Cathay Pacific Airlines.
A spokesman for Boeing said: "Boeing and JAL share a commitment to the safety of passengers and crews on board our airplanes. We respect JAL's decision to suspend some 787 service on specific routes."
JAL said it will replace Dreamliners on its Tokyo-Delhi and Tokyo-Singapore flights with other types of aircraft.
It also dropped plans to introduce 787s to its Tokyo-Sydney route from December.
The company will continue to fly the aircraft on other international and domestic routes, which are unlikely to be affected by cumulonimbus clouds for the time being.
A spokesman for GE, which is working with Boeing on software modifications to the engine control system in a bid to eliminate the problems, said: "The aviation industry is experiencing a growing number of ice-crystal icing encounters in recent years as the population of large commercial airliners has grown, particularly in tropical regions of the world."
All 747-8s are powered by GE's GEnx engines, while 787s are powered either by GE units or the rival Trent 1000 made by Rolls-Royce.

Taken from Sky News website.

[Intruder]

Already being discussed in Tech Log:

http://www.pprune.org/tech-log/528447-engine-icing-problems-747-8-787-a.html

[tdracer]

Hazelnuts basically nailed it. The problem with Ice Crystal Icing (ICI) is that it's a relatively new phenomena and is poorly understood.
The FAA regulations don't even account for high altitude icing - I understand that EASA has an engine level regulation that's applicable, but I don't think anyone really knows how to show if they comply.http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/puppy_dog_eyes.gif

I've been "involved" in ICI issues for the last 10 years but I'm far from an expert (I probably know just enough to be dangerous http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gif ) but the threat is something like this:
Conventional icing involves super-cooled liquid hitting cold aircraft surfaces and freezing. Commercial jetliners have typically addressed this threat by heating the threatened surfaces. Conventional icing was not much of threat to the core of the engine because the surfaces were already warm.
Ice Crystal Icing is fundamentally different - it occurs where it is far too cold for super cooled liquid to exist. The ice crystals are extremely small and extremely cold. When they hit the typical cold aircraft surfaces they just bounce off (pilot reports often refer to 'rain on the windscreen' despite TAT way below freezing). However ice crystals in the core of the engine sometimes accumulate and freeze in areas of the engine that are normally far too warm for ice to form (as in 80+deg F/25+deg C). As I understand it (again, I'm not the expert http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/sowee.gif), the ice hits the warm surface, melts, then additional ice hits and cools the liquid water enough for it to refreeze.

When this ice sheds, it can quench the flame and/or cause impact damage to the compressor.

So far, we've seen ICI flameouts on the CF6-80C2, CF6-80E, PW2000, and the GEnx. The circumstances vary between the various engines (CF6 typically ices up during an idle descent, then a shed/flameout results during the accel for a level-off).

The first few GEnx-2B events resulted in short term rollbacks where the ice quenched the flame, but auto-relight got the fire back before the engine went sub-idle. However in the last couple events, there was also compressor damage, which is what got the regulators so excited. None of the affected engines (to date) have gone sub idle before they recovered, so technically they were not in-flight shutdowns, but with compressor damage there is a real threat of a common mode multiple engine power loss.

The current plan is to mitigate the risk with a software change that will open the bleed valves during ICI to dump enough of the ice overboard to prevent a problem. Time will tell if it's enough :rolleyes:. A large part of the problem is that the conditions are nearly impossible to re-create on the ground (among other things they can't generate ice crystals that small). And even in the convective weather systems that can result in ICI issues, the actual conditions that adversely affect the engines are rare.

While it's true most of the events to date have been the GEnx-2B on the 747-8, the -2B engine has way more operational hours than the -1B on the 787. Since the -1B has also had an event, there is no reason to believe it's fundamentally different.

Now, as to why GEnx engines seem to have a problem and not RR Trent? Figure that one out and I'm sure GE has a fat paycheck waiting for youhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

[WHBM]

Sounds not dissimilar to the issues with the old Bristol Britannia large turboprop in the 1950s, which had engine icing issues near tropical thunderclouds that badly impacted its development. Although mainly ameliorated, it was never completely overcome in the lifetime of the engine/powerplant, and crews developed their own procedures for it. Maybe there are a few old Britannia flight engineers still around to advise GE !

