It almost makes one wonder if insertion of random, minor, marginal measurement and specification errors throughout a precision construction process would be desirable (thinking again back to the airway precision debate where random lateral offset - though still within the airway - is in current thinking).

I hastily add that I should probably patent this idea.

Re-Heat,
You may have a point.....

Remember the static test on the A380 wing that broke at something like 148% of design load, rather than 150%?

Maybe, sometimes you would like to have that little bit of extra margin, because they did not mill out every single "superfluous" ounce...

Might be worth discussing, although it's more academic than anything else.
Accidents due to this kind of extremely rare combinations of circumstances still happen, agreed.

But as long as third-world airlines dump badly maintained aircraft in atrocious circumstances with a frightening regularity.... I think our priorities are elsewhere.

Post #251 and #254
 

Having to do with mirrored and duplicative systems (Fuel). has been addressed elsewhere also. In perfecting more and more dependable systems, the Human side of the equal sign becomes more and more..... Dependent. ETOPS must for purposes of economic feasibility, divert from isolation and engineered anomalous design to make more and more infrequent, the failures which challenge the philosophy. There is a definite difference between redundancy and anomalous isolation. Redundancy merely provides two systems to fail under similar circumstances; heterogeneous engineering separates the systems in ways that "prevent" mirrored fault.

Airfoil to Re-Heat: it's called engineered anomalous design.

As I offered before, 038 isn't about Etops, instead its about vulnerability of separate and equal systems.

trashie:
propaganda:
CONF iture:
barit1:
I assume trashie is referring to the boost pumps, not FADEC or HP pumps. If so, the pumps themselves are outside the hull (which functions as a Faraday cage) and very unlikely to have been affected.

Regarding the (pumps) electronic component locations relative to the mentioned seating position of the "official with his laptop", he would have been nowhere near any of those components if you know the T7 well enough.

Suppose the pumps were affected (highly unlikely), what effect could there have been? Stop the pumps? Suction feed would still feed the engines. Or make the pumps (3 phase AC) somehow run in a reverse direction . . . .and then all four of them at the same time with their LH/RH electrical circuits well separated? Again, highly unlikely.

If there is any substantiation in what the accident investigator discussed, the scenario could fit uncommanded transit of both spar valves. More holes in the swiss cheese had to have lined up though before such a scenario with a laptop could be considered as plausible.


Regards,
Green-dot

The loud laughter and hilarious applause following this "revelation" have been edited from the tape in question.

pls8xx

Keep up! Just to clarify the 777 fuel system, there are two booster pumps each with a non return valve located at the rear of each left and right wing tank. Each pair of pumps delivers fuel independently (unless the cross feed valves are opened) to its respective engine each of which is fitted with a heat exchanger and each with a mechanically driven HP pump.

Flight Safety

Your experience with the shower is a perfect analogy to the effect I have described.

The booster pumps are centrifugal and will operate constantly at their rated speed even when no fuel is actually being consumed as will happen for example during the initial stage of engine starting. As the resistance to flow is decreased, the volume of delivery will increase and the delivery pressure decrease accordingly. (A graph indicting values is on the catalogue for those interested).

The HP pump has to be a positive displacement pump – for example a vane or gear pump – such devices being able to produce the much higher pressures required for the burners. Regardless of the boosters trying to always deliver their maximum possible output, the HP pump will only allow a fixed amount of fuel to pass for each shaft revolution, the rotational speed being determined by its mechanical connection to the engine. It is this then that offers the restriction to flow that permits the build up of pressure fluctuations having the effect in this circumstance of being a valve that is opened or closed against the delivery from the booster pumps in accordance with the engine fuel demand.

Although it does not affect the resonance scenario, the HP pump is also fitted with a bypass arrangement. By this, the pump will always be delivering too much fuel for any given engine speed, the excess being recirculated in the vicinity of the pump. This also allows the pump to pressurise the engine fuel system against the closed fuel valve during the start procedure when the pump has no option to rotate with the engine although no fuel delivery to the burners is yet required.

Ailfoilmod

Enjoying your mind stretching additions. I keep reflecting on the possible pressure waves and other dynamics that might have been dancing together in the remaining bulk of fuel in those drum like fuel tanks…

Re-Heat

Exploring this incident - among others - I also have many thoughts about the relevance of precision on safety. It remains for me that if we were really meant to fly our bodies would be formed with wings, a tailplane and something hopefully more akin to a Merlin than a flat Lycoming between our legs. Having a personal lack of such equipment, given the choice, I think I would anyway still tend to choose the safety of today’s imperfect machines over too many adventures being carried aloft in the likes of the Doves and Herons of my youth. The fallibility of the human controller(s) nevertheless probably remains a greater threat than the fallible machine.

