At first siNeed to correct you. The DIFFERENCE between LH and RH installation was only 1 sec.
Roll back occurred after 7 or 8 secs.
Sorry if 7/89 looked like a fraction.

Hate to correct a correction, but according to the AAIB the difference was around 7 seconds, not only 1 sec:in addition to any asymmetry in the fuel feed geometry (possibility mentioned recently), there are other asymmetries which might possibly be relevant when looking at this difference.

eg. Fuel levels were not identical in each wing (300kg difference I recall), and also one wing would have been in sun and the other in shade, therefore likely to be some temparature difference.

Happy to note
 

That another poster has noticed the sunny side was to Port.

Airfoil

(especially in conjunction with #1, #2 "jet lag" as it were)

A little more on resonance
 

ChristiaanJ
As the troublemaker who suggested resonance a few pages back I would have to agree with you that ‘As an explanation ...it seems somewhat far fetched’. However it seems whatever is finally determined as the cause of this fascinating problem is going to be something quite out of the ordinary given that this is still apparently eluding every attempt at exposure by the amassed genius of the AAIB, Boeing and PPrune correspondents to mention but a few!

Your further statement ‘…any “fuel hammer” effect is nearly instantaneous…’ is however absolutely untrue and very misleading.

Lomapaseo

In order for resonance to occur within the fuel system, I suggest that there is not one simple explanation that will satisfy the enquiry ‘But what is the forcing function and the response’ beyond the observation that there are pumps providing energy to a flexible structure (pipework and fuel) that includes non return valves which in certain very unusual and very undesired circumstances have the potential to block the flow of fuel as well as to more normally allow it to pass.
It is the (very unusual) specific combination of many different factors within the above, each itself within normal parameters that could lead to the system malfunctioning as described in my earlier post.

Barit1

If this resonance did occur and was enough to restrict the fuel flow, the frequency has to be in a range that will include the possibility of the non return valves being able to oscillate between a closed and probably fully open position. I would reckon this to be somewhat less than 10Hz but in any case far less than the likely frequency of the gear teeth meshing of the HP pump.
A far more likely source of would be the airframe vibration that is typically experienced in a final approach with plenty of flap and low airspeed. Even so, it is only the effect of this combined with the specific combination of other factors that – perhaps – could result in the fuel system going into this rather inconvenient state of malfunction.

Flight Safety

If a system such as this did go into a state of resonance, while the fuel demand remained low, adequate flow was apparently anyway maintained. Increasing the fuel demand in this circumstance however would exacerbate the difference in pressure on either side of the non return valves causing either or both the amplitude and frequency of oscillations to increase but the fuel flow to decrease as an ever increasing amount of the energy supplied by the pumps is absorbed in accelerating and de-accelerating the column of fuel within the pipes, generating shock waves and in accordance with Newton’s 3rd law, powering the reactive movements of the mass of fuel line, components and other connected structures.
As this situation developed, it is also of course very possible that the rapid changes of pressure and depression may have begun to release trapped vapours from the fuel which then begin to foam causing a further sequence of effects that have been discussed in previous posts.
The known end result is that whatever the reason, very little of the oily stuff got to the burners of the engine.



Regards to all!

JG

To Joetom,

A spar valve in a position between open and closed most likely would have resulted in a (LH/RH) spar valve (actuator) disagree EICAS message when the actuator is not in the commanded position. A not fully open engine fuel shutoff valve would have been detected by the EEC.

Even in the very unlikely case faults would not have been detected, the most likely moment either of these valves would have malfunctioned is during engine start, the only time they are operated until they are closed at moment of engine shutdown. Both LH and RH side failing at the same time although not impossible, it is very remote.

During a normal engine (auto) start, the spar valves are opened manually by the fuel control switches and engine fuel shutoff valves are controlled by the EECs. Although the fuel control switches are manually selected from cutoff to run position, the timing of engine fuel valve opening is controlled by the EEC, it keeps the valve closed until the engine reaches the appropriate speed.