[JW411]

Or the roll-back phenomena that affected the ALF 502 engine on the BAe146 which left two aircraft gliding with all four shut down. Fortunately, on both occasions the crews managed to retrieve the situation. One of them got down to 2,500 feet (luckily out to sea) before they got a successful relight.

[gas path]

Not only the GenX but the GE90 suffers too. The stage 1 hpc can get quite severely bent blades from ice crystal formation that collects on the pt25 sensor breaks off an puts a nasty bend in the blade(s).

[fleigle]

TDRACER
Thank you for that informative post, more please.
:ok:

[lomapaseo]

Not all engine ice releated issues are due to ice crystals at high altitude. Many are due to low power on the ground or flight idle, building up ice in the LPC and then later shedding into the HPC stage 1 blades (spinning much faster). The consequences of these bent blade may not be felt until sometime later in the flight where the engine compressor surge margin is impacted.

Many engines in some fleets even go for a long time with such damaged blades and are found only during overhaul in a shop.

Of course unlight problems are felt to be instantaneous to a shed.

Like I said earlier, the engine response is predicated on the Fadec logic and bleed locations to recover from rare events. That and where the probes are located sets the difference between engine models as well as the time spent poking around the sky in the vicinity of ice crystals.

I suspect that both Boeing and Airbus are going to spend more effort at defining their intended icing envelopes so as to ensure that their purchase specs on the engine aim at recovery tolerance shoud they find themselves in an icing environment not covered in the certification specs.

This is neither a Boeing nor a GE problem, it's and industry problem and need be addressed outside the scope of the current engine certification regulations for the ttime being.

[Nemrytter]

A large part of the problem is that the conditions are nearly impossible to re-create on the ground (among other things they can't generate ice crystals that small).Is that an issue to do with generating the sheer number of crystals required? It's quite easy to generate these small crystals in the lab, but I'm unsure how it'd scale up to the number density required for flow through an engine.
And even in the convective weather systems that can result in ICI issues, the actual conditions that adversely affect the engines are rare.This is debatable, in my view :)
These HAIC seem to form much more frequently than was originally thought, but mainly in areas where there are relatively few flights (tropical Africa and equatorial Atlantic from my work, not sure about the other size of the globe). Something that interests me is why North America, despite having many large convective storms, doesn't seem to be affected by this ice so much - we rarely see it there. I guess the other important question is just how much of this stuff we need in the air before it starts causing problems.

[safetypee]

Generating crystals on the ground. One engine test centre likened this to having to generate a CB in an engine test cell. High levels of ice/water content (4mm/m^3), subfreezing conditions (requires liquid nitrogen), low air pressure, and the correct mass/airflow through the engine running at cruise conditions with ice protection on.

Research / test flying several years ago, only managed one engine malfunction in 20 plus flights over a two year period. This work identified aspects of the high levels of ice water content, the duration of exposure (cross anvil vs long duration in the cloud mass) and a myriad of varying engine conditions. This was further complicated by large areas of CB uplift and the difficulty in detecting the conditions with WXR. Also, these conditions could be found in temperate latitudes.
Thus there may have been many encounters, but only a few resulted in observable problems.
50nm is a reasonable margin assuming that the errant CB can be identified; and not to forget that the hazard is a multiple engine event not just the failure of one.

Why now: modern engines are built to much finer tolerances – supercritical designs (cf the stall problems due to squashed flies on an aircraft supercritical wing section). Also the fine running margin to be maintained by FADEC; older designs would cough and spit the ice out, new designs are relatively more fragile.
Also, consider that as WXR capabilities advance, do we fly a little bit closer to CBs because we can see them; but where is the ice, the anvil, etc.

