Close to zero chance.

The operators of the aircraft have been aware of these results for some time. So have the FAA. Aircraft rotations and new methods of operation have long since been implemented.

DeScally

The "authorities" do not take the decision to ground aircraft lightly. I would suggest this is not a grounding candidate.

I would expect the operation of the aircraft to be restricted. eg No flight sectors over 10 hours to be undertaken, Cruise altitude reduced in areas of extreme low temperatures etc.

Implementing of any mod action to be done within a time scale of perhaps, say, 24 months?

Quote :

Phil, I beleive it does at least allude to where it came from...

The varied (and higher levels) of water can come from less than homogeneous distribution in the tank, but mainly from prior upstream ice melting, either from the boost pump screens or from pipewrok less far upstream.

As I took it to mean ppm at the point of interest e.g. in the pylon pipework or adjacent main tank pipework.

I believe they also inferred that concentrations could vary wildly from time to time in the fuel passing through the critical pipework sections, up to possibly 125ppm.

.. without of course re-reading or quoting directly.

unquote


I could well be wrong, but I believe that is more a coment on the problems of measuring water content, rather than anything to do with actual water in the accident aircraft. The report does say it expected a lower than maximum water content because of ice forming at the bottom of the fuel tanks, so that the fuel circulating would have a lesser ppm of water. What the comment MAY imply is that the tests on fuel either for ground supply or in aircraft sampling may need examination.

.

Having slept on it, I believe the AAIB interim Report no. 2 is rather odd.

If one believes in a total safety (non-commercial) attitude, then three cheers, but I do feel that the NTSB and FAA have "bounced" the proper authority, the AAIB, still that's the real world.

Just a look at the actual recommendations ;

Safety Recommendation 2009-028
It is recommended that Boeing and Rolls-Royce jointly review the aircraft and engine fuel system design for the Boeing 777, powered by Rolls-Royce Trent 800 engines, to develop changes which prevent ice from causing a restriction to the fuel flow at the fuel oil heat exchanger. (to which was added : ‘Boeing and Rolls-Royce have accepted the above recommendation. To mitigate the potential for a future fuel system ice accumulation and release event, to cause a blockage at the inlet to the FOHE, Rolls-Royce have developed a modification to the FOHE. The modification will improve the FOHE’s capability in the event of a fuel system ice release event.’)



Safety Recommendation 2009-029
It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency consider mandating design changes that are introduced as a result of recommendation 2009-028, developed to prevent ice from causing a restriction to the fuel flow at the fuel oil heat exchanger on Boeing 777 aircraft powered by Rolls-Royce Trent 800 engines



Safety Recommendation 2009-030
It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency conduct a study into the feasibility of expanding the use of anti-ice additives in aviation turbine fuel on civil aircraft.


Safety Recommendation 2009-031
It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency jointly conduct research into ice formation in aviation turbine fuels.



Safety Recommendation 2009-032
It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency jointly conduct research into ice accumulation and subsequent release mechanisms within aircraft and engine fuel systems



All very sensible, but the ones that interest me are numbers 31 and 32.

31 is sensible but a can of worms, it is open ended, but very important and likely to be long and expensive.

32 is the one that really worries me. It is non specific and non-urgent. However, having found potentially worrying new fuel/water/ice inter-actions there seems no worry over testing ALL aircraft/engine installations and establishing new rules for design and operation. VERY ODD. How does anyone know whether their aircraft is prone to this problem ?

.

From the AAIB recent interim report:

And:

It does seem that there is a lot more to learn here that may apply to other types of 777 or even other types of aircraft. It's nice to have a "quick fix" in redesigning the RR FCOC but it may only be fixing part of the problem...

Quick question...

Who will actually fund the rectification of the 777/Trents? How many aircraft are affected?

a) Will this be picked up by the airlines?, or

b) Will it be paid for by Boeing as its a system problem (for which the solution resides in the RR engine), or

c) Will it be paid for by RR for all affected Trents on 777?

d) a share between b) and c)?