If the valves were only partially open, and if (in the unlikely event) faults were not detected by the EECs during engine start, the problems would have certainly surfaced during the takeoff roll when fuel flow is increased to meet takeoff thrust demand, a much higher demand than the thrust adjustments during final approach. A scenario for both spar valves to move away from commanded (open) position during cruise or approach has been discussed several times in this thread. Lack of evidence as to how this could have occurred prevents that discussion from continuing at this time.

Green-dot

Just to put some figures, we said earlier that fuel flow for flight idle should be around half liter/second and probably not far from 10x that amount for takeoff thrust ... (/engine)

Point taken.

Although... I remember the F-14A prototype went down due to a similar (hydraulic system) failure on its second flight, not after x million flights/landings.

I'm still baffled by the number of holes in the cheese having to line up for this to happen for the first time.

Point taken.

The farther back we take the the history of the aircraft, the easier it is to find a unique set of circumstances. So looking at the centre tank (a common feature linked to the two independent wing systems) it had a sub-zero cruise out followed by a sub-zero descent. These are the flight phases when atmospheric water enters the tank. Water scavenge does not work well below freezing, and I understand water warnings are occasionally reported when taxiing out after above-zero temperature fuel is loaded.

In this case the temperature at start-up for the return flight was below zero. If the fuel loaded was also below zero, there would be no water scavenge on take-off or climb out. The next opportunity for water to be scavenged from the centre tank would be aftert the descent to warmer levels, at which time it would be scavenged to the still cold wing tanks. Getting the holes to line up is not a problem - in fact it is a bit too easy, suggesting the holes are not big enough to bring an aircraft down.

For my money, the big question is how unusual is the history not just of that one flight, but of the history including the one before it and the conditions on the ground between the flights.

The cavitation damage statistics will be interesting. Any cavitation damage needs to be explained, because it is evidence of a fuel flow restriction at some stage of some flight. The fact that such damage is not unique to this aircraft might suggest that in this case there was just one hole too many, or the holes stayed lined up for just a few minutes too long.

The full explanation of the incident may well involve a long chain of coincidences involving more than one flight, and the investigation may take longer than usual as the correspondingly large number of alternative explanations are eliminated.

But there was no evidence of excess water in the fuel samples recovered ....

One value of different speculations about how an accident could have happened, is that it heightens awareness of how different accidents could happen.

To Green Dot,

My last post only mentioned Spar Valves as an example of how a problem can exist and fuel flow through the FMU/FMV can appear normal until it causes a flow short fall. I would not expect Spar Valves to be the problem in this case, but they have caused low flow during engine operations, and yes I know EICAS/ECAM will give this info to the crew all things being normal.

My last post was just to point out that a problem/failure mode could have been lurking about long before the 38 reached Heathrow.

I'm still holding out for 1 or 2 reasons for the events on that day.

Reason 1. Leak on a fuel manifold.

Reason 2. CWT scavenged fluid into wings that had very cold fluid in them.

Both the above could start a chain of events that may fit.

The interesting points I remember are.
1. Aircraft had a cold flight to PEK.
2. Aircraft had a cold 3 hour transit in PEK.
3. Aircraft topped up wings with fuel in PEK.
4. Aircraft uplifted neat PEK fuel into CWT.
5. Aircraft had a cold flight to LHR.
6. Aircraft had little or no holding into LHR.
7. Aircraft engines wanted more flow, but was unable to provide.

Be kind to me, I'm tired !!!

Resonance
 

I'm not sure I see how resonance could be set up (or sustained) in this system.

First, the fuel was cold and viscous to some degree. The non return valve is one way, thus tending to cancel any resonance (which is oscillatory in nature). Resonance requires a sustained oscillation with feedback loop, and in a system that normally would not excite resonance, if one were to form under certain specific conditions, it should be easy to break up the resonance with some applied external force. Just to remind you, there were operating boost pumps and operating HP pumps here, with one at one end of the fuel "column" and one at the other end. I would think the forces of the pumps should tend to break up any resonances that might form.

