Engine icing problems on 747-8 and 787.
Usual disclaimers apply!
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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).
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.
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.
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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.
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.
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.
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.
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
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.
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
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.
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.
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.
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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.
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.
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a mixed metaphoric (ash and ye shall receive)
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.....
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.....
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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.
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.
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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?
From what I can see, many of the Asian carriers seem to be using GE?
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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
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.
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?
From what I can see, many of the Asian carriers seem to be using GE?
A330 ENGINE CHOICE
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Triple spool v Twin spool
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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?
They redesigned the fuel/oil heat exchanger.
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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
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
It is specific to the 747-8, and there are like 2 in operation!
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?
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