[tdracer]

In the aftermath of the TACA 737-300 dual engine failure in 1988 (emergency landing on a levee), a great deal of work was done regarding 'conventional' inclement weather threats to jet engines. Things like inward opening bleed doors (did a better job of scooping ice and water out of the flow path), and even subtle changes to the shape of the spinner would help direct ice and rain away from the inlet to the engine core have been implemented. Special 'icing tunnels' have been developed to simulate the threats and devise necessary improvement. As a result, the engines that have been introduced since then have demonstrated very good behavior in 'conventional' inclement weather.

At the same time, the rate of Ice Crystal Icing events has increased dramatically. There is plenty of debate as to why - global warming/climate change, more flights into the threat, or is there something about the newer generation of engines that makes them more susceptible (I suspect it's a combination of all three).

For a long time, most of the ICI events occurred in the South Pacific/Pacific Rim area, but that's been less the case the last 10 years, with a number of events occurring over the Americas.

Nemrytter, as I previously noted I'm not an expert, but when we did some Ice Crystal testing on a CF6 several years back, I believe they simply used large blocks of ice, with some sort of device that shaved off ice crystal material - the technique was heavily criticized at the time as not being representative, but no one had good suggestions as to how to make it better http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/confused.gif

Gaspath - The GE90-94B has indeed suffered compressor damage, but to date there have been no reported power loss or flameout events. Interestingly, there have been no reports of compressor damage on the GE90-115B, but I don't think anyone really understands what the difference is.

The PW2000 was in service for over 20 years before they had an event - then Northwest/Delta started basing a few 757s our of Narita, and sure enough within months they had an event (flameout at cruise) - in that South Pacific region which used to dominate the reports - and there have been a few more PW2000 events since then.

The GEnx events to date have all occurred at very high altitude - between 37k and 41k - and all at cruise. Very different from what we've seen on the CF6 that mainly have occurred during a descent at/near idle.

Nearly all the events have occurred either in the equatorial regions, or during the summer months in that hemisphere.
There have been a number of proposals to take a flying test bed type aircraft with heavily instrumented engines and go looking for ICI. Until recently those proposals have not gotten very far, but with the recent GEnx events that may change.

[tdracer]

safetypee, you made your post while I was writing mine - in short I pretty much agree.


One detail, ice crystals themselves do not show well on weather radar - to avoid they need to look down for the convective weather below them that's causing the IC threat rather than looking for the crystals directly.

[Turbine D]

tdracer

Good posts!
A couple of added things:

In the recent past, 60% of engine rollbacks or flameouts at high altitudes occur in the Asia-Pacific region, probably because of the propensity of deep updraft convective buildups on the number of airliner routes flown over tropical water in that part of the world. Most occur at cruise or during initial descent. It is now believed that localized areas of high ice crystal density have up to 8 grams per cubic meter of ice crystals or water content whereas the current engine design standard for super cooled liquid water has only 2 grams per cubic meter.

Originally the problem of high bypass turbofan powered large transports at high altitudes between 35K - 41K feet was thought to be relatively the same as encountered by turbofan powered commuter aircraft that generally flew at lower altitudes between 28K - 31K feet altitudes around major thunderstorms. The commuter aircraft fly through clouds at high continuous thrust settings and noticeable moisture in the form of water or ice. However, convective buildups are different over land where most commuter aircraft fly verses deep updraft convective buildups over tropical waters that are supplied continuous water through the updraft cores. These deep draft convective buildups are dominated by ice particles and have little in the way of supercooled LWC (liquid water content).

For the GEnx engines, the solution, tracer pointed out, to end the rollback or flameouts is by opening the bleed valves, it should work so long as the location of ice accretion is not in the HPC beyond any bleed valve points.

It should be noted, that earlier this year for the first time, NASA Glen researchers were able to re-create the high altitude ice crystal cloud environment in the propulsion testing lab during a full scale engine test that resulted in loss of engine power. Although the shape of the ice crystals can't be varied, this is the first step to give the industry a new tool in design, testing and certification of turbofan engines relative to the ice crystal phenomena.

[TheShadow]

So what happens if you encounter ice crystals whilst within a volcanic ash cloud?
Wouldst be a good thing or a bad thing?
Lots of condensation nuclei inside those thinly concentrated ash clouds that float on in the stratosphere well after an eruption .....might serve to encourage ice crystal formation. But with some added water in the form of melting ice crystals it might just give you a good blade polish (Like throwing a bucket of walnut shells down the intake).

withdraws tongue from battered cheek.....