I think this applies so long as a major structure(s) does not provide the feedback mechanism, which would be harder to overcome by external forces. If major structure(s) contributed to the feedback loop, then the system would display natural resonance quite readily.

I also seem to recall discussion that the non return valve is in the suction feed flow path and not in the boost pump flow path.

Water hammer (or fuel hammer) is just a pressure spike created when a valve opens or closes (due to column momentum) and is not really relavent here I would think. Water hammer (or fuel hammer) does not normally restrict flow, but is rather a design consideration pertaining to maximum pressures seen by the system.

I stand to be corrected of course.

"The Non Return Valve Is One Way"
 

Not so. The function of the valve is to prevent "backflow" of the Fuel once it has passed the valve on its way to the Engine. The Valve sleeve moves in two directions, with flow (and against a spring), and versus flow, with the aid of the spring and the "backflow" of the Fuel, when it closes and prevents Fuel return. The mechanical "stop" can stall in any position, while transiting in either direction, vibrate (resonate) and completely stop Fuel entry into the system. All that is required (unlikely) is sufficient tuned energy to overcome the normal working parameters of the device.

I think some folks are visualizing the dynamic A/C system on short final without considering (perhaps) the level of energy and activity involved in landing 200 tons of incredibly powerful A/C full of PE and engines capable of lifting same. I remember my first experience watching the debut of PanAms first 747 in Honolulu. Relaxing on the beach at Sandy, about two miles from departure end, the A/C lumbered into the air "slowly". What dazzled everyone present was the sound. Everything shook from that spooky rumbling earthquake noise from the fans. the sand was vibrating on the beach.

Each of the RR engines has a fan that is probably too big to fit in one's garage, a device that can move air at a prodigious rate. Imagine each fan straining for purchase at full go, each Blade passing within a foot of the circular Fuel line around the shroud, inches from the Heat exchanger, and trying to disintegrate the HP pump. Feedback? The cold viscous Fuel in the Manifold has to resist carrying that energy throughout the system and still maintain flow within safe parameters. Resonance is definitely possible, and could easily occur given the right links in the chain. IMO.

In opposition people merely say, "Well, it never happened before."

Airfoil

"Ram". Resonance doesn't involve alot of "oscillation" My picture of Resonating fluid is a stalled stand (head), vibrating, rather asymmetrically relative to the "container". John Green might help us here.

Quoting Joetom,

With regards to reason 1:
A leak in the fuel manifold does not explain 2 engines rolling back within 8 seconds from eachother with crossfeed valves closed and an empty center tank.

With regards to reason 2:
According to the AAIB in their bulletin S1/2008 the aircraft's fuel tanks were last checked for water in the fuel on january 15 at Heathrow; this was prior to its refuelling for the sector to Beijing. Minimum temperature at Heathrow on January 15 was 6 deg. C, maximum temp. was 10 deg. C (I have temp. records for that day).

Warm enough to drain any water collected in the tanks if transit time was long enough between the previous flight and departure to Beijing. Since fuel samples taken after the accident revealed no excessive water content, it votes for correct water sampling on January 15th and that there was no significant amount of water in the tanks when departing for PEK.

So the flight to PEK may have been cold but if the tanks were "clean" with regards to water content when departing from Heathrow, steps 2 thru 7 become less relevant.

Regards,
Green-dot

Airfoilmod: Got a picture (cross section) of these specific one way valves?

Is it correct that at BOTH ends of the travel of the "restricting device" that fuel is completely shut off?

I'm more familiar with valves (spherical ball on a conical seat etc) whereby only one end of the travel actual restricts the flow.The design specifically ensures that flow is unrestricted in the other direction.