I assume Trent 800s that are not on 777s are not affected? If so this suggests it is the installation of this engine in a 777 that precipitates the problem - hence its a system issue, not just down to the engine (I assume Boeing are the DA for the complete fuel system).

Thoughts?

PS The research proposed in the post above #31/32 is appropriate - you'd first try and properly understand the issue by studying the basic mechanisms for icing, then you could relate it to current designs. If you just started by analysing current designs, you could end up learning very little and it would take longer to technically solve and create robust solutions.

I still don't see any analysis of the following :

1. How can the engine design have been in service for 15 years before such incidents happened. What caused it to work fine on comparable flights until now ?

2. What are the specific aspects of the design that cause this to be a problem, which are not present in engines from other manufacturers, or other designs from the same manufacturer ?

3. Is there any relevance that both aircraft involved in the incidents originated at the same airport, and were quite likely refuelled from the same supply system with the same national fuel spec ?

Robust solutions
 

WHBM, re: "same airport". Didn't the BA depart Beijing, and the Delta Shanghai ?

WHBM,
I think you'll find that the BA777 originated from Beijing. Back to the drawing board.:ok:

The issue is the amount of protrusion of the heater matrix tubes above their support plate within the FOHE. These are notoriosly difficult to manufacture and the protrusion height is largely driven by their method of attachment, i.e. brazed joints.

If they protrude above a certain dimension then it is likely that any upstream release of a "snowball" will not pass cleanly through the FOHE and will "stick" or "cling" at the FOHE heater matrix inlet plate and hence restrict fuel flow.

The solution is to provide a bypass within the FOHE, similar to that provided for Fuel Filters, which is where, I believe, RR are heading.

The problem is that the current EASA fuel icing cert requirements do not include testing with fuel at a temperature conducive to "sticky ice", ("Snownballs" or "Sticky Ice" occur in fuel at or around -8°C). However sticky ice does not seem to be an issue if, as above, heater matrix tube protrusion is below a certain value.

ps, according to Today's Telegraph (online) the FOHE is there to cool the fuel................:ugh:

Dr Daniel Hoeltgen from EASA
 

Is this fellow one of our guardians of public safety?

Just heard him talking at length on BBC News. Very sadly for him, because I am sure he considers himself a nice knowledgeable sort of chap, this morning he sounded like a poor example of a spin doctor caught in the beam of someone's headlights, but one paid to spin regardless. NB I said "sounded like".

I think he wanted us to know that an AD was issued long since, which apparently bounds operations in such a way as to keep the gremlins at bay whilst Boeing and RR flush them out.

He also seemed to be wanting us to know that suggestions of grounding were obviously groundless since NTSB and others had not ordered it. I guess that means grounding is off his menu, or we can whistle for it.

I see he talks a lot for EASA (and the following was from an article about Helios but I make no apology for that):

From The International Herald Tribune
By Nicola Clark and Heather Timmons

Wednesday, April 23, 2008:Out of general interest, was there, or has there now been an EASA directive applying in this case? Would EASA be the authority ultimately responsible for any decision on grounding European airline Trent engined 777s?

What proportion of the Trent engine 777 fleet is directly under auspices of EASA?

WHBM

In one of the earlier AAIB preliminary or interim reports, it was stated that this aircraft simultaneously flew through abnormally cold air and unlike other aircraft on the route did not descend due to temperature effects *and* it's engines were operated at unusually low fuel flows and unusually gentle step climbs were performed. It seems that these parameters were right at the lower end of many tens of thousands of 777 operational data records.

Further to this a long continuous (or nearly so) descent occurred, so the first time any significant thrust was needed was as the drag rose when the aircraft was configured for landing.

That is likely to explain why the event was, at the time, unique.