Regards
JG

3 Fuel Pumps per Engine
 

1. Low Pressure boost pump in wing tank, output is "constant"
2. Low Pressure - engine driven, output is direct relationship to engine rpm
3. High Pressure - engine driven, output is direct relationship to engine rpm


http://img83.imageshack.us/img83/817...pw3bww3.th.jpg


http://img75.imageshack.us/img75/308...ug1bli7.th.jpg

Low inlet pressure to the HP pumps is a focus of the investigation. There's a lot of cheese slices between the fuel tanks and HP pumps!

Harmonics? Perhaps.

Beyond FCOC and fuel tubing atheromata, I'm suspicious of excessive Prerotation and Backflow of unusually cold & viscous fuel reducing output of all the low pressure pumps.

An increase of intake vortices at the wing tank boost pumps may have been exacerbated by relative fuel surface level changes in relation to the pickups due to aircraft pitch changes during approach.

http://caltechbook.library.caltech.e...igs/fig408.jpg

http://caltechbook.library.caltech.e...igs/fig406.gif

-=MachacA=-

I wouldn't suggest a return to past, inherently dangerous designs would be desirable!

The simplest explanation
 

might involve the HP packing viscous fuel into the nozzle annulus and/or the bypass (relief circuit) while the Low side simply couldn't keep up. At this point the fact that the LP's were active would RESTRICT free flow, the alternative of suction being locked out. At some location (bearings at high side) is where the Fuel "Sheared" into dense "petals" and "voids" (cavitation). Alone, I think cavitation was insufficient to choke the supply, but briefly. At this point (when the Engines were ~1.57 EPR), I believe the coup de grace may have been introduced into the supply with an as yet undetermined combination of Resonance, Harmonics, flutter (at LP valves), and an inability of the system to "select" suction or boost. The reason I'm keen on flutter is that it would explain a halving of fuel flow during the time its cycle was "closed", against the LP port.

Re-Heat: A little too cryptic for me, sorry

rgds Airfoil

Point taken.
However, being jumped on by the bean counters because it broke at 152% is not ideal, either....
Should probably be discussed somewhere else, because it's an interesting notion.

Or it could be that when the fuel flow rate increased with the power increase, something got sucked into the pickup screens (that later disappeared) thus reducing the flow and was held there by the suction until impact. In theory this could fit the facts as we know them.

How many fuel pickups are there per tank, 3?

Precisely. And some form of that
 

posit feels nearest the fact given the Data. Restriction in the form of ice crystals was mentioned by D. Carbaugh, Boeing Chief of Safety Pilot. The restriction of the Fuel itself, as a too viscous mass or a too energetic mass, full of pressure waves and other considerations, all are important to explain the low fuel supply at HP.

Machaca, thanks for the visuals, great help.

Airfoil

Yes, thanks Machaca.

It looks likes there are 3 fuel pickups for each tank (left and right). Each of the 2 boost pumps (per tank) has it's own pickup, and the suction feed has it's own pickup. So nice redundancy for fuel pickups, but this means 6 fuel pickup screens would have to be blocked, all at nearly the same time for this scenario to be the culprit.

Which
 

makes a more reasonable solution one that isolates one or two crooks or crinks, but those needing to be vulnerable to the cause of fault. And vulnerable in the sense of simultaneous failure (~8 secs.). I look suspiciously at FCOC, and the plumbing around it. What a swell place for ice crystals to cascade into a clump and choke the life out of our A/C. Or like a cocktail shaker to block flow due to agitation and foaming. Boeing has the answer in the test cell(s).

Airfoil

The problem with the FCOC is heat is transferred from the oil to the fuel. This would seem to reduce our chances for ice formation between the LP pump and HP pump. Further, we haven't heard anything about any possible ice damage to the HP pump, only suction cavitation damage.

I don't know, maybe the fuel was as thick as mallases.

What's interesting is that both engines rolled back to virtually the same power level, EPR 1.03 and EPR 1.02. So not only did the restriction or obstruction occur at virtually the same time on both sides of the airplane, but the amount (quality, quantity) of the restriction was virtually the same on both sides. I'll bet the suction cavitation damage is virtually the same on both HP pumps as well. I wonder if maybe Re-Heat is on to something here.