Interesting (if correct).

Two INDEPENDENT valves responding at the same time to some form of resonance (both systems likely tuned differently)...Possible but WOW!
Worse odds than the lottery!

Fuel properties
 

I have been following this thread from day 1. One might think that my daily involvement in the aviation safety business would mean that I would rather do other things after work than read pprune forums. Sadly perhaps -- in terms of my lack of more productive things to do on many an evening -- I find these sorts of discussions interesting and energising, sometimes even motivating me to wander off into some obscure corner of the web for hours at a time researching topics that arise from these pages.

So, here’s my comment: Over the past few years I've been directly involved in the investigation of aviation accidents and incidents, both civil and military, in diverse parts of this globe. 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

grizzled
 

I'll look for my very old post re: Icing Inhibitors in the uplifted Fuel in Beijing. I remember suggesting Propylene Glycol, Ethanol, and Alkylates. There are some Fuel guys here and chemists too, they'll most likely be interested in your post

Airfoil


#126,#144

FSII, if present in the fuel, might be a factor. I dicussed it previously in #1292...

However, I seem to recall that in an answer to my post, someone pointed out that the fuel filters would be automatically bypassed in the event of flow restriction?

Am I right in thinking that this is a new bulletin from the AAIB

http://www.aaib.dft.gov.uk/cms_resou...MM%2006-08.pdf

As an electrochemist I have spent much of my life trying to understand technical mysteries associated with various liquids and their specifications. Based on this, when I read in the latest AAIB bulletin that the fuel "in many respects exceeding the appropriate specification" I start to ask the following type of question:

Are there some components in the fuel which have secondary benefits which have not, so far, been fully realised? E.g. lubrication. If this might be the case, then concentrating on those possible benefits might be the key to the mystery.

Update
 

I think the release updates info to include the recon of the Fuel system and to announce that Boeing are now looking for "abnormal combination of parameters." (Having found no one "hole")

It's important to reconsider that "exceeding spec." does not qualify a Fuel as "superior" in quality. It is an easy mistake to make, but "exceed" means "beyond" as well and includes a description including "poor", "misses the mark", and suggests that whatever is present in the fuel may be degrading its quality and performance.

An FP of -57C can be acquired merely by adding light molecules. Acetone freezes lower than kero, as do any number of easily added off spec matls.

Resonance expalined - in part!
 

From the information supplied from this forum and some additional research, I understand the relevant components of the 777 fuel system to be; two AC powered centrifugal booster pumps mounted adjacent on the rear of each wing tank which feed into a common manifold. On the inboard side this manifold extends to become the cross feed (which has two normally closed parallel valves mounted only on the left side of the aircraft) and outboard becomes the fuel delivery pipework which passes through the spar valve, continues to the oil heat exchanger in the fan case and then on to the engine driven HP pump which is fitted with a recirculating bypass to control over pressure.
http://www.eatonaerospaceltd.com/fuel/Resources/021_2_Type9106boostpump777.pdfgives some details of the type of booster pump fitted.
I assume (dangerous?) that this unit is very similar to those fitted to some 747s of which I have better information. In order for it to be possible to service the pump without draining the adjacent fuel tank, a sprung loaded flap valve is located at the inlet of the pump case which is mechanically held fully open by the physical presence of the pump. On the outlet side, a similar flap valve – ie a disc with a hinge on one side perpendicular to the flow – is mounted. This is a typical non return valve which has a soft seat and a weak spring to ensure the valve will close when there is no forward flow and as far as I am aware no means of damping the movement.

