BA038 (B777) Thread

[lomapaseo]

It's hard to imagine that the NTSB has sufficient data and risk assessment expertise to step in front of the public and say that the currently issued AD and incorporation schedule would not adequately minimize the risk.

It sounds more like a "me too" and I'm in charge.

[airfoilmod]

Is a BOARD. FAA is an AUTHORITY. The NTSB has forced FAA's hand. This isn't "me too", this is: "get busy". I think FAA determination will follow. Since the First mitigation didn't work (the "non-normal" one) there is great risk in merely "guessing" at a replacement, and NTSB has said it isn't acceptable anyway. The FAA diverges at great risk. The affected A/C I think will soon be parked. The NTSB's Move will temper the flack the grounding will engender, but those who complain will be criticized roundly. As I see it, it is appropriate for the Investigative Body (NTSB) to make findings of fact, then pass their work along to the rule making authority to direct a response by rule making. (FAA'S) job.

AF

[airfoilmod]

Of Ms. Osmus' letter reveals an opening left for the FAA. The NTSB anticipates a refit around maintenance schedules. This allows the FAA to come down authoritatively in ordering a fleet park.

There is some astonishing indictment of the as built FOHE as well. There are vast legal issues here, to put it mildly.

AF

[HarryMann]

On February 23, 2009, Rolls-Royce
indicated that a redesign of the FOHE was underway, and that
they anticipated the redesign to be tested, certified and
ready for installation within 12 months.Just about the time it took to redesign, test fly and put into production a complete new Mk of Spitfire and several Merlin supercharger & carburrettor upgrades :hmm:

....more than 60 years ago without CADM and with bombs dropping on one's offices and factories !

[airfoilmod]

I think from first order to first flight was 15 months for the Mustang? I'll check that. Check That, make it 117 DAYS.

AF

[RatherBeFlying]

http://www.ntsb.gov/Pressrel/2009/FOHEface.jpg

[airfoilmod]

Now THAT'S an occluded artery.

[FE Hoppy]

It's nice to see the NTSB and FAA agree with my guess from the 16th Feb 08!!

I've a good mind to name the ***** who questioned my basic understanding of aircraft systems when I put forward the idea of cold soaked system causing a restriction though the FCOC. I know it's correctly called a FOHE but I'm a bit stuck in my ways.

Where do I claim my prize?

Sorry for the cell phone interference brigade. You guys were banking on this weren't you?

:-)

[precept]

WASHINGTON (CNN) -- Federal transportation safety officials Wednesday issued an "urgent" recommendation calling for a redesign of a component on some Boeing 777 aircraft engines -- a component blamed for two major mishaps in the past year.

Authorities have called for the redesign of an engine part in some Boeing 777s.


National Transportation Safety Board investigators said the Rolls-Royce engine component played a role in the January 17, 2008, crash of a British Airways jet near London's Heathrow Airport. Both the plane's engines lost power as the plane approached the runway, and 13 people were injured in the resulting crash.

Ten months later, on November 26, 2008, a Delta Air Lines Boeing 777 was in cruise flight over Montana when an engine lost power. That plane landed safely in Atlanta after pilots performed a procedure developed in response to the Heathrow crash.

In both cases, the NTSB (http://topics.cnn.com/topics/U_S_National_Transportation_Safety_Board) said, a build-up of ice on a fuel/oil heat exchanger restricted the flow of fuel to the Rolls-Royce engines, reducing power.

"With two of these rollback events occurring within a year, we believe that there is a high probability of something similar happening again," NTSB Acting Chairman Mark Rosenker said in a news release.

The Federal Aviation Administration recently ordered operators of affected Boeing 777s to revise flight manuals to give pilots procedures to follow in certain cold weather conditions, outlining steps they should take if their jets experience a reduction of power.

But the NTSB said Wednesday the FAA (http://topics.cnn.com/topics/Federal_Aviation_Administration) action does not go far enough.
"The procedure has worked and it has been effective in significantly reducing the likelihood [of an incident]," said NTSB spokesman Peter Knudson. "But that's not enough. We need a permanent fix."
While the emergency procedures work, they add to the complexity of flying the plane and require a descent, which could be hazardous if the plane is not at a sufficient altitude, the NTSB said.

Some 56 aircraft in the U.S. fleet and a total of 228 worldwide are equipped with Rolls-Royce engines.

But the NTSB stopped short of recommending the planes be grounded. Knudson said the safety board believes the new procedures will significantly address the problem until Rolls-Royce has a new component ready for installation. Rolls-Royce indicated it can have a new system ready within 12 months, the NTSB said.

"We are encouraged to see that Rolls-Royce is already working on a redesign, and we are confident that with the FAA and EASA [European Aviation Safety Agency] overseeing the process, this flight safety issue -- even one as complex as this -- will be successfully and expeditiously resolved," Rosenker said.

The NTSB recommended that, once Rolls-Royce completes its redesign, the new system be installed on all affected Boeing 777's at their next maintenance check or within six months.

No one from Rolls-Royce was immediately available for comment.

"This is a serious matter for those airlines operating the 777 with Rolls-Royce engines," said Richard Quest, CNN's aviation correspondent . "There is a satisfactory temporary solution, but a long-term fix is what the NTSB is demanding."

[airfoilmod]

In school, "satisfactory" rates a grade of "C". Quest isn't much more optimistic than Rosenker or Knudson. I still think the NTSB, in not calling for "a grounding" has simply left the door open for their counterpart (FAA) to do so.

AF

[phil gollin]

From the NTSB press release posted above :-

"......... These recommendations are being issued in response to the findings in two investigations - an accident and an incident - involving engine thrust rollbacks on Boeing 777-200ER airplanes powered by Rolls-Royce RB211 Trent 800 Series engines. In both cases a build-up of ice (from water normally present in all jet fuel) on the fuel/oil heat
exchanger (FOHE) restricted the flow of fuel to the engine, resulting in an uncommanded engine rollback. ............" (my bold)


Fascinating.

According to this, the two investigations have been completed (at least they have specific "findings" and are factually known) as opposed to theories or speculation !

Likewise, they have supposedly explained where the additional water came to cause the problem.

Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.

.

[EMIT]

To Phil Gollin

Quote
Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.
Unquote

This problem occurs specifically on the mentioned RR engine, due to its specific Fuel Oil Heat Exchanger design. Other jet engines on other aircraft have other designs of FOHE which have not exhibited this problem, so do not loosely assume that they also need restrictions. READ information please, when it is provided is such ample detail.

[infrequentflyer789]

According to this, the two investigations have been completed (at least they have specific "findings" and are factually known) as opposed to theories or speculation !


I think it is credible that the test rig investigations have moved forward substantially from the last official reports, particularly with another incident providing another dataset. This is supported by the image provided.


Likewise, they have supposedly explained where the additional water came to cause the problem.
Because I don't think this is an issue any more. It looks from the details and the image that we are not looking at a big slug of ice collecting elsewhere and getting pulled down the pipes by the increased fuel demand, but rather it is small amounts of ice acreting at the entrance to the small diameter FOHE tubes. Increased (cold) fuel flow (as thrust was demanded) would then both cool the area and probably pull the ice into the tubes, blocking them.

EDIT: The above was based on the NTSB statement and the FOHE image, now looking at the AAIB report it is clear that the ice acretes on the pipework and is swept onto the FOHE inlet.

Leaving aside possibilities of ice in tanks not being detected or removed at sumping, there would still have been 5L or so (according to the AAIB) or water in the fuel. Looking at the FOHE image, I don't think you need anything near 5L of water to create a serious problem. Just the mechanism for small amounts to crystalise in a bad place - which is what appears to have now been established.


Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.
.If you look back on the thread there are plenty of posts identifying the Trent plumbing as different, particularly in the location of the FOHE. The Trent 800 FOHE may well be different again, sufficiently for this not to happen on other Trents.
The publication of the image strongly suggests to me that they have got this ice acretion repeatable on the test rig, in which case testing other FOHEs could have already ruled out this particular problem.

[repariit]

This from a Seattle newspaper . . .
NTSB wants Boeing 777 engine redesigned (http://seattlepi.nwsource.com/business/403191_boeingengine12.html)

"Boeing engineers, working in the laboratory, determined that the heat generated by the Rolls-Royce fuel-oil heat exchanger is not adequate to prevent moisture in the fuel from freezing. When that happens, ice can form that blocks fuel to the exchanger, starving the engines."

[airfoilmod]

To avoid Ice on FOHE, "Max Thrust is applied....". Sorry, isn't that what got This a/c into trouble in the First Place.??

To Avoid Ice on FOHE, "Idle Thrust is required...." Sorry, DELTA??

These "Mitigating procedures" were addressed. NTSB claims Another Incident (Accident) is "likely". Applied Power solutions are NOT working.

Will it now be "co-ordinated blending of high EPR followed by Idle, followed by" ....? A Secret Handshake?? Shaman? Tarot?

The way RR proposes to redo the HE frankly isn't too confidence inspiring either.

READ ##2204, 23, 42, 49, 54, 58, 59, ........ and others, ad, well, nauseum......

ReRead Osmus' letter. This isn't just "very cold temps". Neither is it "Chinese Fuel". Phil, this is a TRENT thing. Fuel has water in it, no mystery.

AF

[bsieker]

To avoid Ice on FOHE, "Max Thrust is applied....". Sorry, isn't that what got This a/c into trouble in the First Place.??

To Avoid Ice on FOHE, "Idle Thrust is required...." Sorry, DELTA??

To avoid the ice buildup, max climb thrust for step climbs had been mandated a couple of months ago in certain cold conditions.

This has proven to be insufficient in some cases. The Delta flight in question did two max. climb thrust step climbs.

To remove an ice blockage that has formed nonetheless, a few seconds of idle thrust will melt it away by changing the balance between hot oil (only a little less) and cold fuel (a lot less).


Bernd

[airfoilmod]

I cannot even infer the point you may be making. The AD is working?

It is not? It may be working? Give it time? What is your point?

AF

Delta's Idle melting excursion cost 8,000 feet. Could it have been more?
Have you seen the terrain they were flying over? At 31,000 feet they could Glide what, 90 miles? Not enough. At 31k feet, they were at most 19,000 feet AGL, Get my point?

[Low Flier]

http://www.flightglobal.com/assets/getAsset.aspx?ItemID=27976
:eek:

AAIB .pdf Report (http://www.aaib.gov.uk/cms_resources/Interim%20Report%202%20-%20%20G-YMMM.pdf)

[bsieker]

airfoilmod,

sorry for being obscure.

You said in your post that both actions (max. thrust, and idle thrust) were to avoid ice build-up.

They aren't.

One was supposed to avoid it, the other to remove it.

And I also can't see how max thrust brought any aircraft into trouble. It was only that max. climb thrust (which is usually on the order of only 30% of maximum (takeoff/go-around-) thrust) didn't keep them out of trouble.

Or maybe I misunderstood the first part of your post.

I get the point, as does the NTSB, that the idle melting procedure is not optimal, to say the least. That is why the Trent 800 FOHE design is being changed. It may take a while. What to do in the meantime? Obviously I have no answer to that.


Bernd

[airfoilmod]

Thanks Bernd. On finals, it would seem, if not already established, that increasing thrust caused Rollbacks. If so, Demonstrably the fix doesn't work. Parsing "How Much Thrust" is a fool's game. I have alluded to vibration and Acoustics on enhanced EPRs many times; this may dislodge deposits upstream the FOHE, sending them down to the Face. It also may dislodge ice accreted at the Face, further blocking Flow. That Idle may melt accreted Ice and Open the Line is wonderful, but How much is anyone willing to gamble? If it doesn't work, what then Glide Idle?

AF

[FE Hoppy]

Very interesting report. Quite a few unknown unknowns are now known unknowns.

[airfoilmod]

Reasonable to conclude from the evidence is the fact that Ice can migrate downstream to block the Face of the FOHE. Add to that the fact that Ice may have built up on the Face independently of additional "dislodged Ice". Yet the FOHE wasn't designed to be an Ice Melter; It is to be relied upon now to not only melt its own independent accumulations, but that released by "Thrust, Pitch, Turbulence"....etc.?? This is a type of Ice I suggested earlier, "Amoebic, migratory, slurry, etc." It seems to be too much for any makeshift lashup, (with respect).

AF

Post #2176 3 Feb. 09

[Smilin_Ed]

Since there have been no reported incidents with the other brand(s) of engines, it would seem prudent to consider the FOHE design(s) of those other brand(s). Could other FOHE designs not be adapted to fit the RR engines? Someone with specific experience with both/all types of B777 engines comment please.

[chris weston]

Airfoilmod sir, with the greatest possible respect you are showing your age here .............

In most (state) schools today raw results, such as the attainment of say a Grade "C", do not repeat not, rate as "satisfactory" or anything else; hitting your Mininimum Attainment Grade ("MAG") just might.

The Ofsted concept these days is more subtle and target driven as a function of your achieving "Value Added" cf datum MAG - datum MAG usually being defined as a function of a statistically derived average points score at the previous Key Stage.

On a personal note, the perception today is that in school all must win prizes and this mechanism is pretty good at diluting simplistic achievment driven elitism.

Do not expect me further to defend the current system...........

CW

[phil gollin]

Water quantities.

The AAIB Interim report no. 2 (my bold) states (page 7) that the

"... accident flight might have contained up to 70 ppm of dissolved and entrained (suspended) water ...."

whilst their post accident samples showed

".... Fuel samples taken from G-YMMM after the accident indicated that the water concentration in the fuel taken from the left main tank sump, APU line and Variable Stator Vane actuator was approximately 40 ppm ......".

However, the tests took place using 90 ppm something like 28 to 125% more than was in the crashed aircraft - as

".......the industry standard for continuous system operation tests, aiming to condition the fuel with 90 ppm of water. ......"

So, not only is the incident report rather cagey about what actually happened, but the tests do not seem (unless I missed something) truely representative of what happened. The report still doesn't explain where the additional water might have come from.

===========

However, it does look like there is a whole new bunch of research on fuel/ice mixtures to come about.

.

[airfoilmod]

Young Chris, As I understand STAR, it is an "indexed form" plateau, sensitive to the augmented mean of specific prior record, adjusted for performance diminution caused by variable but "smoothe" forms. Graphically, a hyperbolic (sic) paraboloid, truncated at x and x-y, replacing that of which we cannot speak.

AF momentus continuum, continuum truncare

[HarryMann]

The report still doesn't explain where the additional water might have come from.

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.

[deScally]

Would anybody be willing to make a guess as to the likelihood of the FAA ordering a worldwide grounding of the 777-200ER with the Trent 800 engine type until such time as a redesigned FOHE can be approved and installed? Nonexistent, small, moderate, significant...? Perhaps a silly question in which case my apologies, but it looks to this non-expert that the airworthiness directive now in place is far from ideal.

[airfoilmod]

#2273 #2274..... Probability ??..... Moderate to Severe.

AF (my opinion) (Have you read the thread?)