A very interesting point, which we have also been discussing on a closed mailing list. Two possibilities spring to mind:

1- There have been some previous incidents, but all happened at altitude, as with the Delta flight, and were thought to have been non-events, except for a driftdown. They may also have been wrongly attributed to core-icing or other factors.

2- With ETOPS extensions, extended flights over arctic regions, even in the Northern winter, have increased in recent years, leading to a much higher number of flights with very cold fuel.

This has been discussed quite early after the BA 038 accident.

One of the main design differences is that in the Trent design, the fuel first goes through the low pressure pump (this is not the boost pump or override/jettison pump in the tank, but a mechanically driven engine pump), then through the FOHE, and then through the HP:

LP-Pump -> FOHE -> HP pump

In the GE design, the fuel first goes through the LP and HP pumps, and then through the FOHE:

LP-pump -> HP-pump -> FOHE

The HP pump heats the fuel somewhat, which may be enough to avoid ice accretion.

I'm not certain about the PW design.

Another point may be the structure of the FOHE fuel inlet face, which in the Trent design, as we have seen, has protruding fuel pipe ends, upon which ice may accrete.

Your point 3) has already been answered.

Bernd

T800
 

I assume Trent 800s that are not on 777s are not affected? If so this suggests it is the installation of this engine in a 777 that precipitates the problem - hence its a system issue, not just down to the engine (I assume Boeing are the DA for the complete fuel system).

I thought the T800 was only on the B777 varients?

I believe that it's 100%.

If the fix is a redesign of an engine certified part than the regulator for the manufacturer (EASA in this case) is the one that sets and approves the limitations and announces them to the world wide authorities to incorporate in maintenance actions. Of course the FAA would accept and announce them simultaneously

If the fix is a redesign of the aircraft plumbing, then it's Boeing and comes under the FAA and EASA would embrace these as well.

Dak Man

Good explanation of what appears to us (out of the direct loop) a plausible explanation of the uniqueness of one installation vs the rest.:ok:

Now if only the continued new posters would take note of these kinds of explanations before asking the same questions over and over:ugh:

Correct. Trent 800s are a 777 engine only (and not 77L/77W). These days large engines are almost invariably designed and optimised for one airframe.

If it hadn't been for B777, T800 would have been cancelled, the SIA order saved it.

Also, BA, traditionally a RR customer specified GE90 for it's initial B777 order. This was unashamedly done as part of a deal whereby GE bought BA Engine Overhal Limited (BAEOL) in South Wales, this deal also saved the GE90 from extinction at that time.

Off topic - Sorry:=

Oh, didn't know that. The optimisation is not surprising on reflection.

Still it could still be argued as a system issue, given the "end-to-end" aspects of this problem.

I'd be interested to know how the fix will be funded. If this was a car with an ABS brake problem then the manufacturer would be doing a "recall" with a free replacement of the defective item at their cost. Is it the same for an aircraft manufacturer? Would Boeing and Rolls have separate contracts with the airlines, or would it all go through Boeing? Some interesting commercial/liability interfaces here.....

Yes and interesting commercial/safety regulatory interfaces also which was what I was getting at earlier.

JFZ90
 

The airline customer would have a contract with RR almost as detailed as it has with Boeing: price, performance guarantees, support services, etc. etc.

Tenacity - Phil Gollin
 

At the beginning of the thread, everybody looked at Fuel, of course. After it tested "in spec.", I continued to question the part Fuel may have played in the accident. I took some ridicule, no problem. Turns out, the fuel is part of the problem here, though not in the "traditional sense".

Phil you seem to continue to focus on Fuel issues as well as vulnerability of other types. As far as I'm concerned, I think that is most appropriate.
The posters who wrote "the Fuel is in spec., what's your beef"??, may be the same ones who may seem impatient with your persistence. I hope you continue your line of comment.

Cavitation?? What part of the wear on the pumps was cavitation damage, and what part the pumps part time job as ice crusher? Ice is solid, if granular, sticky, or otherwise, and can abrade pump lobes and other metal pieces, with a decline in efficiency.