Restriction
 

had to have been a transient, and fuel related. Scrapers, plastic, condoms, not possible, the block was a phantom, then a plug, then a phantom. What type of material would flow just fine at green descent, flow more slowly as flow and pressure increased, then mimic a solid, resisting all power and pumps to get it to move along. A change in phase? likely. A change in viscosity? easily. How about a change in energy content. John Green? (not caloric, but entropy)

Flight safety, I'm glad you brought up Oil Cooling. A thin oil, jet lube does not do well in very low temps. Fortunately it can be cooled by fuel, but wait, we need to heat it. Congealed oil in the cooler? Subject to convective cooling by the airstream at -70? Why should frozen oil bother 038? There's plenty left in the case. But if some is locked up in the FCOC and further cooling the fuel, well that's a horse of a different hue. Temps in the cooler? energy at 1.57EPR in the cooler. Where is the bypass? Does it matter? Who needs ice when the temp in the FCOC is -70C? Thaw? sure, give us twenty minutes. Pure speculation.

Whatever the restriction or obstruction was, it was very consistent on both sides of the airplane. This should be an important clue because with this kind of consistency (on both sides of the airplane), this should a reproducable failure (since it already occurred twice the same way, on both sides of the same airplane).

I have another idea.

I noticed looking at the drawings supplied by Machaca, that all 3 fuel pickups are located next to what appears to be a bulkhead between the main tank and the center wing tank. Since the center wing tank was basically empty at this point in the flight, what would the temperature of this tank have been? If this empty tank was colder than the fuel in the main tank, how would this have effected the portion of fuel in the main tank located right next to the bulkhead (where the fuel pickups are)?

I think for there to have been a double failure so close in time, it's necessary to look for areas where parameters would be fairly close in range. The Spar valves shut at the same time could initiate cavitation but would make both environments (fuel lines) dependent on the "same" "set" of conditions. The volume of the lines, though similar, would have been susceptible to varying results from suction due to connections, tubing strength, indeed even the "position" of the valves themselves.

When I think of cavitation, I visualize a smallish tightly sealed space subject to great energy at one end and collapse close by (shear). I'm looking for a block close by the HP's, one that reacted to parameters present in spite of all engineered precautions and anticipated challenges.

On the other hand, the delay of 7 seconds could represent the "differences" in systems' reactions to the fault: partial "collapse" of the piping to fixed values, time for two spar valves to close completely having lagged, run up of the lobes of the HP's to max, all other junctions to reach maximum deflection due to demand, etc.

Question: Could cavitation itself have been responsible for loss of commanded power and failure to respool? Only in the sense that it represents the "onset" of fault, the plug would have been responsible for the transition from "cavitation as evidence" to starvation and ongoing low power. 1.02 and 1.03 EPR mean not much is happening in the thrust department.

FS: I think the empty center tank would have performed more as an insulator than a chiller. Think Thermos.

Double failure . . .
 

Posted by airfoilmod:

There may have been a time lag between the two spar valves closing, either at initiation or in travel time. One valve may have been slightly faster than the other. Depending on what hypothetically would have caused such an anomaly, one valve may have closed further than the other before restoring to normal condition.

Not necessarily so. Remember the engines were initially accelerating, demanding a considerable increase in fuel flow. Sudden deprivation of demanded fuel feed, depending on timing and rate of the reduction reaching the HP pumps could lead to the same results.

Fuel lines (LH and RH) between the spar valves and the engines are similar and almost a mirror image of each other. From the spar valve the fuel line initially runs parallel to the rear spar and then makes a 90 deg. turn forward following a rib then bends slightly inboard before making another turn outboard then forward and inboard again (going around the drybay) before finally going relatively straight forward, entering the engine pylon and finally going downward connecting to the engine fuel line. Viewed from the top the fuel line path roughly represents a Z shape followed by a U shape (around the dry bay) and then straightening out into the pylon area.