[deScally]

airfoilmod; thanks for enlightening me. I had read the thread, just looking for some clearer opinion re: likelihood of grounding the fleet. I await the FAA's action with bated breath. Thanks again.

[L337]

Would anybody be willing to make a guess as to the likelihood of the FAA ordering a worldwide grounding of the 777-200ER with the Trent 800

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.

[keel beam]

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?

[phil gollin]

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.

.

[phil gollin]

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 ?

.

[FullWings]

From the AAIB recent interim report:

Whilst this is considered to be the most likely cause of the engine roll backs on G‑YMMM, and is consistent with data from the incident to N862DA, it has not been possible, due to limitations in the available recorded data, to totally eliminate the possibility that a fuel restriction, from ice, formed elsewhere in the fuel system which, in addition to an FOHE restriction, contributed to the engine roll backs on G‑YMMM.
And:

Tests carried out by the engine manufacturer demonstrated that fluctuations in the P30 burner pressure, fuel flow and spool speeds, recorded on the FDR and QAR during the engine rollback on G‑YMMM, were generally more closely matched when a restriction was placed in the fuel feed pipe approximately 25 feet or more from the aircraft to strut interface.

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...

[JFZ90]

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.

[WHBM]

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 ?

[Bis47]

A solution to the early icing problems was to produce a remedy for the specific problem: fuel heaters and filter bypasses were introduced and the optimum mesh size for the boost pump inlet screens was determined. The USAF, like other military organisations, introduced Fuel System Icing Inhibitor (FSII), which can help to prevent the formation of ice.

Robust solutions ... they are available since the fifties! :ugh:

[Golf Charlie Charlie]

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

[HotDog]

WHBM,
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 ?

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

[Dak Man]

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:

[slip and turn]

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:Hoeltgen said there had been a number of cases in recent years where either a national regulator or an airline had been found to be not in compliance with EASA directives, though he declined to cite specific examples.


"In these cases, it has been up to the member state authority to design corrective action," he said. "They also have to convince us that this has been done properly."
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?

[Feathers McGraw]

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.

[bsieker]

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 ?

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.

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 ?

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

[thapr2]

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?

[lomapaseo]

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

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.

[lomapaseo]

Dak Man

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.


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:

[LHR27C]

I thought the T800 was only on the B777 varients?

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.

[Dak Man]

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:=

[JFZ90]

Quote:
I thought the T800 was only on the B777 varients?

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.

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.....

[slip and turn]

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

[Dysag]

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

[airfoilmod]

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

[spilko]

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.

[vapilot2004]

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

[lomapaseo]

prevent at least the 100,000 in one chance of a repeat occurrence

care to rephrase that:}

[sky9]

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.

[tanimbar]

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

[Rightbase]

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.

[Avionista]

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.

[Skylion]

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.

[lomapaseo]

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.

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

[Desk Jockey]

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

[RatherBeFlying]

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.

[airfoilmod]

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.

[DJohnsen]

Dark Man!

...this deal also saved the GE90 from extinction at that time.

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

Dag

[airfoilmod]

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.

[deScally]

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.

[airfoilmod]

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".

[daved123]

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

[Pinkman]

The latest advisory has deflected thinking on this thread into the mechanics of the Trent powerplant. But in reality its another cheese situation all over again, and the three relevant Cheeses are: temperature profile, fuel quality, and powerplant design. Only two of these, realistically/sensibly, can we change.

FE Hoppy and I, and one or two others way back at the beginning of 2008 said that the fuel will have had a role, and in the last few days Airfoil Mod and Spilko have reiterated that thought.

Blocking at least one hole in the cheese (Trent 800 FOHE redesign) takes care of the issue at least on the surface. But I would be more comfortable if someone could compare the performance with the current Trent powerplant flying the same temperature profile with fuels from from, say a European or a US refinery, compared to RP-3. (Jet Fuel #3, even when on spec and meeting Jet A-1 spec, can sometimes be, like Russian fuel, different compositionally to 'traditional' Jet A/A-1, if there can be said to be such a thing).

There was a statement in this thread some time ago referring to the fact that the behaviour of Jet fuel under extreme low temperature conditions was being shown to throw up some surprises in the testing following the incident, indicating that our knowledge may not be as good as we thought. Well, yes. I have said in an earlier thread why the recovered fuel may not be fully representative of the loaded fuel and in the final report I would like to see the GC/MS curves of the retention sample vs the recovered sample as well as the usual tests that define on-spec Jet fuel so we can have an educated guess at understanding the role that the fuel played - or not.

One thing I dont understand is a constant lack of reference to the retention sample. The AAIB report says that "It was estimated that the fuel uplifted in Beijing at the start of the accident flight might have contained up to 70 ppm of dissolved and entrained (suspended) water". Why estimate? Use the value that was in the retention sample which you will have analysed... or do you not actually have a valid retention sample?"

But, more generally, why should we bother? Surely if we block one cheese hole by fixing the Trent issue we can pack up and go home because the issue is fixed whether there is loads of water in the fuel or not?

The answer is we should bother because over the next five years we will see a proliferation in biofuel-based and Gas-to-liquids (GTL) based Jet A/A-1 blends some of which have known issues related to low temperature performance. The kinds of research that is now being conducted following the BA 038 incident is badly needed to ensure we can reliably predict performance and compatibility issues with, and better testing for, drop-in biojet blends which will prevent a similar incident. We need to confirm that the current testing regime - which has been in place with only a few modifications since before most of us were born - is sufficiently protective in current operational situations and with the diverse range of fuels that are about to enter the mainstream.

Can we afford not to block the second hole in the cheese by fully understanding the role that fuel played in the incident and the implications for different fuels that will be with us within a decade? That is why we must fully support the establishment of a joint FAA-EASA research and testing program that is a recommendation of Interim report 2.

Pinkman

[sky9]

There is a very real difference between twins and quads and that is the surplus of power available on twins which together with efficient wing design allows higher cruise altitudes than quads and with it lower temperatures.

[vapilot2004]

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?


You are correct of course AFM. :ok:

Then there are the people in a quiet room somewhere at Mega-Corp Airlines' home office that crunch such numbers regularly. Our regulators also play this game, something I find the NTSB and the FAA at 'odds' on constantly.

[airfoilmod]

Agreed, would have the oddsmaker a more conservative sort.

Some people confuse Warranty with Guaranty, Eh?

AF

[sky9]

Airfoilmod, yes you are correct about fuel heating, the temperature issue was addressed in the AAIB report however there is a need for fuel heating if and when the FOHE becomes blocked. An earlier suggestion in the thread drew attention to a similar problem on the DC8 that was solved by reversing the flow of oil to have the hottest oil near the inlet face.

It might be a useful addition to the OH panel to have a differential pressure light activated by sensors either side pf the FOHE, I quick cheap mod that would alert crews to a potential problem.

An alternative solution could be to have air/oilHE.

[Mac the Knife]

Unexpected ice formation in areas of restricted flow has caused problems in the past, viz. the loss of the nuclear powered attack submarine USS Thresher (SSN-593) in 1963.

"Thresher had probably suffered the failure of a join in a salt water piping system, which relied heavily on silver brazing (http://en.wikipedia.org/wiki/Brazing) instead of welding; earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints, most of which were determined not to pose a risk significant enough to require a repair. High-pressure water spraying from a broken pipe joint may have shorted out one of the many electrical panels, which in turn caused a shutdown ("scram (http://en.wikipedia.org/wiki/Scram)") of the reactor, with a subsequent loss of propulsion. The inability to blow the ballast tanks was later attributed to excessive moisture in the ship's high-pressure air flasks, which froze and plugged the flasks' flowpaths while passing through the valves. This was later simulated in dock-side tests on Thresher’s sister ship, USS Tinosa (SSN-606) (http://en.wikipedia.org/wiki/USS_Tinosa_%28SSN-606%29). During a test to simulate blowing ballast at or near test depth (http://en.wikipedia.org/wiki/Test_depth), ice formed on strainers installed in valves; the flow of air lasted only a few seconds. Air driers were later retrofitted to the high pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly."

:ooh:

[phil gollin]

As people seem to be taking the NTSB press release a little bit too far, I will repeat what I wrote in post 2282 :-

======================
======================


From the NTSB press release posted above :-

"......... These recommendations are being issued in response to the findings in two investigations - an accident and an incident - involving engine thrust rollbacks on Boeing 777-200ER airplanes powered by Rolls-Royce RB211 Trent 800 Series engines. In both cases a build-up of ice (from water normally present in all jet fuel) on the fuel/oil heat
exchanger (FOHE) restricted the flow of fuel to the engine, resulting in an uncommanded engine rollback. ............" (my bold)


Fascinating.

According to this, the two investigations have been completed (at least they have specific "findings" and are factually known) as opposed to theories or speculation !

Likewise, they have supposedly explained where the additional water came to cause the problem.

Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.

.

=====================
=====================


The AAIB interim report number 2 only indicates the possibility of the FOHE being the problem. Its experients were with fuel with 90 ppm rather than the expected maximum 70 ppm of the actual accident plane which had tested remains of 40 ppm and of which the expected maximum of 70 ppm would have been reduced by ice forming at the bottom surface of the tanks.

For the cause of the accident to be properly explained the fault must be properly explained - it is not good enough to guestimate it.

Likewise, other aircraft with various other enginge/fuel installations should be examined for possible similar problems with the new phenomomen of fuel/ice slush (or whatever they are going to call it.

People seem to think the work is over and the aviation world has the problem put to bed - there could be masses more work to come.

As for the near simultaneous fasilure in two separate systems and its effect on ETOPS I will ignore that due to total ignorance.

.

[FE Hoppy]

Some one needs to come up with an inline water extractor for fuel that can be retro-fitted the aircraft fuel systems upstream of where the ice may become a problem.

[airfoilmod]

Phil - the concurrent rollbacks are not mysterious, neither are they complicated. Nearer the engines, the Fuel systems "rejoin" in their critical attributes. The Plumbing, Fuel, and Fuel delivery systems are virtually identical, close in. Given they burn the same Fuel, stored identically, in identical ambient temps, I think I can explain why #2 quit seven seconds before #1. The #1 engine (Port) was fed from a tank in a wing that had been in the Sun flying West. The Starboard wing tank was in the shade of the Fuselage, on the North side of the a/c.

Right or wrong, ETOPS isn't perfect. Facetiously I suggested in a post way long ago, that true isolation would be served by mounting a Trent on #1 pylon and a GE on #2. "Designed Anomalous Systems" - DAS. What Else could I call it?

What I think would be fascinating is a hard copy made available of this thread. Warts and All. Informal Hangar Talk with the odd expert poking in now and again, a year long exercise in the new format of the "Pilot Lounge"

AF

[airfoilmod]

Cool the Fuel at the Refinery and filter it, removing the Ice before it gets into the a/c. You think Jet is expensive now, wow. If an a/c can separate the water in flight (Ice), I think it could be done on the ground.

"Sticky Ice" ?? Teflon Pipes.

sky9 GE "Heats the Fuel" with a second pass through the FOHE.

bernd What of the GE architecture ? (HP) in front of their FOHE instead of downstream of it?

Phil Depending on who can make the better case, "It's the Fuel", "No it's the Trent", some compromise may involve all other types. But it's a hard sell, without a record of at least an "Incident" on another non 777-200ER a/c

I also think there are folks in China hoping for another incident that doesn't involve Chinese Fuel. (Consider the foul-up outcome in China?)

Bypass, Bypass, Bypass. (Blender included, no extra charge)

AF

[Pinkman]

AirfoilMod

I told you before...stick to what you know (clearly not fuel systems)! Take the water out at the refinery (they do - there are filters and coalescers) and it will be back again by the time the fuel reaches the aircraft.

Water is removed and checked for again and again. But the nature of the fuelling supply chain and the fact that heating and cooling of fuel takes dissolved water and condenses and re-entrains it as free/suspended water means it will ALWAYS be present at low levels in aircraft tanks.

The point that I agree with you is that there are lots of other fuel related questions that havent been asked, let alone answered. Chinese Jet fuel has an incredibly low (better) freeze point than Jet (-40C) or Jet A-1 (-47C). At THAT temperature (better than - 50C) how would the GE system perform?

Pinkman

[airfoilmod]

Pinkman. What is your input on the type of Ice reported by Boeing? What about the GE architecture? Alcohol or other solutions?

I'll reel meself in if you open up a bit. Deal?

AF

One other thing before you cry Uncle at H2O in Fuel. Nitrogen transporters? Closed system pumping. May be time to build Fuels for ETOPS in water free enviros?

[andy8421]

Apologies if this question has been asked before.

I am a very frequent non-pilot flyer, and always assumed that safety was in part my responsibility. I listen to briefings, check for exits and scan this forum from time to time for news on flight safety.

I had never felt great about flying the atlantic with twin engine planes, but had taken some comfort from ETOPS certification, understanding that the chance of failure was extremely low given the testing and modelling of systems in ETOPS certified planes.

In the face of the documented problems and NTSB warnings, how is the 777 able to maintain its ETOPS rating?

[airfoilmod]

It's been asked, but perhaps not quite so well or succinctly.

First of all, it isn't 777. It is one iteration, the 777-200-ER (Extended Range). The one with the Trent RB211-800 engine fit. There are 228 of these flying.

As for your question, no one can or will say. The FAA (EASA's counterpart in America), has issued an Airworthiness Directive (AD) regarding prevention/mitigation of the problem of Ice plugging the FOHE. It is assumed that this step is sufficient to make safe this fleet of a/c for now, anticipating the development and certification of a replacement for the challenged system. When that fix is available, the a/c will be refit in some sequence deemed appropriate to the specific fleet. This is my understanding, and since an error in this forum is immediately pounced upon, I am reasonably confident of its accuracy.

AF

[Dairyground]

airfoilmod says in #2341:


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?


The statistics just don't mean that. The implication is that on analysis of several million trips (or tens of millions - I don't have my statistics textbooks to hand and my maths degree is getting a little rusty) it will turn out that the event will have occurred in about one in a hundred thousand. The statistic does not mean that there will definitely be one occurrence, and only one occurrence, in every sample of 100,000 trips. Without presence of a common causal factor, any two trips are equally likely (or unlikely) to hit the problem.

[airfoilmod]

Noted. In my job long ago as a croupier, I was taught that each roll of the dice is independent of all others. Without drifting into chaos theory, or Quanta, the odds on rolling a seven are six in thirty six. I once saw eleven straight passes at the table, the "odds" are very long. Would you place a wager on such a thing. For a pax, the odds are almost nil that a rollback will occur. A frequent pax not so nil. Pilots less so, the Carrier has the most exposure of all, except the Authority has all of it.

AF

Please note I said NOT to rely on statistics. And include the Flip of your assertion to wit: It may happen more often than one in 100,000. That it happened once is startling (look at the length of this thread), twice is astonishing, absent your "Common Cause".

No less an authority than NTSB claims a recurrence is "likely". Read the report..... Less Faeries on a pin, more on the conclusion of the lab coats.

[Pinkman]

AFM

I will reply in a PM to avoid thread clog.