Upstream pipework?? Before the engine type comes into play, there is substantial icing in the plumbing, by test. What percentage of safety remains after the other types deal with it, GE, PW??

Final Note, and the most troubling vis a vis the AD. The FOHE cools Oil. Does it heat Fuel? Yes, but is that its designed task? It also melts Ice, as a casual read of the AD supports.

Relying for the ultimate safety of a/c, crew, and passengers, by tasking an inappropriate system with work it was not designed to do, seems cavalier, ill advised, and frankly, dangerous, given the information delivered thus far.

The Thrust Increase to avoid Icing, and the Idle Thrust to melt it means that half of the AD is expected to fail. This leaves the FOHE as the only line of defense to accomplish safety, yet it is this structure being redesigned, to be refit?? This is not even logical.



AF

WHBM
"How can the engine design have been in service for 15 years before such incidents happened. What caused it to work fine on comparable flights until now?"

As the AAIB report states, for the BA038 flight the minimum fuel temperature was in the bottom 0.2% of recorded temperatures. So if the system has a problem it may have taken this long for it to show up. It seems that the Delta flight came also from China but I haven't seen a temperature profile to be able to tell if it sits in the same family. Has it been an excessively cold period over these routes?




AIRFOILMOD
"The Problem isn't Ice, it's water. "In Spec." Fuel has it and at very low temps it takes shape as granular microscopic particles. As such, it does no harm. At Cruise, in VERY low temp. over many hours, the ice melts and refreezes in the FOHE.


There is no evidence that the the the freezing took place at the FOHE. I think think most now agree that ice formed upstream and was released in a relatively large quantity to the engine. The FOHE is then a likely place for the ice to stick. As the reports state testing has shown that the FOHE will block with sufficient quantities of ice.


It may therefore be prudent to improve the FOHE's handling of large quantities of ice, if Boeing cannot prevent this from occurring, but will it be enough to prevent further events? As for who should be liable for the mod and subsequent rollover. In these events it seems the engine is being supplied with fuel containing a quantity of ice it wasn't certified to live with. This would suggest an aircraft issue but I suspect RR/Boeing will jointly foot the bill.

DeScally of BC:

As long as procedures are in place to prevent at least the EDIT: one in 100,000 /EDIT chance of a repeat occurrence, I doubt a grounding order will be issued.

Here's a sampling of current major RR-equipped 777 Operators:

American
Cathay
British Airways
Delta
El Al
Emirates
Singapore
Malaysian
Thai

care to rephrase that:}

Airfoilmod hit the nail on the head in post 2261. The FOHE isn't a fuel heater it is an oil cooler. The fuel system itself isn't a fail safe design.

Having established that the current design traps ice RR and Boeing have to go to the 737 design of the fuel system where there is a bypass with a fuel heater. Those of us who flew the 732 remember well cycling the fuel heater and watching the oil temperature rise as an indication of it working.

It might also be prudent to put the bypasses back on all aircraft in particular ETOPS twins that are flying longer sectors than envisaged when they were designed.

An heart attack brought down BA038 .... analogy!
 

Warning: I'm non-professional; not crew, not engineer - just scientist guest and thanks.

A light hearted start -
the similarity of this accident with a plaque induced heart attack is interesting. Energy giving substance (food/fuel) contains substances (fats/water) that can clog and narrow energy channels (arteries/fuel lines) with potentially damaging substances (plaque/ice). Under certain circumstances these substances can break free and block the delivery of the energy substance (blood/fuel) to the engine (heart/turbine).

Quite rightly, doctors do advise the avoidance, or limitation, of the damaging substance (fats etc.) from human diets because that is the right philosophical and practical approach. However, doctors also carry out remedial action (stent insertions etc.) to remove damaging blockages, this being the equivalent of the 777/RR FOHE ice melting action.

The point of this analogy is doctors do not just concentrate on the remedial action (stent) and ignore the harmful effects of ingesting fats etc.; they study the whole system and try to recommend actions that avoid the critical moment (heart attack/turbine roll-back).