[underfire]

Shadow,

Luckily, if ice formed on the ash, it would precipitate...

On the ice formation, while there are many 'fixes' the root cause needs to be identified.

In my opinion, for whatever that is worth, I would look at the compression around the cowling, there must be an issue that locally reduces pressure and allows the icing formation.

[acutabove007]

Now not knowing many of the technicalities of the two (or more?) engine options for the 787 (General Electric GenX/RR Trent 1000) but having a huge interest in turbine engines, could someone explain to me why certain airlines would choose one and not the other, or is it just the obvious thing being financial, or is one better for different roles and environments then then the other?

From what I can see, many of the Asian carriers seem to be using GE?

[Radix]

............

[Nemrytter]

Nemrytter, as I previously noted I'm not an expert, but when we did some Ice Crystal testing on a CF6 several years back, I believe they simply used large blocks of ice, with some sort of device that shaved off ice crystal material - the technique was heavily criticized at the time as not being representative, but no one had good suggestions as to how to make it better Wow, it definitely isn't representative! As you say though, better than everyone else's (non-existent) suggestions.
One detail, ice crystals themselves do not show well on weather radar - to avoid they need to look down for the convective weather below them that's causing the IC threat rather than looking for the crystals directly.
The other problem is that they can often drift quite a long way from the area that does show up on radar. Off the top of my head we've seen them in satellite data up to around 60km away from the area that would produce strong radar returns. Hence Boeing's 50nm advice, I'd imagine.

[TURIN]

Now not knowing many of the technicalities of the two (or more?) engine options for the 787 (General Electric GenX/RR Trent 1000) but having a huge interest in turbine engines, could someone explain to me why certain airlines would choose one and not the other, or is it just the obvious thing being financial, or is one better for different roles and environments then then the other?

From what I can see, many of the Asian carriers seem to be using GE?

Some discussion here re engine choice-not 787 though.

A330 ENGINE CHOICE (http://www.pprune.org/tech-log/502186-airbus-330-engine-ge-cf6-trent700-pw4000.html)

However, if you want to join the handbags at dawn brigade....

Triple spool v Twin spool (http://www.pprune.org/tech-log/444991-american-twins-brit-triple-spool-engines.html)

Enjoy. :ok:

[underfire]

Why is the 747 not withdrawn

It is specific to the 747-8, and there are like 2 in operation! :\

[mary meagher]

So this has no relation whatsoever to the 777 approach to LHR when the RR engines had a problem answering the throttle at a critical moment due to ice melt? How did RR sort that problem?

[TURIN]

They redesigned the fuel/oil heat exchanger.

[acutabove007]

There was a very good "air crash investigations/seconds from disaster (or similar)" on what happened and how the only logical option left was ice.

If I remember correctly, and perhaps someone with more knowledge could correct where im wrong, the heat exchangers tubes where the fuel would run through protruded out of the cylindrical container only by a couple of CM (if that) and due to the fact that the oil only really heats the parts of the tubes that it touches or that are in close proximity through conduction, passing almost waxed fuel through at -40 degrees C or or close, the protruding parts of the tube that stuck out one end, were not heated enough, and therefore when the FO disengaged the Auto Throttles, and added power, a flow of frozen fuel rushed through towards the tips of these pipes and physically blocked them, starving the engines of fuel..and well we all know what happened next.

I believe the fix was fairly straight forward, as they shortened the pipes so that nothing protrude and so that it was all properly heated.

It was a 777-200 ER G-YMMM which I thought had RR Trent 800 as opposed to the 300 ER which has the wonderful GE90 Powerplant

Sorry I cant find a link to the investigation, but I would recomend you look it up as its very interesting to see the mock up of the system they recreate

[tdracer]

It is specific to the 747-8, and there are like 2 in operation!