Pinkman

[lomapaseo]

In the face of the documented problems and NTSB warnings, how is the 777 able to maintain its ETOPS rating?

ETOPs is based on the assumption of independent failures of the engines.like a turbine and a FADEC

EROPs includes all engine combinations including Quads and dependent failures like ice

I'm far more concerned abot fleet statistics impacting EROPs than ETOPs
but I'll leave that to the statiticians to ponder

[vapilot2004]

Chinese Jet fuel has an incredibly low (better) freeze point than Jet (-40C) or Jet A-1 (-47C). At THAT temperature (better than - 50C) how would the GE system perform?

GE matters aside, it is interesting that both roll back aircraft (Delta and British Airways) were uplifted in China.

During the NTSB testing, they discovered that ice is stickier and more troublesome not at the lowest fuel operating temps, but in the bottom third of the typical range for the flight profile. The lower freeze formulation of that particular fuel moved the range into the area of concern.

I remain perplexed as to how this was missed during the airframe fuel system & engine certification and design paths and why the problem has remained hidden until now.

[Dont Hang Up]

One other thing before you cry Uncle at H2O in Fuel. Nitrogen transporters? Closed system pumping. May be time to build Fuels for ETOPS in water free enviros?

The 777, as the biggest twin, is exploring new territory wrt operating higher (and colder) for longer. So rather than making the fuel more expensive for everyone, why not identify a solution specifically for this type of operation? A new system requirement for extreme cold exposure is implied. That RR are now urgently taking this on board is a given. Other systems designers (certainly not just engine designers) should be equally diligent.

[Ex Cargo Clown]

I don't suppose anyone has the additives that the Chinese add to the fuel to drop the freezing point ???

I have a feeling there is something there that shouldn't be there.

Failing that, anyone who comes ex-PEK, can you get a cupful of fuel and I will do a decent NMR on it, I have a suspicious feeling about all of this.

[HarryMann]

So, anyone know the RR Vs GE ratio - 777 flights out of China?

[RatherBeFlying]

Perhaps there is a specific molecule in the fuel that acts as a nucleus that collects several water molecules about it. This wax/water blob would then freeze to cold surfaces and subsequently collect its fellows.

[HotDog]

GE matters aside, it is interesting that both roll back aircraft (Delta and British Airways) were uplifted in China.

I think the fact that it has only affected the Trent 800 power plant is of more interest and significance. I have operated in and out of Beijing for many years in various types but not on B777, as have thousands and thousands more over many years. This problem has not and is not occuring on other engines.

Why can't people accept the Boeing and RR findings and recommendations?:confused:

[phil gollin]

Airfoilmod :


.............. What I think would be fascinating is a hard copy made available of this thread. Warts and All. Informal Hangar Talk with the odd expert poking in now and again, a year long exercise in the new format of the "Pilot Lounge"


Remember this is the second thread on the accident, the first one was pretty huge as well.

.

[phil gollin]

Why can't people accept the Boeing and RR findings and recommendations?

They are no more than interim.

They used non-representative fuel, and unless they are being very odd haven't managed to recreate the problem using representative fuel (anyone know ?)

-----------

In addition, the new fuel/ice behaviour needs examination and new rules written - AND all engine/fuel installations need to be examined against the [future] new rules. There may be more aircraft at risk than we know.

.

.

[HotDog]

Phil,
They are no more than interim.

Low freezing point Chinese or Russian fuel has been in use since Adam was a little boy. I am talking about exposure of this fuel for some 30 odd years before my retirement. Can you tell me why this problem has only affected the Trent800.:confused:

[grizzled]

Several of us discussed this matter waaay back. I brought up some issues -- as did airfoilmod and several others -- related to FSII. As was mentioned a few posts previously, these additives work by attracting water molecules to attach themselves to the additive molecules. It may well be that the properties of the resultant "stuff" are just not well known in long lasting low temp conditions.

Excerpt from a post from last June (18th):

“I am certainly no subject matter expert when it comes to fuels and fuel properties but several previous incidents (and a couple of accidents) keep worming their way into my thoughts when I think of this occurrence. The cases I’m talking about have this in common: Unpredicted or unexpected changes to the behaviour, consistency, lubricity, viscosity or dispersal characteristics of fuel – caused by FSII. (Contrary to what some have written FSII is not one specific chemical formulation but can be one of several compositions, including dipropylene glycol, glycerol formal, and DiEGME.) As many of you know, the amount (if any) of FSII in the fuel loaded in China could fall into a fairly wide spectrum and still be within specs. In serving this ball into the PPRuNe court, I expect (and would appreciate) comments and critique on the possibility of FSII being a factor.”

Grizz

[HotDog]

I say again, why has it only affected the Trent800.:confused:

[Pinkman]

You are asking the wrong question... the question is not "why only RR" but rather "at what point, as the temperature decreases in a given fuel will it also affect other engine/airframe combinations"?

That is the point inherent in Phil's and Grizz's excellent replies.

[Oilandgasman]

Read www.pristaerospace.co/hi-flash/details/index.html on how dissolved water comes out of solution as avaition fuel is cooled. This explains where the water came from initially. (AAIB reports 70ppm dissolved water in the fuel) The resultant ice and supercooled water then adheres to pipework in the fuel delivery system, including the small bore tubing in the inlet to the FOHE. (anyone know the ID of these tubes as they appear to be very small bore to me? ) In tests the delta P across the FOHE was observed at levels in excess of 9 barg suggesting tube blockage. (in the NTSB pic of the FOHE tube sheet, after recent testing, many of the tubes are plugged) If the fuel is heated the water remains dissolved and is not problematic in the fuel delivery system.
If you click on "history" on the above website the first instance of this type of failure is reported in a B52 in 1958, where 5 of the eight engines stopped.
Re anti icing additives the Shell Avaition website declares that anti icing additive is mandatory on all military aircraft fuel but is not necessary on commercial aircraft where the fuel is heated.
Was the fuel on the aircraft in question too cold for too long? Does cold unheated fuel on shorter flights deposit ice in the fuel system pipework and is not a problem because not enough of it has formed before the flight ends safely? If the fuel is heated what is the lowest safe temperature before the dissolved water starts to leave the fuel and become an operational problem?
As a retired engineer I am interested in this problem as I flew the same route as a passenger 8 hours behind BA038. I was in a 747 and the OAT west of the Urals was -76 C for hours. My flight was uneventful. I keep asking myself why?

[spannerless]

find this slightly concerning:

"Some small items of debris were discovered in the following
locations:

1. Right main tank – a red plastic sealant scraper
approximately 10 cm x 3 cm under the suction
inlet screen.

2. Left main tank, water scavenge inlet - a piece of
black plastic tape, approximately 5 cm square;
a piece of brown paper of the same size and
shape, and a piece of yellow plastic.

3. Right centre tank override pump – a small
piece of fabric or paper found in the guillotine
valve of the pump housing.

4. Left centre tank water scavenge jet pump
– small circular disc, 6 mm in diameter, in the
motive flow chamber."

Especially as it now appears to have been fuel starvation!

Nothing unusual there!!

There have been much worse incidents concerning things left in aircraft!

1. Inspection Engineers chair.

2. Flow pack in the tanks discovered on fuelling the aircraft.

I could go on point is to learn by our mistakes and in this case a basic design flaw may have been over looked!

luckily only a dented pride, a rather expensive insurance bill, but no lives lost!

No lives lost is the important bit!

Unfortunately as humans we a prone to Human error!

:(

and to poor grammer :E

[Machaca]

Oilandgasman:

Thanks for the link to Prist Aero (it is missing an M):
Prist Hi-Flash Anti-Icing Additive Details & Specifications (http://www.pristaerospace.com/hi-flash/details/index.html)

Cheers, M

[Oilandgasman]

Thanks M for that timely correction, some very interesting info there on water saturated fuel behaviour as the temperature falls.
O&Gman

[airfoilmod]

And I've used it, the first paragraph is deceptive. It's claim, The Water cannot be removed......(on production) is false, because it then describes how supercooled water comes out of solution in the Fuel line, to clog filters and bends, (Something I posted at the beginning of this thread).

If, on Board, the water is "removed", it could just as easily be taken out on the ground, after cooling the Fuel.

Without irritating Pinkman too much, it is eminently possible to produce and transport water free Fuel. Expensive? Oh Yeah.

But it isn't necessary.

The 777/Trent, with new architecture and a mod for its FOHE will be most welcome back into the High and Frigid Land of ETOPS. My posit......

AF

[vapilot2004]

Low freezing point Chinese or Russian fuel has been in use since Adam was a little boy. I am talking about exposure of this fuel for some 30 odd years before my retirement. Can you tell me why this problem has only affected the Trent800.

Perhaps, but we've gone from BC to AD and have come up with some new myrrhs for the lamp oils since then. :p

Seriously Rev, I think the Trent might be the canary in the coal mine and there are broader issues at work that we've yet to divine.

You ask why only the Roller, I ask how did this get past the design and certification process, and, the entire fleet of airplanes all of these years and flight hours.

[airfoilmod]

Peace. It isn't one question or the other, it's both. One is pressing, mitigation of a duplicable Fault in one specific a/c, and the other, prevention of unknown problems possible with other types. Also, what other "discrepancies" does Chinese Fuel exhibit besides low FP, if any.

Could the build up of ice in the line upstream of the FOHE in both GE and Trent meet a different obstacle (resolution) closer in? The HP in GE is "in front" of the FOHE, which also has a two pass profile for the oil, heating the Fuel more than a one pass design (Trent).

Boeing has addressed, and NTSB reviewed, the mechanism thus far. NTSB claims another incident is likely without a change in the 777-200ER. FAA has yet to speak since its AD modification. The language of the resulting Interim has "exonerated" other types, so far. Wiser, and sounder minds than mine are comfortable with the pace, what else to say??

AF

[phil gollin]

Airfoilmod ;

Boeing has addressed, and NTSB reviewed, the mechanism thus far. NTSB claims another incident is likely without a change in the 777-200ER. FAA has yet to speak since its AD modification. The language of the resulting Interim has "exonerated" other types, so far. Wiser, and sounder minds than mine are comfortable with the pace, what else to say??


NO. The tests, as far as can be ascertained, have been carried out using unrepresentative fuel. The mechanism is indicated, but NOT confirmed, and DEFINATELY NOT understood. The mechanism needs to be explained with representative fuel and a real understanding of the mechanism obtained so that new operating and design rules implemented.

The AD has NOT "exonerated" other types whether "so far" or not - have they managed representative tests on ALL other aircraft and engine installations ?

The pace may be as fast as it is possible, but it is nowhere near complete, and if the fuel/ice behaviour is as odd as the AAIB report indicates it may be many years before the whole problem is sorted out.

Is it time to panic - obviously not.

Is it time to relax - no, there is much work still to be done.

.

[airfoilmod]

Thus Far, I said. I don't claim the mechanism is understood or that anything is in concrete. I am paraphrasing the results from the report.
Rolls is designing a new FOHE, (For the Trent RB211-800 ONLY). Where have I misinterpreted the report? Who claims this situation is resolved?

No AD "exonerates" any a/c, ever. It is written and enforced to address a specific deficiency. It does not address other a/c but the 777-200ER.

It is the Trent fit 777's that are the focus here, if you want others investigated, well, you are allowed to have input to the Authority, it is encouraged. The reports claim no other type is suspect.

AF

[Der absolute Hammer]

I have not read this thread but I wonder if this feedback is interesting for you....

Sir, I am concerned at the decision to allow Boeing 777 aircraft with Rolls-Royce engines to continue flying after the crash landing at Heathrow in January 2008 (report, Mar 14 (http://business.timesonline.co.uk/tol/business/industry_sectors/transport/article5902070.ece)). I cannot help comparing the response to this accident with that after the loss of an Air France Concorde at Paris in 2000. The latter aircraft was brought down after a collision with a metal object on the runway, that should never have been there in the first place. Yet despite the aircraft being relatively blameless, the entire Concorde fleet was grounded within days pending hugely expensive modifications to the fuel tanks.
Within a very short time of the Heathrow crash landing in January 2008 it was apparent that there was a potentially serious design problem affecting this aircraft. The temporary operating procedures for these Boeing 777s, pending modifications, appear to be no more than window dressing to deflect public opinion. I have read internet forums where Boeing 777 pilots have resorted to exchanging informal ideas about what best to do if faced with unresponsive engines at the critical moments on the approach to land. This should not be happening in 21st-century aviation.
It is a letter to your Times newspaper of today. I took the guys name out just in case he-you know-offednded someone?

[HotDog]

Pinkman,You are asking the wrong question... the question is not "why only RR" but rather "at what point, as the temperature decreases in a given fuel will it also affect other engine/airframe combinations"?

So you are convinced that no other aircraft departing China with Chinese fuel on a long haul sector to Europe or US has ever experienced the range of temperatures that has affected the 777s with TRENT 800 powerplants?:ugh:

[Pinkman]

Again you ask the wrong question :ugh:

YES! I am saying that that particular set of circumstances has not happened before:

THAT batch of fuel
THAT powerplant/airframe combination
THAT temperature for
THAT duration

and THAT is why I keep saying stop focussing on THAT powerplant and look at the entire set of circumstances including the fuel.

You are obviously intelligent... why are you thinking in such a one-dimensional way? :ugh::ugh::ugh:

Pinkman

[HotDog]

You are asking the wrong question... the question is not "why only RR" but rather "at what point, as the temperature decreases in a given fuel will it also affect other engine/airframe combinations"?

Ok Pinkman, the answer to the question is: It will not affect other engine/airframe combinations.

Aren't you glad it has no effect on your glider.:ok:

[Pinkman]

It will not affect other engine/airframe combinations

But you dont know that, do you? You don't know because there is no evidence to support it either way except in hot-dog land where if something hasn't happend yet, it can't happen in the future.

How did you know I glide?

[HotDog]

Dear Pinkman, You don't know because there is no evidence to support it either way except in hot-dog land where if something hasn't happend yet, it can't happen in the future.


I have lived in hot-dog land exactly 20 years longer than you have and amassed 20,000 hours in various jet aircraft and flight simulators as a check and training airman. I think you'll agree that after a while in this industry, with the evidence and history at hand; one can arrive at a fairly intelligent assumption on the subject at hand. However, I will not scuttle your theories any further as I consider this conversation terminated. Happy gliding, a great sport! Cheers,HD.

[OverRun]

Umm, girls, wind back the fingernails. Vapilot2004 (link 2361) said I remain perplexed as to how this was missed during the airframe fuel system & engine certification and design paths and why the problem has remained hidden until now.. Good point. Missable perhaps because the certification and design used familiar and well-accepted principles, and the BA038 flight probably strayed into new territory.

I wonder if we were previously on the edge of an (as-yet undefined and only just realised) envelope and have stepped outside that envelope with this combination of aircraft, route, cold soak, fuel, testing, and specification. Not just an issue specific to the manufacturer or supplier, but rather a global issue with global consequences for the present system. Which includes engine and airframe manufacturers, and certification authorities (and not to forget the operators and crew).