Surely this is the philosophy that the aircraft industry should follow and it is this that the AAIB is strongly advocating. That is, launch research programmes to fully understand water/ice in fuel and then make sure future aircraft systems are safer.

Of course, there is always a tension between the guardians of safety and commercial organisations - it has ever been so - and this, it seems to me, is evident in the words the AAIB use in the latest interim report.

I do hope the industry makes the effort to use modern investigative tools to fully understand the fuel it uses, to find actions that remove the danger of blockage and not just rely on the life saving operation of melting the ice!


Which brings me to observe that a 777/RR could experience more than one ice blockage event in a single flight. I hope no 777/RR pilots have been given the impression that if they experience a roll back following the step climb etc. and then follow the new SOP to melt that ice, that they will not have a recurrence on the same flight. Nor should pilots assume that if there is no roll back, following the step climbs etc., that there will not be a future roll back during that flight. You may be shouting that the probability of such outcomes is very low - maybe, but my point is that no one knows, so don't assume anything!

My vote would be to ground the fleet until the FOHE fix is in place. Why? Because I'm a coward when it comes to using my statistical bravery to risk other people's lives!

Regards, Tanimbar

Just to be safe ...
 

It would be reassuring to know that the redesigned FOHE can cope with ice pellets delivered at a greater rate than the CWT fuel scavenge system can shoot water into the main tank.

Is it possible that fuel from Chinese sources is more prone to icing than fuel from UK or US suppliers? Presumably, the investigators will have compared the molecular composition of fuels from various sources using mass spectrometers and found no differences. If so, it seems strange that both instances of roll-back occurred on flights FROM China and none have been reported on reciprocal flights TO China.

Mitigation of ice formation by redesigning pipework/FOHE is all very well but the real long-term answer is a fuel which is free from significant ice formation under all imaginable flight conditions.

Add to the list of RR 777 operators Kenya Airways.
The emotive wording of the US statement is interesting. They were much less so about 737 rudder problems and the urgency of a fix. Nothing to do with nationality of course.

What's unique about ETOPS Twins in you suggestion compared to quads :confused:

Instrumentation
 

Does anyone know if Boeing or Rolls instrumented an aircraft and flew the subject route after the events we now know about?

More Research Required
 

It's interesting that pipes accumulate ice at relatively warm temperatures, and little when really cold.

So we either prevent ice accumulation by heating, coatings or additives, or have mechanisms to avoid clogging when the ice sloughs off in warmer temperatures.

Boeing's original procedures seemed directed to fuel waxing.

It's interesting to see that the "ice" lining the pipes is not pure water ice but a mixture of fuel and water.

The Chinese fuel may have a part to play as one of the fractions may have a low temperature affinity for water.

It would be interesting to know the fuel fractions incorporated in the "ice" lining the pipes.

Two Phase materials
 

Combinations of two materials produce unique and sometimes unsuspected results. Not the least of which is mass, obviously. Without a phase affinity between Ice and Fuel, the size of the clog would be reduced. Or, clogs might not form at all.

I've mentioned before colloids, and slurries. If the Ice is particulate, it's effect on thickened Fuel may be to create this occlusive material. The picture of the Face of the FOHE with "Ice" suggests "Packed Snow" rather than block Ice. The use of the Phrase "Occluded Artery" came to mind, and I note tanimbars further metaphor.

On the One hand, further research is assumed, but secondarily and of utmost importance is providing safe Fuel Systems for the affected a/c NOW.

Simply because the Fault can be broadened into discussions of "Chinese Fuel", "political Issues", and Safety/Commercial infighting deflects the focus of what should be:

Why is the AD adhered to as a FIX? If it is, it has massive exposure to failure.

1. The FOHE is defective by occurrence and by test.

2. The AD "relies" on this defective unit to prevent and/or to mitigate something the unit has CAUSED in the First Place.