Underfire, there are over 50 delivered (a few -8I are are in mod centers getting VIP interiors so I'm not sure the exact number in-service), and ~ 250,000 flight hours since EIS. A couple times as many engine operating hours as GEnx 787:*

[tdracer]

So this has no relation whatsoever to the 777 approach to LHR when the RR engines had a problem answering the throttle at a critical moment due to ice melt? How did RR sort that problem? As others have noted, totally unrelated - the BA 777 occurred when what is referred to as 'sticky ice' (seriously, it's in the FAA training materials now) obstructed the Fuel/Oil Heat eXchanger. The FOHX was redesigned in the aftermath - acutabove is correct that they changed the way the small tubes entered the heat exchanger to discourage ice formation in that area, but the most important change was the addition of a bypass to the FOHX - if the delta pressure gets above some level (memory says ~30 psi) the bypass will open and allow the fuel to the engine.

The TV show I saw (I think it's called 'Terror in the Sky's' - it's on the Smithsonian channel in the US) got it about 75% right, then totally blew it with two 'facts'. First, they said the engines 'failed' - they didn't fail, they just didn't respond to the throttle command to accel (because the FOHX would only allowing about 4,000 lbs/hr to pass) and were still running above idle when the airplane hit the ground. Second, they showed beautiful pictures of the fuel test rig, and a diagram of the FOHX showing where the ice formed, then referred to the FOHX as the "Fuel Filter" - repeatedly :ugh::ugh::ugh:

[Goat Whisperer]

Does anyone have a link to the original Boeing/FAA/GE advisory? I have tried much engoogling but only GE media reports about said advisory.

[Green Guard]

FAA to warn airlines of engine icing risk on Boeing 747-8s, Dreamliners - Yahoo Finance (http://finance.yahoo.com/news/faa-warn-airlines-engine-icing-risk-boeing-747-025900608--sector.html)

[Steak&Kidney_Pie]

BBC News - Boeing: 15 airlines warned over high-altitude ice (http://www.bbc.co.uk/news/business-25068222)

[Green Guard]

So only engines are affected, right ?
No problem with any other part of aircraft, right?

If so, it has nothing to do with ICING, but with ice crystals filling some sophisticated engine electronic inputs i.e. "Bill Gates' Windows" probes...
All other aircraft including these will not lose power due to ice crystals but because PT2 or whatever is called tube if not properly heated and filled with ice crystals will give false indication to engine control or EPR etc... but will not affect engine power, unless Auto Throttle is on.

PS
Flying 50 or even 555 NM clear of CB will not solve the problem. Any stratus cloud or any cloud at all, may contain those crystals on high altitudes.


:suspect:

[Nemrytter]

Do you mean cirrostratus clouds? Plain old stratus clouds are low altitude and composed of water - they are not an ice crystal hazard. Cirrostratus do contain ice crystals but these are a) Much bigger (by about one order of magnitude) and b) Much less dense (by about 2 orders of magnitude). This means they are nowhere near as big a hazard in terms of ICI than the very dense ice clouds we see being produced near Cbs.
Same with normal cirrus clouds, by the way: They're about an order of magnitude less dense than the Cb associated clouds and (as far as I know) have not been implicated in any rollback events.

[safetypee]

The effect of ice crystals varies with engine type. The hazard involves large quantities of micro ice particles at high altitude. The previously quoted water/ice densities are like a heavy rain storm at ground level (a strong umbrella required), but with ice crystals there are additional criteria such as density, heat-flow, and ‘stickiness’.

In some engines, the heat flow of the compressor intake-anti icing (inside the engine) might be overwhelmed by the ice mass flow and heat loss. Or more likely result in partial melting enabling the ‘cold’ water to act as a glue to stick ice crystals together (run back ice), resulting in a rapid build-up which chokes the first stages of the compressor (cf pitot problems). The associated changes in air flow may be sensed by the fuel control system which reduces the fuel flow, which results in a reduction in engine speed, which affects the rate of ice build-up – and thence a continuing cycle resulting in ‘rollback’ to idle/sub idle. There may be a point at low rpm where fuel is added (to maintain idle) by the FCU or manual, but the engine is unable to respond and thus the additional fuel increases the engine temp resulting in a further control cycle with a risk of over-temp / stall / shutdown.