Considering just the section of this system between the boosters and HP pump, any physical movement which even slightly changes the shape or concentricity of any part of the pipework also changes the internal volume of the pipe and hence introduces a degree of elasticity.
In the unwanted resonant state, a small surge of fuel progresses towards the engine where it is baulked by the HP pump which by its intended design strictly meters the possible flow. The excess energy contained in this moving column of fuel causes an increase in the local pressure creating a shock wave causing some slight expansion or lateral movement in the pipework which upon contraction returns a reflected shock wave back towards the booster pumps.
The non return valves are held open in proportion to the flow of fuel hence at engine idle the valves will be floating close to their seats. The shock wave hitting the back side of the valves momentarily forces them against the fuel flow direction and towards their seats. This causes a restriction to the flow creating a disparity of a depression on the engine side of the valve and an increase in pressure on the booster side. Once the shock wave has passed, this combined depression and pressure causes the valves to move rapidly to a more open position… causing a surge of fuel to progress towards the engine….

If the many and complex physical characteristics that are an influence allow the continuation of this feed back pattern, this system will continue to oscillate – ie resonate - until something either breaks the loop or as can also happen, exacerbate it although due to the enormous interdependent complexities involved, predetermining what will cause what response may be impossible.
It can be seen that on an increase in demand the HP pump allowing more fuel to pass might reduce the effect of the pressure build up and reflected shockwave and hence damp the effect. Alternately, the greater demand could result in the difference of depression and pressure across the valves causing them to open faster, resulting in an enlarged surge and a growth in the effect.
In the low demand situation with just a small amount of oscillation in the fuel column, the supply seen beyond the HP pump could remain quite adequate to cause no problem or alarm. If however on the increase of demand the oscillation is exacerbated, the supply will become increasingly restricted with all the energy being introduced to the system being absorbed in accelerating and de-accelerating the column of fuel within the pipes, generating shock waves and in accordance with Newton’s 3rd law, powering reactive movements of the mass of fuel line, components and other connected structures.
In this latter circumstance, a point will be reached where the suction of the HP pump causes such a severe pressure differential across the valves that the system will reach a limit where the flaps are moving with such speed and force that they will be bouncing between whatever mechanically limits the maximum open position and the fully closed positions. In this state the liquid managing to get past the valve will be a fraction of the normal full flow and at which time it becomes anyone’s guess as to the state of the fuel – or foam - between the HP pump and valve.

I have omitted a rather critical part of this explanation until now which is ‘So what caused the resonance to start in the first place? The simple answer is that in this particular case I really don’t know! However, if you can understand the explanation and visualise a horizontal column of pressurised liquid passing through a slightly open flap valve and then giving that pipe a little sideways shake perhaps you can see how easily it might start even though there are so many other parameters that have to be ‘just right’ for it to have any chance of self perpetuation.

If this overall scenario as described seems unlikely to begin with, it is made even more so by the fact that there are the two parallel non return valves on the booster pumps and for the effect to develop it is actually essential for them to react simultaneously. In the first instance this may seem absurd but they are both identical, operating close together in an almost identical environment and being induced by the same forces. Even if one valve does slightly lead the other, once even slight pressure variations begin, it is quite feasible that they would operate in perfect unison.

Rather than rewrite the details, I explained in my original post #1165 how once started, this effect could propagate from the right to the left side taking a few seconds to do so.

Still so very many holes all to have to line up…



Regards

JG

sky9 - That's no new update
 

The update you refer to is a previous release, 3/2008, issued in early May.

The 16 June date on the website relates to the 6/2008 AAIB Bulletin within which is published (again) S3/2008.

I might be wrong but I can't find any changes in the two documents except someone has edited the earlier document to name it S3/2008 when previously it was called 3/2008.

Might be wrong though.

Note to myself: I must get out more.

regards, Tanimbar

johngreen

No sense in talking about resonance unless you also include dampening (friction losses)

Forcing functions are common place, undamped resonance is not.