There is NO free lunch, utilizing a faulty mechanism to perform a task it was not designed to, to allow the Fleet to continue to Fly?

To answer a previous post about the difference between ETOPS and "Quads" : From my perspective....... TWO ENGINES.

AF

Spilko, refreezing is a given at the FOHE in the midst of Fault, by definition. Overcome by ICE, the "melting" feature of the unit is overwhelmed, temps drop, and the migratory Ice "Packs" and freezes at the tube ends. I see your point, and terminology is critical here. Since there is no "precedent" for this, vocabulary will wean itself of misunderstanding as the mechanism is explored.

Dark Man!

I am aware of your first point about GE Wales, but where do you get the above "quote" from...?

Dag

ETOPS
 

I am completely committed to ETOPS. It is a boon to the industry and displays elegant solutions to a number of old problems. I fear however, that the responsibles have lost sight of what makes ETOPS unique. A lofty commitment to zero failure and a disciplined and unforgiving posture toward engineering base line.

On the one hand, twins are vulnerable to OEI always, but eliminating mere redundancy involves a discipline of separation of systems. At some point in the concept, duplication of flight critical systems is inevitable. I don't think we're there yet, BA038 notwithstanding. 038 could have been avoided in a non ETOPS way, because what befell the flight wasn't a lack of redundancy, but a process that affects all formats, ICE. By that I mean the a/c was lacking in what should have been a priori engineering vis a vis ICE and its hazards.

The research thus far hasn't indicted ETOPS in any way. What is unfolding in front of the community is a lowering of standards, and a concomitant inconsistency of applying those standards. To save a penny, the authority is loosening its credibility by exposing a make do philosophy to the Public, rather than a no tolerance profile re; Safety itself. Who's in charge here.

air temperatures at cruise altitude?
 

vapilot2004:
Thanks for your insights and your list of airlines currently operating the RR-equipped 777-200ER. I note that Air New Zealand also operates this type/engine combination; eight of them I believe. Which brings me to a question I'm hoping some of you pilots can answer for me (I'm not a pilot and so thanks for allowing me to participate in this thread without hopefully generating too much eyerolling from you):

In terms of typical cruise altitudes and air temperatures at those altitudes, are there any significant differences between the northern routes on which the BA and Delta rollbacks occurred, and NZ's AKL-YVR cross-equatorial route which they fly non-stop with the 777? This is a 14-hour ETOPS route.

deScally
 

With respect, it's in here. Happy reading.

Further:

Be careful of "Fuel Heating". It is warmer temps that created the hazard, not "very cold" Fuel. (Though it was a precursor).

Location of FOHE? perhaps away from the Fan Shroud a bit.

Bypass, a no brainer. Though GE uses the concept to further cool the oil, in this case, a "recirculation" not strictly a "bypass".

The Bottom Line? The Fuel system as a whole on this combination wants to be a bit more complex, to include additional mitigating procedures and mechanicals. It always looked a little simplistic, turns out it is.

vapilot -It is always hazardous to rely on the unknown, or statistics. If what you mean is "one in one hundred thousand" of an additional occurence, think about how many months it takes the Fleet to hit 50,000 trips. At that point the chance? ONE in TWO. Let's see, 228 a/c, one trip a day, 1,000 every 4 days, twenty thousand every 80 days (Five to One), etc. See?

bernd - re:GE. The HP in front of the FOHE not only "Heats" a little, it makes any free floating ice/slurry into margaritas, "blending" the mix for the FOHE and subsequently for the nozzles. It is this architecture more than any other reason, in my opinion, that makes GE mounted 777's "immune" from "the Plug". GE-"Blended"..... TRENT-"on the rocks".

on the rocks
 

AFM,
after 2340 posts on this thread, this is the one that sums up the technical issues in a nut-shell from my point of view "GE-blended, Trent-on the rocks"
Thanks.
(I'll be interested to read bernd's take on this)

daved