Engines may also suffer from ice lumps breaking off with potential damage to later stages of the compressor; and which can affect engine performance after an encounter – even if not detected at the time.
Different engine designs with slightly higher anti-ice heat-flow may protect them in most conditions; similarly an extended compressor intake lip may centrifuge the ‘relatively’ denser crystals (or a significant proportions of them) away from the compressor and exit harmlessly through the fan duct due to fan-whirl – spinner shape, fan design, by-pass duct shape, size, speed, etc.
All of these variables also depend on ice density, duration of exposure, ambient and compressor temperatures according to power setting / aircraft speed.

The safety problem is how to anticipate the combinations in a test program and ensure that you flight test in the appropriate conditions, except you don’t know what appropriate means.
Original designs should cope with a wide range of conditions (cert regs), but then there is longer term exposure to the real atmosphere and real flight operations; – in safety you never fight the war that you train for.
Thus modifications might consider changes to hardware, anti-ice heat flow, or fuel control system – air/fuel flow. And temporarily avoiding the most likely conditions, but with associated risk of human judgement of what is most likely (regulation advisory warning), and adherence to procedures (operator).

[Ferpe]

I happen to have the temp versus station diagrams for the GEnx and the T1000 (I analyze engines over at Airliners.net) so I thought I post them here as well, here the link to the Airlines post:

How Does A Software Change Solve Icing Issues? — Tech Ops Forum | Airliners.net (http://www.airliners.net/aviation-forums/tech_ops/read.main/340700/#8)

The diagrams show very clearly why a 2 shaft booster engine can have the type of icing problems discussed and why a 3 shaft is less affected. First the GEnx-1B:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/GEnx-1Btemperaturevsstations20131127_zps7364b80a.jpg

Then the T1000:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T1000temperaturevsstationsannotatedforicing20131127_zpsa0bc2 989.jpg

As said these are the design point diagrams,top of climb in these cases. The cruise temps will be somewhat lower, the ToC thrust is around 17klbf and the typical crusie thrust around 10-12klbf at FL350 and higher.

Now one can see that there is low temps before the HPC in the 2 spool as the booster works with very low pressure rise (less then 1.5 in cruise) and hence temps, the temps might just be enough for the thawing and refreezing cycle discussed. The 3 spool is cold until the IPC comes and then it raises the temp fast as it works with optimal RPMs (the booster spins with the fans low RPM), hence the ICI does not thaw until they thaw completely and don't reattach.

[safetypee]

Re AD 2013-24-01 (#49); another masterpiece from DOT / FAA, but at least they do try :rolleyes:

“…prohibit operation in moderate and severe ICI conditions” This is a very thin safety line particularly where the conditions cannot be detected directly, only by supposition based on WXR defined Cb activity.
And what are moderate to severe ICI conditions vice conventional icing conditions – don’t you have to be in them to know the difference.

The industry has a new hazard; MCS – “a large Mesoscale Convective System … where several thunderstorms have merged, with a continuous cloud larger than 100 kilometers (62 miles) across.”

Events with other aircraft types were not necessarily constrained to “warm geographic locations” or above 30000ft. Also, not all of the likely conditions would be identified by the crew, e.g. as being in cloud, some of the very thin wispy cirrus conditions may not constitute IMC.
Is the industry pushing the safety assumptions a bit far by allowing a dispatch after only three engines have been inspected. Is it more likely that a ‘damaged’ engine will fail at high thrust during takeoff .
What if ICI conditions are encountered and an engine suffers damage without any EICAS alerting?

“ … unrecoverable thrust loss on multiple engines can lead to a forced landing.” There must an award for such a statement.

[Dave Therhino]

Yeah, it's fun to ridicule government employees, isn't it?

The FAA's published requirements were developed jointly with Boeing and GE, and used terminology in the preamble that came from messages Boeing sent to their operators. This is done to be consistent with manufacturer publications whenever possible. The statement about the results of multiple engine power loss is required by policy and by FAA counsel - the AD must state the unsafe condition, even if it's obvious.