However, (depending on many "ifs" yet to be answered) if the spar valves were affected in the way i described at the very beginning of this thread, it should not be ruled out that the APU fuel shutoff valve (and perhaps the APU remote shutdown) electrical circuitry was also affected. If the valve was electrically opened in the same action the spar valves were closing, all of the fuel lines between (partially closed) spar valves (closed Xfeed valves) and boost pumps in the fuel feed manifold of the LH fuel system could have been acting as an accumulator providing just that much more buffer in feeding the LH engine before rolling back 7 seconds later than the RH engine did? The APU fuel supply line is a very long line going to the tail before ending at the APU fuel control unit. With a system out of wack, that APU fuel control would probably have continued to shut off fuel supply to the APU. Just as a reminder, there is still no official answer as to why the APU door was in the open or partially open position at "touch down", of which there is photographic evidence.

An empty center tank filled with air and fumes will adjust faster to ambient temperature than a main wingtank (partially) filled with cold soaked fuel. Furthermore, the center tank temperature is also affected by the heat radiated from the airconditioning systems directly below the center tank.


Green-dot

USA FAA Contact URL re BA038 777 Accident
 

Given the continuing interest in this accident, the following URLs are links to the US FAA reporting site. Interested parties can access the site and drill down on the current status. The names and positions of US investigators are identified on the first site.

We continue to await governmental, industry and knowledgable individual insight into this potentially catastrophic incident. When you get to the page, click on "factual" PDF page for most complete information.


DCA08RA028

http://www.ntsb.gov/ntsb/GenPDF.asp?...08RA028&rpt=fa

precept

Where:confused:

The NTSB site layout is not too intuitive and it's search function is spotty.

Here (link) is a place that you can find all NTSB work-product on foreign investigations, just look for G-YMMM. However, there is really nothing new in there.

NTSB - Aviation - Foreign Investigations

If you suspect there is something in the official docket, but not shown on the website, then you can make a request for that record here:

http://www.ntsb.gov/pubmail/pubmail.asp

Sorry to ask the question...did anybody (bar the BBC) ever see or find a url to the BA internal report? thx

Hot rumour at LHR this morning that there has been another 777 engine roll-back.

More than a rumour. One engine failed to respond to throttle demands in cloud. Other engine OK. Both OK when leaving cloud.
Sorry don't ask, thats all I know.

Happened last Sunday a/c MMC. Whilst at F/L 370 engine did not respond for 90 seconds. Aircraft is still at LHR, AAIB have inspected it.
D

Can bigots pin this on contaminated Chinese fuel again? If so many will be clamouring for the boycot of the PEK Olympics........danger!!!!

DILLIGAFF,

Thanks for the details.

Here is an interesting article which may be related to this latest incident:

High Altitude Engine Flame-Outs | AVIATION WEEK

PS. Apparently asking a few simple questions about altitude and flight phase, just prior to your post, was reason enough for the mods to remove my post? :=

Regards,
Green-dot

MMC incident was caused by ice crystals forming on TAT probe as A/C flew through cloud leading to a false reading. When A/C came out of cloud ice melted and fueling returned to normal engine throttled up as requested.
By the way the F/O was John Coward.
D

High Ice ( in thin cloud ? )
 

Lucky Coward,
Arent those pitots heated ?

......Was that stuff about high engine ice in strange forms by Prof/Doctor Viellette, (Aviation Week last year) promulgated to all working Aircrew?
.......It seems essential information to me, and should have been shown up in this BA 777 thread at the very beginning by one of you current Captains.

.......I had a reliable report last month of CB up to 80,000 ft in USA . ......... I have seen thin anvil stuff 100 miles ahead of an actual CB-and got iced up pitots at 40,000
(pitot heat working, 3 aircraft lost ASI)

BA38s engines "Hesitated"
 

Dear Green-dot,

Thanks for the article: "High Altitude Engine Flame-outs" that tells us, we have been flying around not knowing the hard facts about engine icing. And that we still do, since advanced testing is still taking place, also in 2009.

Green-dot please reread our exchanges from may 1. and 2. 2008 in this tread, "your" article just sharpened my theory:

"That engine core icing was the reason for the BA38s engines hesitation"

Oluf

While I appreciate the latest news about possible engine icing at altitude, I do not believe that it has been linked in any fashion to the BA038 event durring an approach phase at non-icing conditions.

If the speculators and theorists among us want to discuss this aspect then I think that it needs its own thread or else a positive link via the AAIB

BA38s engines "Hesitated"
 

Dear lomapaeso,

It was indeed: "Icing condition" during the last 10 minutes of BA38s career.

Ground temperature was +11 degrees C. and its RR engines flew in and out of broken clouds.