Don’t Hang Up hinted at the new territory. I think it is wider than BA038 and similar operations. The new territory encompasses specifications, design and test methods, and presenting the biggest challenge of all - it questions how we will deal with the much bigger issue of the new bio-fuels. There is much work to be done (as PG said). And I think we are only at the start.

PS - Pinkman picked fuel as the cause of BA038 about a year ago, and Hotdog (The Reverend) has been contributing wisdom here for many years.

[deltayankee]

How did you know I glide?

Everyone knows. If it's supposed to be secret don't put it in your public profile!

[Pinkman]

Doh! :ugh:

[John Farley]

I went to fly a Canberra PR9 prototype back in 1964 and on looking round the cockpit I noticed a switch labelled Fuel Filter Heater. I asked "Wot's that for?" "To stop ice bunging up the works" "When should I put it on?" "When you fly high" "OK" I said.

[airfoilmod]

From 19 Feb, '08 Posts #126 and #127. See if I got close. I didn't accept the "in spec." from the beginning, so far as it eliminated the Fuel as a cause here. Always be sceptical of reports, or conclusions from any source.

Then there was that off type 777 at LAX with its rollback. Fifty feet of ice making Fuel Line is too much. Interesting read, the "Beginning". The military have been flying at 50,000 feet for fifty years, and higher, this "new" behaviour of systems, Fuel, and Ice is sounding like a red herring.

A simple consideration of the simplest causes leaves, Chinese Fuel, and/or the way the 777Trent reacts as built and engineered to conditions extant for all the history of flight; and oh yes, to Chinese Fuel.

The Lear, a Twin, is certified to 51,000 feet. They fly to China. They also have Fuel line architecture much smaller in cross-section than the 777.
Can we scale back the handwringing regarding the state of ETOPS as impacted by "mysterious new forces?" Thanks in advance.

AF

[Dak Man]

Some clarification.

T800 is not likely to have a heater matrix bypass installed as part of the FOHE, the modification concerns creating a flush fitting matrix where ice cannot accrete to the protruding ends of the matrix.

Where T800 is different, is FMU spill return. It does not recirculate back around the FCOC whereas the GE, P&W and all RR architectures (except T800) recirc spill back through FCOC.

[OverRun]

John Farley and airfoilmod – you are of course both right in your facts.

What got me was ethereal and not facts – call it gut feel, call it smelling something, call it vibrations in the ether, call it ‘away with the fairies’. I have no facts. I have no analysis. I have no scientific dissertation. If I told you the background to my concern, most people would laugh out loud - to avoid my further embarrassment, I’ll say that it is based on an “organic chemical”, as are jet fuel and biofuel blends.

I still think that there is a global issue coming with global consequences for the present fuels system. It's not just Chinese fuel. Arguable and dismissible. My only defence is that I sometimes have a disconcerting ability to see this sort of change. That sounds a bit arrogant, so let me apologise and offer Ernest Gann’s defence (as in the loose elevator bolt over California AFAIR) – blind dumb luck leads me to my conclusions.

[airfoilmod]

Taking note of your clarification, I would question the efficacy of shortening the tubes to terminate flush with the tubesheet. As it is, migrating Ice, when encountering the current design, has the ability to pass by the openings of the tubes and collect between them, for a time, held out of harm's way. The mod may have the advantage of collecting the tube openings closer to the Oil, (the Heat source), but the volume of Ice has nowhere to go but collect at the respective openings into the cannister. From a manufacturing standpoint, it appears a less complicated termination, (the Fix), simply with better access for the welder.

John Farley's anecdote about the Canberra is most instructive, a simple solution provided by a straightforward anticipation of the problem. A filter to remove solids (Ice) from the Fuel Flow, combined with a Heater to melt the Ice and return it? The Canberra was a very high flier; one should question the approach by Boeing/RR about the 777 design.

Over Run - I admit to the same experience. One who ignores any of his senses in flight is not using all his skills.

AF

[sooty655]

Airfoilmod
The mod may have the advantage of collecting the tube openings closer to the Oil, (the Heat source), but the volume of Ice has nowhere to go but collect at the respective openings into the cannister.


I would guess that the intention is to provide a smooth rapid flow into the tubes to hasten the icy slurry through. The pockets around the protruding tube ends will be stagnant areas and encourage the stuff to stick.


Dak Man
Where T800 is different, is FMU spill return. It does not recirculate back around the FCOC whereas the GE, P&W and all RR architectures (except T800) recirc spill back through FCOC.


I have been revisiting the fuel system diagram posted by Jet II at post 467, and it shows the LP fuel filter after the FCOC, which also seems to me to be an unusual arrangement.

Anyone out there know why the T800 is like that?? :confused:

Sooty

[airfoilmod]

Without adding pressure by placing the HP in front of the FOHE, there will be no real change in Ice migration at the Face, as I see it. Clipping the tubes flush seems an improvement, but hardly a solution. As the migrating Ice hits the entry, it still has the same cross section to contend with, and I still think of the interstices between tubes as a plus for temporary "storage" of the slurry. The closer proximity to the Oil entry in the cannister is a plus, though.

The HP pump is a geared, or lobed mechanism, a positive contact type that would certainly serve to crunch solids or gels into a pumpable mass.

Placing this unit in Front of the FOHE would prevent solids from accessing the Face, as GE does. It was the Plug at the Face that caused cavitation, the HP has no flow/fault relief valve to relieve pressure when draw is prevented. Including the products of spill to cycle through the HP feed would be an alternate supply, or direct connect to HP from FOHE Face bypass would prevent cavitation also. But this would preclude using check valves in the spill return, otherwise cavitation could occur.

[spannerz20]

Airfoilmod

I was allways under the impression that having the HP fuel downstream of the FOHE was a failsafe design. The theory being that if a pipe within the exchanger ruptures the oil is at a higher pressure than the fuel. This leads to the oil contaminating the fuel system but the engine can combust this. Conversely If the fuel were to contaminate the oil system the lubricating properties of the oil would quickly be lost causing damage to the engine.

I Can't remeber the architecture of the GE system so I don't know how they get round this ?

[airfoilmod]

What I'm after is the masticating ability of the gears in the HP to blend the Ice back into the Fuel. Bernd posted a while back that GE's HP is upstream of the FOHE.

If it takes different metallurgy for the pipes in the FOHE, or a pressure sensor in the oil portion of the cannister, or a bypass around the FOHE downstream the HP and directly to the nozzles, these are design considerations. It seems to me, though, that if the Oil gets into the Fuel system, it will deplete and cause engine damage anyway. One way round this HP FOHE is a partial bypass. Why direct 100% of the Fuel through the FOHE? Why not a portion of it, enough to cool the oil only.

The FOHE has been shown to be the weak link. Are there others? The Ice picture from the Reports is daunting, no doubt. There remain two issues:
Refitting the Trent/777 immediately, and an intense program of Fuel Research.

[spannerz20]

I would have to dig the notes out again but I think with oil contaminating LP fuel the rate of oil depletion is much less than HP fuel contaminating the oil thus buying valuable time with the engine still running.

Like you the I found the picture of the Ice accretion very worrying and the modified FOHE can't come soon enough. Practically the retro-fitting of the new units won't happen overnight, with 500+ Trent 800's on wing manufacturing and supplying the units post certification is a logistical challenge in its self.

More research into fuel will definitely be a good thing. The fact that a lot of the design regulations are based on 50 year old research indicates to me that this is long overdue !

[Pinkman]

I'll admit upfront that I am not an engineer - I am a refining & fuels guy with the oil industry. But I was struck by the fact that AAIB interim report 2 clearly reported that ice accumulated on the face of the FOHE and melted fairly rapidly until the test rig became too cloudy to see what was going on. Surely the idea must be to increase the transfer of heat between oil & fuel. How does remachining the physical face of the FOHE achieve that? Surely you either have to increase the recirculation rate of the oil or elongate the matrix to improve heat transfer. As I am clueless here I am happy to be abused on this!

Pinkman

[airfoilmod]

As I see it, the extension of the tubes past the Face into a 100% Fuel (cold) environment allowed Ice to accumulate and prevented it from reaching the hotter portions of the HE, the Face. As Sooty says, the goal seems to be to expedite the Ice's migration directly to the Face itself. The schematic I have seems to show the From Engine Oil entering the FOHE at the Fuel exit. The FOHE Away Oil (cooled) seems to be exiting at the Face FOHE. I'd like to be wrong, since I think the Hottest Oil should be at the FOHE's Face.

My question is the region between all the tubes can accomodate some volume of Ice, and trap it out of Harm's way (theoretically), unless the slug of Ice is too large for this and then plugs the 1080 openings. In any case, though helpful, I don't think the foreshortening of the tubes to the Face accomplishes enough to solve the problem.

BA038 Rolled Back after an increase in Fuel was commanded, and the Thrust increased. Did the vibration of added thrust shake loose a quantity of Ice that then occluded the FOHE's? If so, what purpose does the AD's call for occasional max thrust solve? Then return to Idle to melt whatever accumulation has presented? The AD seems insufficient. The GE and Pratt engines, not having had a rollback (seemingly) does not mean they won't or that they haven't and weren't diagnosed properly. The RR fix seems short of the mark. If the AD is used, should it coincide to proximity to an alternate?

AF

[phil gollin]

I would again point out that the ice accretion photo, tests, etc.... have all come from UNREPRESENTATIVE tests using unrepresentative fuel.

Before trying to redesign everything, a proper understanding of what actually happened and the "new" fuel/ice behaviour is needed.


(I will now go back to sleep until the "accumulation" of posts ignring the facts starts to build-up to a critical level again.)

.

[bsieker]

Surely the idea must be to increase the transfer of heat between oil & fuel. How does remachining the physical face of the FOHE achieve that? Surely you either have to increase the recirculation rate of the oil or elongate the matrix to improve heat transfer. As I am clueless here I am happy to be abused on this!

No, the rate of heat exchange has been designed the way it is. Having more heat exchanged may make the oil too cold. The other name for the FOHE is "Fuel Cooled Oil Cooler", which clearly states is primary function: cooling the oil. Heating the fuel is only a secondary effect.




The schematic I have seems to show the From Engine Oil entering the FOHE at the Fuel exit. The FOHE Away Oil (cooled) seems to be exiting at the Face FOHE. I'd like to be wrong, since I think the Hottest Oil should be at the FOHE's Face.

Countercurrent flow heat exchangers are much more efficient than parallel flow desings. The design goal of the FOHE was not to melt ice on its fuel inlet face, but to cool the oil, and weight being a critical parameter in aviation, this was obviously the right engineering decision. I'd be surprised to see a lot of parallel flow HEs anywhere.


Bernd

[Dak Man]

I have been revisiting the fuel system diagram posted by Jet II at post 467, and it shows the LP fuel filter after the FCOC, which also seems to me to be an unusual arrangement.

Anyone out there know why the T800 is like that??

Sooty

This is a normal arrangement, LP Pump - Oil Cooler - LP filter (with bypass) - HP Pump. Nothing unusual in that system and it's comon to all 3 big manufacturers.

Again, where T800 is different is the return circuit of spill flow (that flow delivered to the FMU in excess of what the burnt flow demand is) which is not an inconsiderable amount of fuel. On T800 it spills around the HP system in most other applications it spill around the LP system therefore introducing a large heat source into the FCOC.

Also, it is normal practice to arrange the flow path so that the hottest oil is cooled by the coldest fuel.

However, the effective "fix" is, in my opinion, treating the symptom not the cause, which is essentially fuel with high entrained water content.

Controlled testing of the engine fuel system whereby a "slug" of ice or "snowball" is introduced into the LP inlet is extremely difficult to control and replicate that which develops in the aircraft system.

As has been previously stated the engine fuel system has been optimised within the aircraft flight envelope, I do not know the intimate detail but it appears that there may have been some envelope excursion with BA0038 which the engine fuel system was not designed to accommodate, combined with the upload of fuel that may have had a high water content and the result could be considered as academic.

For information engine fuel system ice testing is carried out at a concentration level of ~260ppm.

[Pinkman]

That is why I continually ask what the results were from analysis of the 'retention' samples from the airport tankage. Practices vary; in the old days deliveries often had a representative sample from the bowser taken and it was sealed in something resembling a kilner jar with wire seals and a lead crimp.

Nowadays with hot hydrant systems the procedures aren't much changed: Ideally (i.e. CAP 748) there should still be a sample taken:

a) immediately before receipt into the fuel installation;
b) after receipt of fuel into the fuel installation (after settling time);
c) each day before the first delivery from the fuel installation;
d) after prolonged heavy rainfall or snow;
e) after de-fuelling;
f) after vehicle washing;
g) immediately prior to fuelling an aircraft.

Soooo.. again, I ask, where are the samples, were they subject to a proper Chain of Custody arrangement, and what are the analysis results?
It would be nice to see some records of the last delivery into tankage and the total rainfall increments between the delivery and the fuelling.

Pinkman

[Jumbo Driver]

Countercurrent flow heat exchangers are much more efficient than parallel flow designs.

Why is this?

Also, it is normal practice to arrange the flow path so that the hottest oil is cooled by the coldest fuel.

Is this not the opposite of bsieker's assertion ?


JD
:)

[bsieker]

Quote:

Countercurrent flow heat exchangers are much more efficient than parallel flow designs.
Why is this?

Basic thermodynamics, really.

Ideally, a countercurrent flow HE can make the "hot" fluid (oil) at its exit almost as cold as the "cold" fluid (fuel) at its inlet (when it is coldest).

Ideally, a parallel flow HE can make the "hot" fluid (oil) at its outlet only almost as cold as the "cold" fluid (fuel) at its outlet (when it is warmest).




Also, it is normal practice to arrange the flow path so that the hottest oil is cooled by the coldest fuel.

Is this not the opposite of bsieker's assertion ?

It is. And I think Dak Man might have been momentarily confused when he wrote it.

Because what he said also means that the hottest fuel would be used to cool the coldest oil, which would be inefficient.


Bernd

[Oilandgasman]

Countercurrent exchange - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Countercurrent_exchange)
Here is a very basic diagram on the difference between the two. Showing that counter current exchange is the more efficient. This of course will only apply if the lube oil bypass on the FOHE is closed. If it is open then little heat is transferred to the fuel. As the lube oil flow through the shell side of the FOHE is a torturous path across the many tubes and around the baffle plates, it would be interesting to know how far the bypass needs to be open before there is no flow on the shell side of the exchanger and therefore no heat input to the fuel. Are we sure that this exchanger arrangement is counter current flow? If it is concurrent then less heat transferred to the fuel even when it is fully in service.

[airfoilmod]

The Fuel flow is 6,000 pph at Idle, and the Fuel is very cold.

The Oil Flow is what? Far far less?

The Oil side of the HE is exposed to almost static low temps, it affects the Fuel very little.