Lomapaseo

The circumstance described is most certainly unusual but I can assure you regardless of friction losses, there are occasions when very different systems in different conditions and with very different fluids will behave exactly as I describe.

regards

JG

So the discussion enters its
 

fork in the road. To damp the energy within the piping, absorbers,(damped mounts) must be tuned for all forseeable mechanical vibration. To that extent, a certain flexibility needs to be engineered into the mounting of the piping. But wait, if there is too much, the Pipe and Fuel can act in unison, which would conceivably block flow. So what is the design of the pipework relevant to the contained and flowing Fuel? And let's not forget forces other than resonance. Like Harmonics, Flutter, coef friction values dependent on fuel type and source. This is getting interesting.

Airfoil

At the point of entry of this discussion, system isolation and ETOPS are frankly irrelevant. Two systems on separate A/C could behave identically with one another given the ineluctable power of certain anomalies and reasonably similar parameters. Lose the seductive and nonrelevant impetus of ETOPS, or lose the basis of debate. This isn't about how incredible it is to entertain the thought of concurrent failure anymore, it is a given.

Is it a fair observation that more engines would not be the solution? If there were four engines would all four give inadequate power with the same outcome?

Not as easy to answer
 

as it may seem. If two heretofore simultaneous failure proof systems have just failed, and not due to all the engineered in safety of ETOPS, then the answer is no, twelve engines would have failed the same way. Isolation from bowser to chox is possible (At ridiculous cost), so by definition we're dealing with a non Etops issue.

My mentor and his co-pilot ate the same pork sandwiches on their way to bomb Tokyo in 1945. Both got food poisoning and were unable to fly. The chicken sandwich got ate by the navigator, who was an eager ab initio student on the way back. Separate everything for each side on the ETOPS twin? Ouch, you think Fuel's expensive.....

Airfoil

At a recent safety conference attended by a Boeing accident investigator, it was revealed in social discussions that Boeing had failed to find any mechanical, environmental ice, or other aircraft malfunctions as causal factors, however, have attributed the malfunction to interference with the fuel pump electronics from a laptop computer being operated against airline rules by a senior British government official over the top of the area of the pumps.

I doubt that theory, as no Senior British Gov't official would be sitting that far back in the cabin.

safety conference ...
 

HP fuel pumps are mechanical ... not sure there is any electronic involved (?)

Hmm....
Silly late night thought. If senior government officials could be persuaded to sit directly above the high pressure fuel pumps it might solve some of our other problems.

I'm 99% certain the reference to "interference with the fuel pump electronics" must really mean EMI to the FADEC. However that does not explain the fact that the fuel metering valves were commanded open, but fuel actually delivered was a fraction of the demand.

Sodden thought
 

Restriction between heatexchanger and FMV would explain both HP high side cavitation and no additional flow at valves; similar result if restriction was the H/E or prior. Not a "Pull" problem but a "Pack" problem.

I find it very gratifying to see so many informed and thoughtful people putting their heads together on the "outside the box" analysis underway. In the worst case, this discourse burns some time but stimulates flexible thinking about things that others might readily accept as "status quo". In the best case it may allow or inspire people in the official determination loop (and in the aircraft systems development stream) to work a bit harder at understanding the outer margins of probability for failure in the marvelous products they devise.

Comment on two recent posts:


I would suggest that your concept is very promising, but the conclusion is incorrectly stated:

The effect of the submerged boost pumps running will be to keep dissolved gas IN solution, because the pressure gradient across the pump is relatively gradual (with fluid present at both inlet and outlet) and the pressure added by the pump is not so large an increment to the gravity feed pressure of the surrounding fuel.

If, however, the boost pump ceases operating, then a larger pressure gradient develops at its outlet side due to the suction of the HP pump and engine. This increased suction pressure gradient would likely be the cause of dissolved and otherwise entrained gasses increasing in volume and coming out of solution in a way that might disrupt the overall flow.


-------

Johngreen's detailed explanation of resonance is very informative as a baseline for discussion.