Boeings definition of "Icing condition":

Anytime the OAT (temperature) is below +10 degrees C. in moist air (dew point within 3 degrees C.)

And the higher the temperature, the more severe is the icing condition, due to the higher cloud water contend.

Read more about it here: www.whistleblowers.dk

Oluf Husted

Service experience generally indicates that turbine engines are not susceptible to mixed phase or glaciated icing conditions, with the possible exception of two known potentially vulnerable engine design features. These two design features are (1) pronounced inlet bends (such as particle-separator inlets), or inlet flow reversals, where inlet flow can stagnate and accumulate ice, and (2) high solidity dual row front stage compressor stators that can be susceptible to non-aerodynamic ice buildup on the stator airfoils resulting in core airflow blockage. These two design features should either be avoided or carefully scrutinized by analysis and testing to assure their non-susceptibility to mixed phase or glaciated icing conditions.

I know it is a bit off topic but which jet engines fall into thise two categories?

In category 1) I would think you'll find engines such as helicopter turbines, some turbo-props, and some ancient engines with centrifugal compressors.
Not sure about category 2)

The poster's highly emotional comment, and the underlying concept, are misplaced here.

A number of reasonable persons consider fuel a likely or at least possible cause for the power failure because it is one of the few critical elements in common for both turbines on BA038.

Quite early in the post-incident investigation, the investigating authorities clarified that the fuel was not obviously 'contaminated' . Some people see as possible, however, the concept that the fuel might have met all prevailing specifications and still might have had some property differing from other "normal" supplies in common use, thereby defining an uncommon circumstance that might help explain why 038 uniquely had a problem.

The aviation community is international and very cosmopolitan. In regard to matters of safety, the focus is on finding answers and preventing future failures. While individuals may have their own biases, the consensus interest is directed toward empowering safe and reliable global aviation for all parties and all nations - not looking for persons or places to blame.

This is clearly not fertile ground for bigots, so please try to get a grip on yourself.

arcniz already has mostly answered this...

bigots? Haven't really seen any here. Some far-fetched suggestions, yes, but that's what R&N is all about.

contaminated ... fuel? It already seems to have been established the stuff wasn't contaminated.

... Chinese fuel? Maybe the particular 'cut' of fuel may end up having some relevance, although it sounds less and less likely. Tons more of the stuff were uplifted on the same day from the same place, and nobody else ended up just short of the runway.

... again.? The venom is in the tail. When did this happen before?
In short, I think we can class this one as a wooden-spoon-stirring post.

Far more interested in the ice accretion discussion.
As a non-engine engineer, I thought compression heated the air.
So with an OAT of about +10°C, wouldn't any earlier ice have melted rather promptly, once OAT was over 0°C?

Dear Oluf,

Having re-read our May 1st and 2nd exchanges i can see (as i did then) your point regarding core icing. Although i keep several options open to the cause of the BA038 accident, the AAIB reports so far reveal no indications that engine icing is suspected. The AAIB specifically stated in the S3/2008 bulletin, released in May (after our exchange), that there was no evidence of core engine icing and that the reduction in thrust on both engines was the result of reduced fuel flow and all engine parameters after the thrust reduction were consistent with this.

To my knowledge, if an engine rollback was caused by core icing, EGT would have increased (with fuel flow required available). Quoting the article on "High Altitude Engine Flame-Outs":

"Incident investigators using data from DFDRs found that the uncommanded thrust reductions were manifested initially by a gradual decay in fan rotation speed and a final stabilization of the engine at a sub-idle operating condition. The engine speed decay was also associated with an increase of turbine gas temperature and a failure of the engine to respond to movement of the throttles/thrust levers. The term "rollback" has commonly been used to describe this condition."

The recorded engine parameters, according to the AAIB, do not show high EGT readings consistent with possible core icing. However, not ruling anything out before the cause has been substantiated by facts, could BA038 have flown anywhere near thunderstorm anvils along its route that day, possibly accumulating ice consistent with what has been described in the mentioned article? I assume the AAIB will have looked into that possibility?

I do not rule out your theory. Although the rollbacks occurred at low altitude, ice accretion could have commenced at high altitude near TOD, keeping compressor temperatures low enough during the CDA for more ice to accumulate at lower altitudes. If so, the recorded engine parameters revealing the contrary, will have to be explained.


Green-dot

Technically speaking, ice (water) doesn't thaw until +4 Deg Celsius. But I know that you knew that! Pedant mode off.