At the critical time being discussed, (FOHE plug, Face) the Hottest Oil would be most effective at melting the Ice, per AD. But remember, as I pointed out a while back, the FOHE is not intended to be an Ice melter, it is an Oil cooler. So the design of concurrent or counter is not relevant to the discussion; except insofar as an installation is now intended to accomplish that which it was not designed to do. Solving the Plug problem doesn't solve the Ice problem. Until Pipe Ice is eliminated, someone's tilting at windmills. The Trent may be taking the fall for a problem no engine was designed to function with, but happened to be more vulnerable to, (the Ice), by chance, than the other engines.

AF

[Dak Man]

Perhaps my post was slightly misleading, there is no hottest or coldest fuel "end", the fuel temp is what it is and is largely uniform as it enters the FCOC, again remember that it's an oil cooler - not a fuel heater but you can take "benefit" from the hottest oil in raising fuel temps at what is evidently a critical point in the system, i.e the heater matrix end plate.

The fix that I mentioned is, in my opinion, little more than a sticking plaster, if the focus is to be an engine fuel system orientated fix then it should be focussed on getting a bit more heat to fuel in the FCOC loop, and as I have said previously this is normally achieved via the FMU spill return to LP rather than HP as in the T800.

However, in saying that, does anyone know what Fuel Return to Tank (FRTT) philosophy is for B777 / T800, this may well be an insufficient Flow Number (FN) for these extremely long sector cruises and not prevent the tank fuel volumes dropping below say, -8 Deg C.

I suspect that if system testing is done with fuel in the sticky ice temperature window then lots of engine fuel systems will, shall we say, "fall down" which is a huge can of worms. It's perhaps somewhat fortunate that it was a T800 where a fix is easily "sold". If it had been a GE90 where I believe the FCOC loop is in the HP fuel circuit, therefore intrinsically hotter, then the proverbial would be hitting the fan. As an aside the problem with HP side FCOC loops is matrix tube failure, as significant oil dilution would occur leading to lubrication / bearing "issues".

Again, fundamentally the engine is being asked to deal with an aircraft fuel system phenomena, not exactly chicken and egg.

[airfoilmod]

If HP upstream is problematic for tube failure, why did GE choose the design? The Fuel as heating fluid may not be GE's strong suit, but it's HP design. Again, the Fuel does not gain much Heat, it wasn't the design issue. The idea would be to Heat the first place Ice forms, which is not the FOHE. As a final fix, if it is the FOHE that is to remediate the Icing problem Plug, it's the same as accepting the presence of Pipe Ice. As a final fix, that is ludicrous, for reasons stated above.

AF

[sooty655]

I can understand the suggestion that placing the FOHE after the HP pump may protect the GE system by "mashing" the ice to slurry in the pump, but doesn't the GE arrangement have an LP filter? :confused:

If so, the ice would collect there, and presumably melt eventually, and any blockage would be relieved by the bypass.

[Rightbase]

With nice clean fuel and nice clean oil, it doesn't matter which flows through the little tubes, and which flows round them.

But if the fuel is lumpy, perhaps because some water has been pumped into it via an exceptionally cold main tank, it might be better to put the nice engine oil through the little tubes, and let the lumpy fuel go round the outside.

[airfoilmod]

Thing. And Ice wasn't a design constraint. IMO.

Sooty - I can't find the GE schematic. The RR has an LP Filter downstream the FOHE, and appears to be embedded in an Oil flow system as is the Fuel. The LP seems to be an Impellor design, the HP a lobed, or geared design. So the Fuel goes unimpeded from Tank to LP to FOHE. (Roughly).

Only in Hindsight, and knowing Pipe Ice is a Real problem, are all these comments pertinent. But it would seem that putting the FOHE as the skinny kid, closer to the Nozzles, may have prevented Trent from taking the flak. But then we wouldn't be aware of the Problem at all. Perhaps never. So far, a totalled Bird, a broken leg and some brown Laundry offloaded Delta at Atlanta. So Far.

RightBase - To be fair, the FOHE wasn't designed strictly for high and cold. Down low, and warm, the Oil is in more need of cooling than up high, where most everything's cold to begin with. To get best exposure to the Fuel (which isn't so cold when low,) the design (IMO) slows the Fuel down, by necking down the cross section and adding surface area F/O.
Gives the transient Fuel more time to soak up some calories. Ice? What Ice. The increase in pressure and slower velocity becomes problematic up high, especially when Pipe Ice can occlude the passage. Which is what is frustrating, where the Oil isn't so hot, and the Fuel is very cold, the need for an FOHE is debatable, especially when Thrust is way short of TOGA or Cl. Hence, why not a (relatively) simple bypass for the Fuel? The Oil has one, it bypasses the FOHE when it cools down, Shouldn't the Fuel bypass at the same time? Or in an Icing regime?

AF

[tanimbar]

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

The thread has now turned to an area that intrigued me some time ago (419, page 21) and caused me to write the following.

An article on smartcockpit, written by an Airbus employee, on Low Fuel Temperatures has a table listing the Minimum Inlet Temperatures for engines from various manufacturers. RR has temp of 3C (This figure seems generalised for RR).

The question, for those that really do know the answer, is what happens next if the fuel heat exchange systems cannot raise the fuel temperature to, or above, 3C?The question was not answered then but I'm hoping one of you will be kind enough this time.

Thanks in advance.

Regards, Tanimbar

[Dak Man]

ImageShack - Image Hosting :: ge90dacb777.tif (http://img25.imageshack.us/my.php?image=ge90dacb777.tif)

Indeed Sooty the GE90 does have an interstage LP filter which would go into bypass if clogged with ice. When in bypass the ice can migrate and block the bypass loop, cavitating the HP pump and ceasing all flow to the FMU.

Edit.

Having had a closer look at the GE90 schematic I was mistaken here, the LP filter (and hence bypass) is in the HP loop so the chances of ice ever getting there is slim as it would get mashed in the HP Gear Stage. However there is no bypass loop for the interstage strainer :(

[sooty655]

...to collect in a GE90 interstage strainer (or block a T800 FOHE) but not enough to fill the strainer and overspill into the bypass. I wonder if there are any records of GE90s with transient high strainer dp or bypass opening - would the pilot be aware of it?

It may be that variable conditions (and thus probably variable quantities of ice released) make the GE90 also an accident waiting to happen. :eek:

Sooty

[Dak Man]

Fuel systems are routinely Qualification tested with fuel temperatures down to -54°C in the tank and -45°C at the LP inlet. It's fuel in the region of -8°C that is causing the headaches.

[tanimbar]

You said,
It's fuel in the region of -8°C that is causing the headaches. .

I know. I should have made it clear that my question arises purely from curiosity. I'm not implying anything by asking, "What happens next if fuel at or below 3C enters an RR engine inlet?".

Regards, Tanimbar

[Dak Man]

Nothing untoward.

This table you mentioned seems a bit suspicious to me.

As I've said the engine fuel system is designed to accept fuel (with 260ppm of water present) at the LP inlet down to -45°C (fuel temp) without issue (and they do). What is now evident is that this is possibly not the worst case scenario due to the type and formation of ice present.

This kind of system icing testing has in the past prompted modifications to FMU Flow Washed Filters where sevo flows are traditionally tapped off. Obviously if a flow washed filter becomes clogged (it shouldn't because as it's name applies the filter is constantly "flow washed") then you can lose control of the engine as VSVA contol et al are servo flow controlled / powered.

[tanimbar]

Thanks for the reply. I think we might not be discussing the same thing.

If I understand the Airbus article properly ( http://www.airbus.com/store/mm_repository/pdf/att00004900/05_fast_36_low_fuel.pdf ) then the 'minimum engine inlet temperature' is the minimum temp. the fuel should be AFTER passing through the 'oil cooling system', i.e. the fuel is about to be burnt.

To quote from the article, paragraph entitled Minimum Inlet Temperature,

Engines have an oil cooling system at their inlet, which uses the arriving fuel as a heat sink, thus warming it. Various system architectures and hardware leads to a varying specification of the minimum temperature that a given engine type can cope with.The minimum temperature is expressed as a margin versus fuel freezing point - the minimum engine inlet temperature is the actual fuel freezing point with the manufacturers margin added to it (see right-hand table).Of course, I might be completely misunderstanding the terms used and their meaning, in which case I'll find a dark corner .......

Regards, Tanimbar

[airfoilmod]

Twinops. Global, 12,14 hour sector over saltwater and/or Granite ops.
OEI ? OK, worst case. Hmm...Not after BA038. It is difficult not to oversimplify the problem. The fault? Mostly with Gross Fuel architecture.
Pipe Ice. A look at the difference in systems RR/GE? Not much, and given that both firms have been building powerplants since Frank Whittle invented the format, (Apologies to Messrs. Pratt, Whitney), it is not completely accurate to find fault with the engines. Wings Ice, it is a fact of Life. Fuel has water in it, likewise a fact.

Redundancy in ETOPS. Don't forget, that was what was eliminated. Not added. Safety no longer in numbers of engines, but in engineered dependability. At a certain point, the Fuel path is symmetrical, common, undifferentiated. Isolation of systems isn't the solution; the solution may be additive symmetry. If it turns out that Fuel simply is what it is, wet, then as the Fuel closes in on the nozzles, perhaps adding alt. fuel as an option on the Flight Deck may return some "fails safe" to the flight.

In other words, relying on Two Engines is a proven concept, proven.
A step backward to a bypass, or "branched" system, rather than pinning all reliability on a "single pass" system might be worth looking at.
Weight? Cost? Of course. But as the Fuel necks down to ever more critical pathways, an alternate Path might be attractive when Ice becomes a factor.

Earth, The Water Planet.

[lomapaseo]

Discussions about Twin engine operations don't belong in this thread :=

[Flight_Idle]

I'm curious to know the bore of the pipes in the FOHE which the fuel passes through. Looking at the photos, I've guessed at 6mm, am I far out?

[Rightbase]

My light hearted observation was prompted by an assumption that since there is no (significant) net heat gain, one fluid body loses as much heat as the other gains, and a second assumption that it would work as well whichever was the hot side, and whichever was the cold. Add the (uninformed) gut feeling that the tubes were more vulnerable than the shroud to blockage, and I'm there.
To get best exposure to the Fuel (which isn't so cold when low,) the design (IMO) slows the Fuel down, by necking down the cross section and adding surface area F/O.
But reflecting on your post, the contact times for a plug of each fluid are not necessarily the same, so maybe the symmetry is broken...
the need for an FOHE is debatable, especially when Thrust is way short of TOGA or Cl. Hence, why not a (relatively) simple bypass for the Fuel?
There is no difference between us in the logical need for a bypass mechanism. I just liked the idea of a (very) simple one that does not rely on a moving part, and which puts any ice right in the heat exchange zone. Can I have it as well, please, just in case the (relatively) simple one with a moving part gets wedged open by a lump of the ice solid in below zero fuel when TOGA is needed. That scenario would be the very devil to diagnose from the expensive later consequences.

[sooty655]

The design basis is that it is an oil cooler, not a fuel heater.


the contact times for a plug of each fluid are not necessarily the same


That is why the oil takes a convoluted path around the tubes, diverted back and forth by baffles, to ensure a (relatively) long residence time in the cooler and thus maximum cooling.

The fuel is supposed to go straight through the tubes and out the other end, with minimum restriction to the fuel flow. Very little heat from the oil passes to any particular molecule of fuel, but that doesn't matter because there is plenty more cold fuel coming along behind.

Of course, the guy who designed it that way didn't know that lumps of ice were going to be thrown at it. :uhoh:

If you swap the flow paths between fuel and oil, the result will be warmer fuel and much less well-cooled oil.

[bsieker]

If you swap the flow paths between fuel and oil, the result will be warmer fuel and much less well-cooled oil.

Sorry, that is thermodynamical nonsense.

If the fuel would be getting warmer, it would mean that more heat (energy) was transferred to the fuel. All energy that is transferred to the fuel, must come from the oil (disregarding other heat sources for the sake of the argument), which means that the oil would also be cooled more.

What you state above might be true if the flow rates would also be exchanged along with the flow paths. But that is not possible, since both the oil and the fuel flow rates are dictated by operational conditions.


Bernd

[airfoilmod]

The FOHE cools Oil. Fuel flows through 1,080 tubes with spaces between all of them between Face and Exit. This reduces cross section and increases Pressure and transit time. But the Oil gets cooled. There is a bypass for the Oil when further cooling is unnecessary, yet the Fuel must still transit the FOHE, regardless of Engine Demand. At this point, if max Fuel is commanded, and no Oil is being cooled, why, in your opinion, must the Fuel continue to flow through this necked down passageway, just to get to the HO side of the pumps for the FMU?

What is your opinion of the GE architecture: HP upstream the FOHE?

rgds.

AF

[bsieker]

,

The FOHE cools Oil. Fuel flows through 1,080 tubes with spaces between all of them between Face and Exit. This reduces cross section and increases Pressure and transit time. But the Oil gets cooled. There is a bypass for the Oil when further cooling is unnecessary, yet the Fuel must still transit the FOHE, regardless of Engine Demand. At this point, if max Fuel is commanded, and no Oil is being cooled, why, in your opinion, must the Fuel continue to flow through this necked down passageway, just to get to the HO side of the pumps for the FMU?

Not knowing, as we assume the designers did not know, that ice may be a problem, the question is: why not?

The fuel delivery system, including pumps, filters, and the path through the FOHE is obviously designed to be able to deliver maximum fuel flow needed for TOGA thrust, and then some.

Without our hindsight, nothing would have justified the additional weight and conplexity of a fuel bypass.


What is your opinion of the GE architecture: HP upstream the FOHE?


I'm not a fluid dynamics engineer, so I would have no opinion on that. I assumed from earlier pictures I saw that GE had a different layout of pumps and coolers than the Trents, but now I'm no longer so sure. I've read here with great interest about benefits and disadvantages of different designs, but I'm not in a position to judge any of that.


Bernd

[HarryMann]

Without our hindsight, nothing would have justified the additional weight and conplexity of a fuel bypass.Weight, weight, weight...

Honestly, weight is really not a problem these days on commercil aircraft when we are talking of a few pounds, seriously.

Think of just a crew putting on a few pounds each, let alone big blokes Vs small blokes, or the whole pax... or just a gallon or two extra fuel - honestly, things are NOT that critical that it would come into a design engineer's decision when safety is an issue.

Complexity Yes, weight, No!

I've seen parts fail on light aircraft because ONE pivot pin was made 0.020 " too small dia. when to have made a 1" long pin twice that diameter would add about a gram - and people die :ugh:

[airfoilmod]

Engine designs, GE and RR, have "bypass" for Fuel. It is at the FMU in the Trent, and the HMU in the GE. In this case, Fuel in excess of combustion requirements, (Spill) returns to the HP via dedicated plumbing.

I would agree "weight" isn't an issue for an additional bypass for Fuel around a clogged or malfunctioning FOHE (F/O HX in GE). I also don't think complexity is an issue; GE has some complexity that Trent does not.

The GE design has three separate Heat exchangers, Trent only one.
Two of the GE's units are included specifically to mitigate Fuel icing.
The Main HX and the Servo HX are paired in the Low Side, and the schematic states they "Prevent Fuel Icing". An additional HX uses separate sourced Fuel to cool the Gearbox Oil.