In this case there was a lot of discussion to reach agreement on an appropriate limitation because there is no direct way to detect the ice crystal conditions in advance of being in them, and wind is a factor. This was not an easy issue to positively address without potentially creating a large economic impact.

It would be a mistake to assume the FAA engineering staff is incompetent. Just ask Tim (tdracer).

[safetypee]

Dave,
“… it's fun to ridicule government employees, isn't it?” yes, but … “It would be a mistake to assume the FAA engineering staff is incompetent …”. I totally agree, but there are occasions where mild ridicule which refocuses attention might improve the objectives of a safety message.

Undoubtedly this issue is being considered by many parties with great expertise and who have access to more information than is made public, but the quality of these activities is often judged by what is said / published.
DOT/FAA are the custodians of safety and publications – even though the text may be drafted elsewhere; they, at the end of the process, should be expected to ask if what is being conveyed makes sense and will it achieve the objective. Are the explanations and procedures written from their point of view, with their responsibilities for safety in mind, or from the views of operators and the pilots who have to judge and manage the risks in potentially hazardous situations.

Regulatory authorities provide guidance on risks - as to what might be acceptable or not; in simple terms they ‘take a risk’, based on well-judged and proportioned reasoning to maintain the required safety level. However, it is the pilots who ‘run the risks’; theirs’ is the final safety call which often depends on situation assessment, which in this instance requires clear and concise depiction of the conditions and how they can be identified.
This is an onerous task for everyone in the process and warrants careful thought, which from the current public view might have been better considered.

Yes the above is posted with hindsight, but better to consider this hindsight as foresight now, rather than start again after an incident; then the judgement of economic aspects, etc (a fine balance with safety) will be wrong, whereas today, ‘it is right’.

[Capot]

I understand that there is an FAA statement that if there is another occurrence of ICI in GEnx engines the TCs for the 747-8 and 787/GEnx will be withdrawn.

If that's already been posted, apologies; I didn't find it. Is there any corroboration of that information?

[barit1]

another occurrence of ICI in GEnx engines the TCs for the 747-8 and 787/GEnx will be withdrawn

Since the problem has only occurred in a narrowly-defined region of the envelope, it's more appropriate that an AD be issued to avoid that condition.

[alf5071h]

barit1, excepting that the narrowly-defined region is ill-defined and depends on the crew to identify it. In addition, the probability of total power loss in not the usual certification consideration where independent probabilities of engine failure might be used; with ICI it is one single event capable of affecting all engines simultaneously; the failures are not mutually exclusive.
The events so far have not involved all engines. It would be interesting to understand why, which might refute the probability theory. However, 2 engines out on a 747 should be manageable, but 2 out on a 787 … …
If there is another event then the situation and circumstances might be very revealing in many (unfortunate) ways.
It is possible that the justification for the current restriction has considered that most engines recovered power and were not damaged beyond immediate use; however the sample size is very small for an ‘unanticipated’ situation.
The AD is a very fine safety line which depends on human judgement, hence the need for quality advice.

[barit1]

U.S. regulators are poised to order airlines to avoid flying Boeing Co. (BA) 787 Dreamliners and 747-8 jumbo jets with General Electric Co. (GE) engines near thunderstorms after some of the planes experienced ice buildup.

A directive due this week is an 'interim action' to ensure pilots fly clear of icing conditions that could reduce thrust from GEnx engines, the Federal Aviation Administration said yesterday. The U.S. move follows Japan Airlines Co. (9201)' s decision to shift to other jets from 787s on some Asia routes.

The icing risk adds urgency for pilots to steer clear of thunderstorms already shunned because of potentially deadly lightning and turbulence. Jets flying at high altitudes through tropical zones can be at risk from powerful storms that promote the formation of performance-sapping ice, according to GE, the world's largest maker of jet engines.

'It's a relatively rare phenomenon because it requires just the right meteorological conditions, ‘Hans Weber, president of San Diego-based aviation consultant Tecop International Inc., said by telephone. 'This isn't a problem that will be limited to GE engines. These crystals have been found in all engines at high altitudes near thunderstorms.'