My understanding is that the resonant couple in a plumbing system like the 777 fuel supply path includes at least the two normal tuned systems, plus possibly other parasitic resonances. A first tuned/resonant path is the plumbing, pipes, etc, and the terminations formed by pumps and gates and valves. A second is the fluid, gas, or whatever may be rattling around inside the plumbing. Outside structures and forces may contribute to additional resonant loops.

A teasing difference of circumstance in the BA038 context is the history of very cold fuel. Someone has credibly noted that JPxx fuel viscosity is characterised only at -20c (iirc) in the standard fuel spec, meaning the viscosity might differ widely with varying fuels in the regions above and below -20c. Clearly, fuel viscosity will affect flow characteristics as well as the propagation velocity for shock waves (which controls resonance behavior). Could it be that the very cold fuel temps changed viscosity of a somewhat non-common fuel in such a manner as to put the resonance propagation velocity characteristics of the fuel outside the range of modeled behavior used in the 777 design calculations, and therefore outside the damping ability designed into the system?

If low temps, uncommon fuel, and resonance possibility were factually linked to the chain of causality, one might have a very plausible failure mode.

I'm not sure I accept the resonance theory, but for the sake of discussion....

Years ago I once had a hot water shower faucet that resonated. It would start as the water got hot (temperature induced). The typical screw type faucet was many years old and the screw stem part was worn. When the resonance started, the rubber part of the valve (at the end of the stem) would oscillate from open to closed to open again on the valve seat. When the resonance occurred, the water flow would reduce (the valve being closed part of the time). I assume the hot water made the copper pipe flexible enough to allow the resonance to start. Naturally the resonance would occur at the moderate setting appropriate for a nice warm shower (if you held the handle with your hand the resonance would stop), which meant the valve had to be open or closed more to stop the terrible noise (resulting in a too hot or too cold shower), so the valve being open a certain amount contributed to the resonance. The fix was to replace the worn faucet with a new one (where the stem would not move and thus would not resonate).

Now to this accident.

There was no flow bypass in the shower example (which would have prevented or damped the resonance and provided alternate flow), and the energy feeding the resonance (since all resonances have losses) was the available water pressure. In the 777, we have 2 fuel pumps on each wing (boost and HP) capable of providing the energy to sustain a resonance. My question is in a 777 fuel system, do we have a valve in a common un-bypassed path between the tank and HP pump, that can restrict flow fuel if driven open and closed by a resonance?

Still
 

I think it important that other sources of energy be considered. Resonance is intriguing, and damping the pipes, etc. The energy provided by Boost and HP is substantial, but more than this, consider the introduction of massive vibratory and sonic input from core and fan. This is what happened, by report, (Initially responded....). A cold and viscous fuel in a slow, low energy green state is assaulted by enormous and rapid changes, locally, and we talk about tap water? A "length" of contained fuel may not react well to local insult of 35k kg of thrust and all the intricately timed reactions inherent in the system. Envision a long narrow mass (fuel), vibrating (in sequential expressions relative to its proximity to the energy source) and ponder what all the vibration is doing to its mass, and include sonics, flutter, (valves), etc. It is not for nothing Boeing has assembled the entire fuel system at test.

Airfoil

Interesting that modern, greater precision could result in more accidents (similar perhaps to the greater navigation precision we see today that heightens danger to aircraft flying on the same airways through the airway centreline rather than scattered through the airway).

The implication is such that ever greater precision is not desirable, and requires exponentially greater understanding and testing of the small defects that arise now the larger, obvious defects have largely been solved...

Resonance ...not
 

If the oil heat exchanger is located in the pipe network of only one side, then the separate systems are not mirror images of each other. Similar resonance to dis-similar systems at about the same time is highly unlikely.

Re-Heat
 

Your view is one that, I think, will be repeated and strengthened over the next few years. Although it may contribute to "thread drift" I must opine that you have identified what I believe will become the prime aviation safety issue of the next decade.

Re-Heat

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



Agree. but only when we have acheived a factor of ten reduction in accidents due to the more obvious causes (excluding BA038.)