Here I need to back track and perhaps apologize. On different occasions I have read here that GE's HX is downstream of the HP Fuel. I now believe that not to be the case. It remains a question; the schematic I use is a simple one, the orientation of the Main F/O HX cannot be perceived conclusively. In bsieker's post #2316 he demonstrates his idea of the critical architecture, HP in front of HX. This I think if not wrong, is not accurate to certainty.

To be quite fair, though the schematics I study are from a common source, again they are not blue-line exactly, and I regret any mistaken conclusions I may have encouraged by being so convinced of conclusions by others and myself.

This leaves a major discrepancy. GE in its schematic clearly has addressed Fuel Icing (potential) in the text of their document. Rolls has not. This does not mean Trent didn't consider Ice in Fuel, just that they didn't mention it in their schematic's text. Include a reasonable vulnerability in the architecture relying on one FOHE, without Heat, (Other than Oil), or Flow Bypass.

NTSB's release and letter continue to shadow the 200-ER. I still don't see the proposed mod to the FOHE as a "Fix". There may be other steps in Rolls plan, but without knowing what they are, the change doesn't address the known Icing other than to try and keep it melted. A very abbreviated Fuel testing program brings up new worries; it didn't solve anything, and really hasn't even identified the specific problem or its potentials.

AF

[sooty655]

Originally Posted by sooty655
If you swap the flow paths between fuel and oil, the result will be warmer fuel and much less well-cooled oil.

Originally posted by bsieker
Sorry, that is thermodynamical nonsense.



Mea culpa. I forgot to allow for the flow rates.

However, I stand by the original description of why the flow paths are chosen the way they are.

Sooty

[bsieker]

Keep in mind
The Fuel flow is 6,000 pph at Idle, and the Fuel is very cold.

Just to get the facts straight. Idle fuel flow is less than 1,000pph (see first AAIB interim report, p.4, second paragraph), at which flow rate the difference between counter- and concurrent flow designs may become significant.

In the case of BA flight 38 the engines rolled back to between 5,000 and 6,000pph, which was still not as much as demanded, but significantly more than idle.

It is also worth noting that that reduced fuel flow was not low enough to allow the ice to melt sufficiently quickly (or at all), whereas all tests indicated that idle fuel flow was low enough.

Two more things to consider:

- would 6,000pph in a parallel flow design have been low enough to allow the hot oil at the cold fuel inlet to melt the ice?

- would a parallel flow design FCOC of the given size have enough oil cooling capacity at idle fuel flow?

I cannot answer either of these questions, but I assume RR engineers are already looking at them (and a lot more.)


Bernd

[airfoilmod]

What I had in mind, 1.15 EPR, not Idle. My mistake. Think about your 1,000pph. The 895 burns just 200 gallons an hour at Idle? Who'd have thought.

AF

[sooty655]

Originally Posted by bsieker
Would a parallel flow design FCOC of the given size have enough oil cooling capacity at idle fuel flow?


Swedish Steve has pointed out that the T800 also has an air-cooled oil cooler - presumably this is intended to cover for any lack of cooling capacity at low fuel flow rates.

Sooty

[airfoilmod]

I would think that the AOHE is a backup for a system that at times, works too well, the Fuel. Thermodynamically, air is not efficient compared to liquid. Up high, where Ice is forming, the Oil runs cool, and the FOHE isn't as critical as Low, where Thrust demands are high, variable, and the Fuel is warmer. My picture of the Delta flight is high cruise, very cold temps, Icy Fuel Pipes, and not much need for Oil Cooling. So when the FOHE packed up, it wasn't in danger of being unable to cool Oil, but in causing Fuel Starvation. Had the phenomenon been addressed, there would have been an Alternate Fuel path available, sensed by diff. Pressure at the FOHE "ends". IMHO

AF

[LAS1997]

I hear that they are breaking up the aircraft at LHR, does anyone have pictures? I understand that the cockpit has been cut away, perhaps to be converted into a simulator?

[CONF iture]

Just to get the facts straight. Idle fuel flow is less than 1,000pph (see first AAIB interim report, p.4, second paragraph)
That's correct for high FL ("first few minutes of the descent") but at low altitude the idle FF per engine must be closer to 2200 pph and even 2600 pph when in landing configuration.

[Avionista]

From a contractual standpoint, where is the physical boundary between Boeing's sphere of responsibility and that of Rolls Royce, the engine supplier? Would it be in the area where the engine nacelle attaches to the wing pylon?

Presumably, the contract under which RR supplies its engines to Boeing would include detailed specifications regarding the nature of the fuel composition/condition to be delivered by the 777's fuel system at the Boeing/RR interface. It seems unlikely that the contract would have specified the sort of volume of water/ice which arrived at the FOHE. If so, RR could argue that the fuel delivered to its engine was outside specification and, therefore, they (and their insurers) are not liable for the loss of the aircraft.

[cwatters]

I doubt the contractual boundary is in the same place as the physical boundary.

[airfoilmod]

The 777 supplies (3rd Party) Fuel to any of several engine types. In the case of the GE, where fuel icing is addressed in the design, there have been no reported rollbacks, so at first blush, the uphill path is RR's. But it is not that simple. Sub contractors for design, materials, manufacturing, testing, delivery, spares supply, transit, indemnity, Fuel, SOPS, ............
The list is long. Welding subs, branched and subrogated claim, maintenance, etc. etc. The Room will be full.

AF

[sooty655]

In the case of the GE, where fuel icing is addressed in the design,


Not sure about your wording there, airfoilmod. I'm sure GE, RR and others all designed for the level of fuel icing anticipated/specified by Boeing.

If the GE arrangement really is better at accepting the unexpected quantities of ice dumped from the pipework, then that is luck, not design.

Two rollbacks over the entire 777 operation is a very small statistical sample. I'm not yet convinced this is only a RR problem.

Sooty

[airfoilmod]

The Icing of Fuel was explicitly shown in the schematic for GE. It was not shown on the schematic from the same source for RR. I mentioned that before, and meant only that, not that RR hadn't addressed the problem as understood at the time. The presence of three separate HX on GE may or may not be more effective, and your noting that only two rollbacks have been documented for the Trent is quite valid.

airfoil

[Sir Richard]

tanimbar

The 3C you quote is the required margin above freeze point, not an actual temperature.

With -47 fuel the minimum fuel inlet temperature would have to be -44 for RR engines.

Similarly GE could accept -47 and CFM -42 at the engine fuel inlet.

But perhaps you knew that already.....:confused:

[tanimbar]

Thanks for making clear the figures in that document that I mentioned.

But perhaps you knew that already...Not for sure. It was one possibility I identified from the words used in the document.

Thanks again.

[Mismatch]

...Weight, weight, weight...

Honestly, weight is really not a problem these days on commercil aircraft when we are talking of a few pounds, seriously.

Think of just a crew putting on a few pounds each, let alone big blokes Vs small blokes, or the whole pax... or just a gallon or two extra fuel - honestly, things are NOT that critical that it would come into a design engineer's decision when safety is an issue.
...

Some pounds here plus some pounds there make up for two-digit tons in the end. I am sure, weight IS an issue in aviation. And it may even be an issue WHERE it is.

[airfoilmod]

The prior ref. to weight involved a hypothetical increase for additional system design in the Trent. Specifically a bypass for Fuel around the FOHE. The Trent is already leaner by 2,600 lbs than its GE counterpart, so some room may exist for a contemplated addition of Plumbing. Of course weight is important. Safety frequently revolves around weight. Where it is, and how much there is.

AF

[HarryMann]

Thanks Airfoilmod for clarifying that.

Of course weight matters, but in context... if you had 1,000 similar linkpins or rivets holding something on, you would spend a lot more time optimising the design for size, weight, material and stress levels as well as on testing to assure your final release.

But if you have 2, one per elevator for instance, over-designing them by 50% wouldn't make a bat's hat of it, would it, and in fact, because being only two in a critical path, would probably require you to apply a larger proof/ultimate factor, a wider fatigue factor and for peace of mind, a larger Reserve Factor.

I've seen one or two rather crass and ultimately deadly results from not understanding or formally addressing a sensible weight/citicality balance... e.g. a single 7/32" shear pin might suffice and meet the design case, but one day fail, a 1/4" might never go anywhere near a failure mode. Weight difference approx. zero!

If an engine needs a by-pass around a heat exchanger, being on the C.G or close to it, even if it cost one pax, or two on MTOW, if it needs it - it needs it - FULL STOP

[barit1]

I am really surprised that Boeing let the R-R Triple7 out of the barn without very aggressive fuel heating capability. Boeing's experience with fuel icing goes back six decades - and they have a library full of lessons learned from B-47, B-52, 707 etc.

Look at 747 etc. fuel schematics and you'll see what I mean.

[sky9]

The relevant point about ETOPS is that twins fly about 4000ft higher than the equivalent 4 engined aircraft. That must mean lower fuel temperatures over the same flight time. Has anyone checked?

[punkalouver]

Boeing's experience with fuel icing goes back six decades - and they have a library full of lessons learned from B-47, B-52, 707 etc.



Any details would be appreciated.

[Green-dot]

Just to reflect on the ice theory. Last week I personally experienced something totally unrelated to this incident but then perhaps not.

While extracting some money from an ATM (automatic teller machine) my mobile phone was activated as someone made a call. At that exact moment I was logged into the machine and had punched in the first of 2 digits for the amount I wanted to extract (40 euro's) when the machine went berzerk. I never got to punching in the second digit or confirm the amount by pushing the "ok" button as it spontaneously returned my card and released 100 euro's.

I finished the call and then, confused, I made another extraction with the phone off and the ATM performed as advertised in a normal way.

The incident is now under investigation.

This brings me back to BA38 and how perhaps a one in a zillion chance of EMI/HIRF could have ended its carreer prematurely.

Green-dot

[vapilot2004]

The PM's antenna farm radiations coupled with a nattering nymph's Nintendo DS
in row 13 caused both metal-encased & shielded ECC units to go bananas.

Ice was a related factor as there was not enough in the mother's drink in row 13 so there was just enough added vodka to knock her out keeping the woman
from such maternal duties as slapping the wayward child on the noggin when
he continued playing the small electronic aircraft systems jammer otherwise
known as a portable video game.

[Green-dot]

The PM's antenna farm radiations coupled with a nattering nymph's Nintendo DS
in row 13 caused both metal-encased & shielded ECC units to go bananas.


When reporting the ATM anomaly to the bank I was met with the same cynical reaction. The reaction was that it was impossible radiation from a mobile phone could cause the ATM to fail. "It was just a matter of coincidence . . . . ."

At least I'll give credit to the AAIB as they did investigate the possibility of EMI/HIRF affecting BA38. Question remains though if all conditions at the time could ever have been duplicated and if all essential data was recorded. For now I will wait until the final report has been released.

Green-dot

[misd-agin]

Barit1 - I am really surprised that Boeing let the R-R Triple7 out of the barn without very aggressive fuel heating capability. Boeing's experience with fuel icing goes back six decades - and they have a library full of lessons learned from B-47, B-52, 707 etc.

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

Any chance Boeing and R-R had a difference of opinion, and R-R stated "our engineering says it's good enough, and you're just operating on opinion" ?

[Monom]

757 is my speciality and I know why, when on the walk-round, the left wing always pours water down the back of my collar whilst the right wing remains frosty. Is the 777 walk-round similar? Without going all the way through the thread, I would assume that wing tanks were in use at the time. If so, all a bit odd?
Monom

[Joetom]

Thought I read, Boeing purchased MMM, that 777 appears to be a tough old bird, great landing by the crew as well.

[Mmmayday38]

JoeTom wrote;
"Thought I read, Boeing purchased MMM, that 777 appears to be a tough old bird, great landing by the crew as well."

If Boeing did, then they bought it off the insurers and it was in small cut up sections!

[Will Fraser]

May I ask a pertinent question? Anybody still breathing at AAIB? Have they been redundantated?

[chris weston]

Will,

AAIB are still well within their averaged time frame.

Nothing sinister here.

I also believe (naively many will say, no pun intended) this thread actively informed AAIB of sensible possible lines of enquiry...........

All covered in great detail in earlier posts.

CW

[Will Fraser]

chris weston - Thanks, and I agree this thread was food for thought. No acknowledgments are necessary, nor will they be likely forthcoming. That is as it should be. Honestly, I think some of the boffins at AAIB might resent some of the comment here, I probably would. I did not mean to imply any suggestion of conspiracy or anything sinister, just trying to foment a comment; thanks again. Also, I would definitely include your comments on thread on my list of very constructive contributions.

[HeathrowAirport]

Just a quick question, but maybe irrelevant, but BAW38, BAW39 is now done by a 747, is this due to its lack of problems during cold flights that it does, and or that BAW38 crashed in a 777 its a Public relations issue that its been changed to a 744?

[Will Fraser]

Fewer problems flying cold? Public relations? Guess: both

What's Delta doing?

[wiggy]

Not a guess, an answer: Neither. Following the accident BA suddenly found itself a 777 short, so there was a change in Fleet utilisation and a 747 was slotted in.

BA continues to operate 777's on Shangai-London, an equally 'cold route' using Chinese fuel. It's also going to be using the 777 on one of it's HKG services this Summer ( which often routes home via overhead Beijing and then onwards via Siberia), and there is the possibility of BA using 777s on NRT this Winter......not exactly the warmest of routes either.

[HeathrowAirport]

Ah thanks for that Information, but would also PR also be included, I wouldnt as a CEO even if it meant reducing pax vs fuel burn, a 777 operating a route that it crashed on.

[wiggy]

In all honesty most passengers are completely unaware and are utterly disinterested in what aircraft they are flying in, and don't know a 777 from a 747 from a 737.........

[Will Fraser]

HeathrowAirport -

Don't discount the effects of #engines. I have seen plenty of pax count them on their fingers before boarding. I'd like to encourage you to continue to ask good questions, stay objective, and don't take casual commentary to the Bank. When ETOPS was proposed, a healthy percentage of pilots were questioning the format, some still do.

Don't allow your questions to be dismissed out of hand, certainly not on the Internet.

Having said that, there is no reason whatever to mistrust ETOPS. Make up your own mind.

Will

[Williams2353]

What's Delta doing?
They are still flying their 777LRs between Atlanta and Shanghai, Seoul and Tokyo.

And I am here to verify that at least this one passenger does indeed know what type of aircraft I fly, and is keenly interested in a final fix to this problem, beyond operational work-arounds to unclog the ice from the heat exchanger tube sheet. The 777 is my most frequently flown airframe (I keep a log).

Edit: I meant 777ERs, not LRs. The LRs have different engines and are used on other routes.

[wiggy]

I reckon you're probably the exception that proves the rule...:ok:

[HeathrowAirport]

Actually, would anyone kindly be able to show me the loads for BAW38 pre the crash and after, even though this would be biased due aircraft size. Whats the loads?