JAL, United

The twin-engine Dreamliner, the first jet made chiefly of composite materials, entered service with ANA Holdings Inc. (9202)'s All Nippon Airways in October 2011. Tokyo-based ANA, the biggest Dreamliner operator, uses Rolls-Royce Holdings Plc (RR/) engines on its planes.

JAL's 787s have GEnx engines, as do the Dreamliners flown by United Continental Holdings Inc. (UAL), the only U.S. airline flying 787s. Chicago-based United hasn't changed schedules or routes for its Dreamliners, said Christen David, a spokeswoman.

Atlas Air Worldwide Holdings Inc. (AAWW), the lone U.S. operator of 747-8s, adjusted operations after Boeing's Nov. 23 warning for GEnx-equipped jets to stay 50 nautical miles (93 kilometers) from storms, said Bonnie Rodney, a spokeswoman.

Any disruptions for the freighters from the Purchase, New York-based company 'will be minimal and can be managed with only minor reroutings,' Rodney said yesterday.



Replacement 747-400s

Cathay Pacific Airways Ltd. (293), the Hong Kong-based airline, said it has 10 Boeing 747-8 freighters in its fleet that are powered by GE's GEnx engines. As a precautionary measure, it's standard operating procedure for 747-8 freighters to avoid flying into thunderstorms, Cathay said in an e-mailed response.

The European Aviation Safety Agency has adopted the FAA safety directive, spokesman Dominique Fouda said today.

Deutsche Lufthansa AG (LHA), the largest customer for the 747-8, said that from December the nine jets already delivered will not operate above 30,000 feet or avoid storms. Weather conditions en-route will be closely reviewed and, in some cases, other aircraft such as 747-400s equipped with other engines will be used, Lufthansa said by e-mail.

'This looks a lot like a classic teething issue,' Richard Aboulafia, an aerospace analyst at Fairfax, Virginia-based consultant Teal Group, said by e-mail. 'It's probably isolated to just the engine, and even then just one of the two engines available as options. It's also probably easily fixed with a software tweak, rather than any kind of hardware modification.'



Software Modifications

GE said it's making software modifications to eliminate the ice-buildup risk and expects them to be available in the first quarter. Marc Birtel, a spokesman for Chicago-based Boeing, said the engines' design and maintenance practices, together with the new instructions, allow for the jets' 'continued safe operation.'

'The FAA has been working closely with Boeing and GE to monitor and understand these events as the companies develop a permanent solution,' the FAA said in a statement. It didn't give a specific day for issuing the airworthiness directive on the planes, which only covers U.S. carriers.

Both the 787 and 747-8 have had bumpy debuts. The 747-8 was two years late in starting service in 2011, and slack demand forced Boeing to cut output. The Dreamliner, whose 2011 entry was 3 1/2 years late, was grounded for three months in January after meltdowns in the lithium-ion battery packs on two planes.



Six Cases

Boeing fell 2.2 percent to $133 at the close in New York, while GE declined 1.3 percent to $26.73.

There have been six cases since April of planes with GEnx engines temporarily losing thrust in high-altitude icing conditions, Fairfield, Connecticut-based GE said Nov. 23. Five were with 747-8s and one was with a 787, according to the e-mailed statement.

Japan Air will replace 787 Dreamliners on flights between Tokyo and Delhi with Boeing 777s until Nov. 30, and will switch to 767s on its Tokyo-Singapore route, according to a Nov. 23 statement. The Tokyo-based carrier will make a decision this week on flights past Dec. 1, said Jian Yang, a spokesman.

Boeing surpassed 1,000 orders for the Dreamliner with its haul at the Dubai Air Show this month. The company handed over 57 of the four-engine 747-8s, through the end of last month, most of which are freighters.

'Airlines wouldn't be too concerned about engines in terms of costs,' K. Ajith, a Singapore-based analyst at UOB Kay Hian (UOBK) Pte. 'There will be some of sort compensation for airlines. Despite the problems, the aircraft is quite popular.'