And Will Thanks, I prefer the 777 to the 744, dont take offence, but since that crash Ive liked the 777.

[gtf]

Available at http://www.aaib.gov.uk/cms_resources/Interim%20Report%202%20-%20%20G-YMMM.pdf

[Pinkman]

This is essentially a refinement of interim report 1, tidying up some rough experiments. It's easy to criticize the slow progress but it's really difficult to simulate - think of the early wind tunnels.

At the end of the day, there needs to be a dedicated interagency fuel research centre to physically model these issues accurately, using a combination of actual engines and actual fuel systems in environmental test chambers (imagine!) and maybe even including extended duration high altitude flight testing. Irrespective of the current case, this kind of facility will anyway increasingly be needed when biomass derived fuels start to penetrate the market.

We need to get to the same level of sophistication with fuel testing as we are with blade containment. If you have never seen it its worth watching:

YouTube - Blade Containment (http://www.youtube.com/watch?v=-jVNRQyoAsc)

Pinkman

[Will Fraser]

Some questions then. As a fuel guy, do you conclude that the (permitted) water was the culprit? Was it an accumulation of atmospheric moisture via venting? What about the conclusion that the ice was 'soft' and 'malleable'.

Also, Pinkman, what of Boeing's 60 years experience of turbo (fan) jet performance at levels up to 60k and above? It remains disconcerting to me, probably to others that the industry seems to be a bit coy with the purported 'mystery' of this event.

What about the 'slurry' theory from Airfoilmod? Some combination of waxy fuel and microcrystalline water-ice? Have you seen this before?

[Pinkman]

As a fuel guy, do you conclude that the (permitted) water was the culprit? Was it an accumulation of atmospheric moisture via venting? What about the conclusion that the ice was 'soft' and 'malleable'.

Also, Pinkman, what of Boeing's 60 years experience of turbo (fan) jet performance at levels up to 60k and above? It remains disconcerting to me, probably to others that the industry seems to be a bit coy with the purported 'mystery' of this event.

What about the 'slurry' theory from Airfoilmod? Some combination of waxy fuel and microcrystalline water-ice? Have you seen this before?

Tough questions. I don't have an answer for all of them. All I can tell you is what I think which is:

- I think that the dissolved water is a complete red herring. Free water, eg from fuel stratification, may not be. And if that came from the free water then maybe the free water is an issue after all.
- I don't think industry is being coy: they just dont know what is going on.
- I think airfoilmod is very close. I believe it was a unique situation related to the distillation properties of the fuel such that it met all the ASTM tests but didnt perform as conventional fuel under those unusual circumstances. Who knows, it might be related to biofuels. Yes, I have seen distillate fuels wax up and I have seen an ice-wax emulsion.

The thing about fuels testing is that you only test for the basic properties (freeze point, smoke point, distillation range, Calorific value, etc etc) and the qualities of the things you expect to be there. In the UK we had a gasoline contamination problem a few years ago that took thousands of vehicles off the road almost overnight. The fuel met all the BS/EN228 spec tests. It took nearly a fortnight for someone to trace the fact that the fuel had been adulterated with waste electrical solvent (mostly toluene). It got the Octane rating up (its aromatic) but had silicon in it which poisoned the oxygen sensor. But it was on spec!

Another example: Chinese baby milk scandal. It contained Melamine, which tests out as a protein, but is of no nutritional value and actually harmful. But it was on spec!

The point being that you dont test for the things you dont expect to be there. Fuels are heterogeneous things that dont always do what you expect. In the short term the only way to get on top of this is to test them in the environment in which they will be used and use the information to modify the testing regime.

Pinkman

[phil gollin]

Still not madly keen on the interim report.

They still used the "wrong" fuel condition (90 not 70 ppm water) in the tests (for the perfectly valid reason that that is the industry standard so it would give results against POSSIBLE future failures) and they still didn't get the results that occured on the day of the accident.

The point about the water content being very variable (possibly due to ice freezing and melting) and difficult to measure is a serious issue. One glaring question is what end conditions they would have expected (in real life the water sample taken was 40 ppm).

So the tests are still first steps NOT a "smoking gun".

I am still disurbed that they are only concentrating on the B777/Trent combination and not extending the research, although of course there are the other recommendations.

I am a little concerned that the reports are looking too narrowly at the problem.

.

[Pinkman]

Couldnt agree more, and actually while you wrote that I was editing my earlier post to reflect that.

[Rightbase]

it has not been possible, due to limitations in the available recorded data, to totally eliminate the possibility that a fuel restriction, from ice, formed elsewhere in the fuel system which, in addition to an FOHE restriction, contributed to the engine roll backs on G‐YMMM. It should be noted that extensive testing and data analysis has not identified any features elsewhere in the aircraft fuel system which would have caused a large enough concentration of ice to accumulate and cause a restriction.The report refers earlier (p7) to the possibility of water accumulating during the flight rather than being ingested with the fuel burned some of the water settled and froze on the bottom of the fuel tank.
and on page 8 to the effect of water injected into the fuel flow.

It seems to me that there is a serious possibility that at warmer levels, ice which has accumulated in the centre tank will melt, allowing the fuel scavenge pumps to feed it into the (still cold) main tanks, where on its way down to the boost pump inlets it will freeze. If the centre tank melt water is suddenly presented to the scavenge inlets, by a decelleration or a change of attitude, it will result in a significant temporary production of ice in the main tanks.

[maynardGkeynes]

That cavitation was present is interesting, but not dispositive, unless it is so unlikely to be found on other aircraft of this configuration that it almost certainly points to icing as a cause. Suppose the AAIB examined other RR 777s. What percent would be found to have cavitation of this pattern? If the answer is lots, the causal connection is less established. And as a factual matter, have they done this?

If this has been answered already, I apologize. Please refer me to the post # addressing my question.

[Pinkman]

Yes, thats what I mean when I, and many others, have referred to "fuel stratification". All you need is liquids of different densities and suitable environmental conditions. In the pub, you can get whisky to float on water if you are careful.

[Pinkman]

I thought this was interesting - on the web:

https://www.totalga.com/document/FAME%20Bulletin.pdf

and the attachment to it ( NE-09-25 ).

The industry has obviously recognized the issue and are taking steps to address it. If the AAIB hasnt yet positively discounted this by doing the GC-MS analysis to rule out FAME contamination then they need to. If they have, then they should say so.

[Will Fraser]

Pinkman

Bear with me. Some questions. If the industry is lobbying for 100ppm that's more than dissolved water, and the problem there is patent (038)

Are the producers trying to keep their fuels "on test" by introducing and regulating a substance heretofore not allowed in any fuels test?

My concern is the fat itself. Organic fats have in the past been used as

1. Glue

2. Thickeners

3. Coatings (Varnish)

4. Resinous molded parts (phenolics, phthallates) etc.

The potential for disaster is apparent. Are they trying to put these substances in jet fuel, or defending their possible presence in jet because of an inability to keep separate the biodiesel from jet in mixed transport, and production processes? What is it?

[Pinkman]

Will

I couldnt possibly comment except to say that its a contaminant, nothing more, and it arises from the tendency of the product to stick to the sides of the pipeline and contaminate other products. Its called tailing. You have to have multiproduct pipelines because you simply cannot have dedicated lines for every product... or that was the thinking until now.

I am seeing a lot of activity to devise safeguards against this, but that wasnt the point of my post, which was to look possible relevance to BA 038. The thing that has always puzzled me is that, while within the normal Jet A-1 spec (-47 C), the FP of the fuel when analysed was actually much less than typical RP-3 which I understood to be in the minus fifties. I was trying to work out whether this is consistent with FAME contamination. I havent reached a conclusion.

[Will Fraser]

A long ago post by airfoilmod comes to mind. He took issue with the 'in spec' conclusion of AAIB testing, though the FP was markedly lower than standard Minimum. His position was something like "Where does 'meets and/or exceeds' come into play relative to 'in spec.' Does the authority accept the unusual characteristic (low FP) as long as the 'miminum' is met without questioning the mechanism for the drastic difference?

I don't think he ever got an answer.

[Pinkman]

He got an answer from me. I said he was talking rubbish. I may yet have to apologize - seems like he was way ahead of me. To be fair, I was thinking more along the lines that the aviation Kerosene produced in that region probably had more than one use (eg for military as well as commercial) so if it exceeded (bettered) the commercial spec by such a wide margin, so what, as long as it comfortably met Jet A-1 norms. Which, on the face of it, it did.

[lomapaseo]

I would be cautious about the interchangeable use of the terms meets or exceeds in a complex substance or system. Whether its a hydro-carbon or a composite structure, its the balance that's important. The spec is based on the knowledge that in balance (meets) it works. Change something (an ingredient or structural stiffness) and you no longer can be sure that it will perform acceptly in the common situations like it did before.

The assumption is that the product has been analyized/tested with variations within the acceptable range of "meets"

[Will Fraser]

That was exactly the point, it seemed that 'meets' and or 'exceeds' the spec. satisfied the authority. Should it have? In my opinion, NO. What is it about such a low FP that should be investigated?

E.G. What temperature is boiling water? Where on the Planet is one?

[Oilandgasman]

Made Jet-A1 for 14 years.
There were 66 samples of fuel drawn from this aircraft after the accident and the AAIB have reported that no contaminants were found other than traces of water. Chinese N03 Jet Fuel complies with the Spec for Jet-A1. In order for JetA1 to meet spec it has to pass 38 tests. If organic fats were present they would have been detected in at least three or four of the tests.
Some of the tests, e.g. density, are set with pass rates between upper and lower limits. If the results fall between the values then the spec for that test is met. Other results have to meet maximum or minimum values e.g. Flast point or Freeze point, if these minimum values are met or exceeded then the test is a pass.
When fuels exceed the values set then the quality of the fuel is not impaired.( The fuel producer just wastes money in the fuel production as they get the same price for it whether is meets or exceeds the spec. In my experience we played safe with Jet A-1 and never tried to be clever achieving a perfect blend, it was almost always better than spec.) In order to meet all the spec requirements some of the results will exceed the spec and this will vary from batch to batch. The Certificate of Quality is only issued if all tests have met or exceeded the minimum requirements.
Jet 1 is stored in tanks, pumped and transfered in it own dedicated pipework and was not in my days physically connected to any other pipework. Even drain valves had lead seals on them to demonstrate to an Inspector that the Jet A-1 containment system had not been disturbed. The seals were numbered with the refinery inspector's number on one side and a Government seal on the other. The small number of people who could fit these seals were registered and issued with their own seal compression tongs
The problem here is the management of water in an aircraft/ engine combination which was susceptable to any ice formation at low temperatures. There did not seem to be any fuel temperature control, the pilot got what the airframe produced in the climate in which he flew.The unlagged/non heat-traced pipe run from the fuel header out to the exposed FOHE and back to the engine being a cold section of the fuel system under discussion. The first time I saw the FOHE inlet tube
sheet I mistook it for a filter screen. I await the modifications to this system with interest. Like many of you I do feel it seems a long time coming. The final report? I am happy to wait for this.

[sooty655]

Jet 1 is stored in tanks, pumped and transfered in it own dedicated pipework and was not in my days physically connected to any other pipework.

I was also in the industry for a number of years (outside the UK). Where I worked, the Jet-A1 was kept totally separate from the other products within the refinery, but was transfered to the distribution centre via a multi-product pipeline.

Pinkman's concerns about possible contamination could certainly have applied there.

[Oilandgasman]

Good point Sooty655. If multi product pipeline was used then the Distributor has the responsibility to re-test on receipt and issue the appropriate Certificate of Quality before delivery to the end user. I am asuming that these products were separated by pigs. Having used these for years I do not have any confidence that there would be no leakage past them. My own opinion is that Jet A-1 is not really suitable for multi pipeline use. If the multi pipeline deliveries did not use pigs and relied on Operator intervention to separate the fluids on receipt then Pinkman is right to be concerned.
Another problem area is Jet A-1 delivered by ship. I have yet to receive liquids from a Super Tanker or Coaster which did not contain water. We obviously drained this water away on receipt but another source of water contamination if the onshore guys are not switched on. The quality control inspector, either way, is still responsible for delivery of non contaminated Jet A-1.
In the offshore business we still check each fuel delivery to a chopper for water. I have even had a RN pilot asking my Helideck Landing officer why he was holding a syringe up to the cockpit window. When the HLO told him he said they never bothered their Jet A-1 was always water free!!!

[Pinkman]

Hi Oil & Gas man... yes, I'm ex-refinery too. Multi-product pipelines are the norm nowadays in many countries, even for jet. I think that what the non-oilheads have to realize though is that the levels of FAME that can cause a problem are in the parts per million range. There is no field test yet (maybe next year) for FAME: at the moment specialized Gas Chromatography/mass spectrometry is the only way to be certain. There is no re-test done at the airport for FAME after transit, and none of the standard ASTM tests detect FAME (eg D-1655). The only way to be sure is to downgrade the interface slug and then some. There were some trials at CDG last year and it was astounding to me the amount of Jet that had to be downgraded before it was classed as "clean". I still think that AAIB should state whether they tested for FAME or not.

Its all very well saying "we didnt find any contaminants" but if there's a contaminant you were not expecting, you wouldnt test for it, would you, so how would you know?

If organic fats were present they would have been detected in at least three or four of the tests.


See, thats the bit that really worries me because back last year there was only one test for FAME (GC/MS) so I know - bein' a kemmist an' all - that we are not looking at the same test. If the Chevron letter is correct and that even now there is only a handful of labs that can test for FAME at the moment, which of these "handful" were the 66 fuel samples sent to?

[Will Fraser]

Question? Would Fatty acid methyl ester be a danger at any level? With its sticky propensity, wouldn't 1ppm be too much? Seems to me 038 fuel testing results entertained that 70ppm water was cumulative, and could be a problem regardless the presence or not of atmospheric moisture or lack of sumping over time? I recall they pointed out that even very small amounts of water was a problem, because so little was known of fuel performance at very low temps due to ETOPS, etc.?

Is the industry then actually trying to allow some amount of this contaminant in the test simply because it "is too expensive to maintain isolated piping and production storage"??

[GemDeveloper]

But...

My understanding is that FAME is a component used in automotive gas oil (diesel), in markets where there is, for whatever reason, a need to use renewables.

Pinkman and others are quite right about multi-product pipelines, and I know that there are all sorts of concerns about aviation fuels passing thus, particularly where there are fuels containing renewable components passing along the same line; even if it's pigged, as pointed out, the piggies are not fool- (or leak-), proof.

And the but is... does anyone know if there is any likelihood that the Chinese market is using renewable components in their diesel or other fuels? I'd have guessed not, but it's a while since I have been there, and the one thing that one can say about China is that change is rapid... or, was there a period when the fuel supplied at Beijing was from an 'unusual' source (perhaps cargoes brought in by sea), and there might have been contamination from such a component introduced, e.g., from a product tanker?

[Pinkman]

GemDeveloper

Thats the $64K question. China does use biodiesel but until recently it was primarily a bioethanol market. In 2006 it was the third largest producer of bioethanol in the world.

Will

I realize I wont convince you that the industry isnt trying to "get away" with leaving the maximum amount on FAME in Jet. But the fact is that every critical aviation activity is subject to a balance of risk and cost with an adequate safety margin thrown in. A main spar is designed as a trade off considering weight, design strength, manufacturing techniques etc. Fuels are no different. For airlines, fuel as an input cost has gone from 13% to 40% in seven years. The Jet demand has gone up by two and a half times since the 1970's. There is no way the latter can be sustained without using MPP's without also making the former even worse. Dedicated lines are not an option and MPPs are here to stay. However avoiding FAME contamination means that 50% extra buffer volumes of Jet have to be "thrown away" (transmix volumes sent for reprocessing) to ensure "FAME free Jet" (<5ppm). This extra cost is of course reflected in the cost of the fuel. Yet 5ppm is actually arbitrary, because its currently set at the level of detection. There is currently no agreement on at what level FAME becomes an issue in Jet although some say 400ppm. Changing the specification to a more practical limit gives two advantages: firstly it gives the airlines a break on costs. Secondly, it becomes possible to develop a field test that can be used at that lower level of sensitivity without having to have a PhD analytical Chemist at each airport. The trick is to establish the balance of cost and risk in the right place. And that hasn't happened yet.

[RomeoTangoFoxtrotMike]

Airworthiness Directive for replacement of FOHE issued here: EASA Airworthiness Directives (http://ad.easa.europa.eu/ad/2009-0142)

[Pinkman]

Excellent solution. Now, remind me, what was the problem that was definitively replicated?

[Will Fraser]

I have been reviewing this thread for several hours. I found this post amongst others, but it has a premonition I thought interesting.

15 May 2008 #1151 (page 58)

Will


Pinkman Not so 'excellent' Eh? If the new FOHE is a fuel heater as well as an oil cooler, (as the original part is not), not so bad, but.......

[Pinkman]

My understanding is that the problem is yet to be replicated. If it is AFM's theory of accretion of solids at low temperature followed by blockage on demand then the mod will clearly help. But I find it extraordinary how someone can propose and start to implement a solution - especially one costing presumably a huge amount of money - in the absence of a clear problem definition.

How very British.

"Dammit man - don't just stand there! Do something! Anything!"

[RomeoTangoFoxtrotMike]

But I find it extraordinary how someone can propose and start to implement a solution - especially one costing presumably a huge amount of money - in the absence of a clear problem definition.

How very British.

"Dammit man - don't just stand there! Do something! Anything!"

Not so much British, more "international politician". See:- Politician's syllogism (http://en.wikipedia.org/wiki/Politician's_syllogism) :ok:

:suspect:

[Pinkman]

Excellent! :}

[Will Fraser]

Nearly eighteen months on, the "solution" appears to be "melting the ice"?

Bravo ? Arse about. Why not keep the ice out of the fuel, after FIRST addressing that as the problem itself. "Previously unknown characteristics of fuel at very low temperatures?" Using an oil cooler to melt ICE that is NOT supposed to be present in the first place? For a pilot, any one peeping the pictures of ice clogged fuel lines, reading the "AD" has to be perplexing.

Pinkman, taking note of the ice build up, do you conclude the ice derives from "in spec" fuel giving up its soluble water content in long duration cruise to block crucial lines at the engine? Because that's where I am. In your experience, isn't a simpler explanation poor fuel handling? As in, tanking, sumping, pumping, storing, etc.? Is it really the Trent or are other installs vulnerable?

As AFM said, "It's the Fuel".

[sooty655]

Is it really the Trent or are other installs vulnerable?


Will,

See my post 2443. It is only the Trent based on a tiny sample of three engine rollbacks on two flights. No-one knows how many times other power plants have been hit with enough ice to almost (but not quite) cause problems.

Watch this space.

Sooty

[Will Fraser]

So much of what we see from the authority seems to depend on blind faith. A "tiny sample" can NOT be relied upon to exclude a growing and more pervasive problem. It is shortsighted to assume it is only Trent, based on information in the public domain. It is as you say, sooty.

Without a complete audit of every possibility, this AD rings hollow. A "Patch". An expensive patch, but a patch nonetheless.

Will

[lomapaseo]

See my post 2443. It is only the Trent based on a tiny sample of three engine rollbacks on two flights. No-one knows how many times other power plants have been hit with enough ice to almost (but not quite) cause problems.

Watch this space.

Sooty

Agree:ok:

reminds me of the uncommanded thrust reverser problem. A Boeing specified, requirement but at first unique to only some PW models. An AD appropriately addressed the known. Then more data arrived (Airbus, Douglas, RR, GE) and additional ADs addressing the knowns in a specific fashion.

So I'll watch this space :) for additional knowns that can be addressed in a specific fashion.

Some may feel that this is guessing at the location of the bullet in the chamber, but then again throwing a design change at something that currently works just adds more bullets.

[Will Fraser]

The FOHE (Trent) was not specifically designed as a fuel heater/ice melter.

I can't stress this enough. Modifying an existing component to mitigate a problem its overall design was never meant to address is unusual, to say the least. In the absence of further work on fuel/fueling issues, (is there any?), the actual cause of the icing induced rollbacks is being neglected?

The ICE is not the cause, it is what causes the ICE.

[falconer1]

100+ on that...

wonder, whether that situation IS in fact causing some nailbiting, especially in regards to the ultra ETOPS qualification of the B777..??

not that a common denominator like water / ice contaminated fuel ( for whatever reasons, i.e bad supplier quality and/or bad draining routines, sometimes caused by that fact that during the short downtimes of long range flights you cannot possibly drain all condensation out etc etc) could not down a quad either, BUT the statistical probabilities for a twin to be affected on both motors would be considerably more severe..

so, anybody know?? were there any discussions to at least consider temp withdrawal of ETOPS qualifications????

dont get me wrong, still very impressed with the 777 in general, but that accident shook me up a bit...

and it may point to a far wider reaching problem, and that is fuel quality in general..and maybe insufficient means to get the water out of it..

and that again may not have much to do with the type of aircraft..

[Pinkman]

Pinkman, taking note of the ice build up, do you conclude the ice derives from "in spec" fuel giving up its soluble water content in long duration cruise to block crucial lines at the engine? Because that's where I am. In your experience, isn't a simpler explanation poor fuel handling? As in, tanking, sumping, pumping, storing, etc.? Is it really the Trent or are other installs vulnerable?


Will, As a fuel guy, this is the way I see it:
They cant use the fuel recovered from the aircraft (would be gone very quickly) but they have tried VERY HARD to bung as much water as possible into the test fuel and STILL they have not been able to replicate the fault although they have seen icing. So while I still believe it was fuel related I havent seen anything yet that leads me to believe it was simply water in fuel. I want to know why the fuel FP was elevated over typical RP-3 even though it met the spec for Jet A-1. Do I believe the Trent before the mod was more susceptible? Yes. Do I think that other powerplants would suffer the same problems as the environmental conditions became more severe? Of course.

Regarding your question on handling, it doesnt really matter - if the fuel was on spec and was badly handled and became unfit for purpose despite being on-spec it is no different to it being unfit for purpose and well handled.

Cast your mind back to the Australian avgas incident which caused a plane to fall out of the sky and grounded the Victoria GA fleet. Trace amounts (parts per billion) of Di Ethyl Amine - a chemical that is used widely in refining to remove Sulfur, and something you wouldnt expect to be an issue - caused a wierd reaction with the metal piping / braze in some aircraft fuel lines. The fuel met spec. In this sort of incident it is simply not enough to say "the fuel met Defstan 91-91" or whatever. You have to take it apart molecule by molecule and look for things that you "dont know that you don't know".

[vapilot2004]

Nearly eighteen months on, the "solution" appears to be "melting the ice"?

The fix is not melting the ice as much as it is mitigating ice on the move, en masse. According to what I've heard, the FOHE design has been modified for reasons of flow, not heat transfer.

Reliable fuel delivery is something we should have mastered by now. Perhaps after the introduction of new fuel formulations, certification was not thorough enough on this particular aircraft and engine combination.

[Will Fraser]

vapilot2004

To now, the fix is an operational workaround, a cycling of thrust to heat the engine, melting the Ice.

Until AD compliance, that is the 'fix'.

After fleet wide compliance, a combination of operational and mechanical defense against Ice? There is an assumption here that Trent/777 is an isolated example of inability to resist ICE in FUEL. Absent a broader approach, it has all the appearance of a 'Patch'. The passage of time dulls some of the attention paid to this problem.

Given the nature of design, the workaround will have what effective measure of performance? Unknown, is my guess. Until the Fuel is understood better.

Will

[vapilot2004]

Will,

I think the interim recommendation addressed two areas of concern. The power increases not only add heat to the FOHE but also cause the fuel flow to increase dramatically above idle rates, forcing accretions to break up and move on down the pipe.

My comment earlier was referencing the Trent's new FOHEs, so I may have mis-quoted your meaning. Apologies. :8

I agree that there is something odd about what has happened here and once again am left wondering out loud how this could have been missed by Boeing, Rolls and the regulatory bodies during certification. I think something changed and it smells like kerosene to me.

[Will Fraser]

I haven't smelled Chinese Fuel from China. What drops an FP 20 degrees below 'spec'. If its expensive, why bother ? If it's cheaper, why ?

[chris weston]

Will,

You can lower the FPt (i) by branching the hydrocarbon chain (use more of a catalytically cracked high Mr feed stock) or (ii) by shortening the chain length (use more of a more petrol/naptha like cut). Its a Van der Waals / London dispersion forces argument.

I would guess that either of these routes would push up costs but the fuel guys will answer that better than I can, I'm just a chemist....and yes yes I appreciate the possible use of (non hydrocarbon) additives.

CW

[Pinkman]

Would be interesting to take a sample of RP 3 / JF #3 NOW and compare with the recovered sample via GC MS as well as distillation range... and scouting for all those ex-PEK retention samples that will be hanging around from the last 5 years. There are only a few general possibilities for lowering the FP and they include, firstly, changes in the relative proportion of hydrocarbon components that SHOULD be there (eg wider than normal wide cut fuel) and secondly, the addition, either deliberately or accidentally, of hydrocarbon components that SHOULDNT be there (e.g. FAME). Then of course, there's the non - hydrocarbon components.

It would help if we knew which tests were done. If the material was on spec, what is the harm in releasing the data?

[Mariner9]

FAME can't improve FP in Jet, and is of course tested for nowadays in the standard spec.

Pinkman, I know you keep harping on about GCMS but do you really think it wasn't done? I agree however that there would have been no harm in releasing the data or even add a simple line to the report that nothing unusual was noted on the GCMS profile.

Personally, I would be interested in a comparison of profiles between the fuel samples from the aircraft and the retention samples. A "depressed" FP (if it was in fact depressed) for the aircraft fuel could have arisen from a reduction in the heavy HC components present (wax dropout? - though no wax deposition was apparently found doesn't mean it didn't happen)

M9 (who investigates Jet A-1 contaminations for a living)

[sky9]

Are we all not in danger of "examining the molecules" while forgetting the big picture.

What needs to be done to avoid the engine stopping again? The FOHE is not a fuel heater but an oil cooler and is designed as such. Presumably the engine is capable of taking a reasonable amount of water or ice in the fuel so does the revised FOHE allow slush ice to go through if not should there be a by-pass?

[chris weston]

In common with many others, I've read every post made on this venerable and informative thread and it’s good to see their quality and thought-provoking nature being maintained. (Until this one…….)

The issue of bypassing the FOHE has been covered in detail already. If memory serves, one contributor, presumably with tongue firmly in cheek, even claimed a pat pending on his particular solution.

But I'm with you sky9, how can we actually deal with the rollback problem is the key. As we don't know what the problem actually is, that makes things really tough.

Presumably the question is how much ice in the injectors can be handled before blockage and presumably flameout never mind rollback, occurs?

I have the greatest of respect for the quality of the engineers working for RR and I'm quite sure that this will already have been looked at exhaustively by RR. I'm also naïve enough to take on trust that if it was just a matter of putting in a simple bypass system, RR would've done it long ago.

CW

[Will Fraser]

chris

I have no naive trust, at least not relative to that which I had years ago.
I think a 'simple bypass system', may have been looked at prior to original design vis a vis Trent8, but frankly, I think it is being actively avoided at this point. Retro isn't simple, it isn't cheap, and it isn't logistically benign to any of the principals.

As read, the AD focuses solely on the FOHE. airfoil was the first to point out its design purpose did not include Fuel heating. If it did, Oil would not bypass its chamber as a designed mechanism (oil bypasses now only when it itself does not need cooling). This also raises questions about your faith in an a priori engineered look-see at the potential for Fuel Ice.

Since there is no provision for Fuel supply to the powerplants if for any reason the FOHE is clogged, one doubts the thoroughness of the investigation for potential Fuel starvation due to such a problem.

One could make the compelling claim that in the absence of an alternate path for fuel bypassing the FOHE, the sacrifice of FLOW (fuel) was not deemed to present a critical path, ipso facto; there was a determination made to exclude such a safety implementation. To think that it was excluded by accident, is beyond even my cynical approach and suggests our shared faith in the engineering, though from different perspectives.

Will

[Smilin_Ed]

Chris:
As we don't know what the problem actually is, that makes things really tough.I'm not being facetious here, but we really do know what the problem is/was. In it's simplest form, some of the "stuff" in the fuel tank froze and blocked path of the fuel to the engines. There may well be a number of scenarios in which this could happen so what we have to do is to prevent freezing during all of them. That means heating the fuel near the in-tank pumps. Is there a source of heat, now wasted, that could be put to good use?

Will, I share your concern about the cost of retro-fitting a change like I propose above, but how does that compare to the cost of losing a plane, not to mention crew and passengers? Fortunately, this time it was only the plane.

[Will Fraser]

Smilin'Ed

You may have missed the irony in my post, I suggested that a retrofit of a full on bypass for fuel was being actively avoided.

If you think something more than 'converting' a cooler to a heater is necessary here, we are in complete agreement. I also agree with the conclusion that we know precisely what happened to 038 and Delta. The 'mystery' of 'unknown' characteristics of Fuel is a dodge, simply put.

Will

[chris weston]

Will, Ed, thank you both.

I very much take the point that we know that it was solid phase water that triggered the roll back, my point was a little wider and not well made.

Without going over old ground too much and with due caveats ........

What we don't know is why, if the fuel was shall we say "well within spec" (neutral language) and the flight path and temperature profile not that statistically unusual, the problem has not occurred in something close to this form in many other flights too.

After all I've read, I'm still mostly in the "it's the fuel" camp. Was it made right, was it handled right, was the water drainage right etc ad nauseum.

CW

[Cloud1]

Question - has BA or Boeing changed anything on the B777 to avoid this happening again? I will be honest, I have not read through the 125+ pages to see if this has been answered so apologies, but hopefully someone will either be able to say yes or no. :ok:

[lomapaseo]

Cloud1

The answer is yes the details are all in the thread including the past week.