Bunk-rest
 

If AAIB are that sinister, they certainly wouldn't need hints from the likes of PPRuNe. And if they're straight-up (obviously), conjecture doesn't hurt. What you seem to be suggesting isn't helpful, unless you're trying to be funny. Every venture undertaken by Human beings requires a little Faith.

Additives
 

Smilin Ed, in respect of your last (1261), I think not.

"Do I interpret this discussion correctly? Is it being said that whatever caused the freezing point of the fuel to be much lower than typical caused the fuel to not be properly combustible?"


I'm not a fuel chemist, just a pure chemist of sorts and hope to be corrected if wrong by those in this thread more knowledgeable than me, but simply shortening the average alkane chain length in the fuel will be the basis of the lowering of the freezing point/waxing point temperatures, not the addition of non combustible additives.

Technically such changes will alter the Heats of Combustion a little but never so as to render the fuel non combustible. That the fuel was within spec is key.

The arguments for and against the effects of water scavenging additives (which are usually ether like molecules derived from ethoxyethane and inherently themselves very combustible) and / or fuel having become stratified, have been rehearsed at length in earlier posts on this thread.

CW :)

Stay the course BA 038
 

The BA 038 accident facts published to date make it one of the most significant events in aviation history. Those who respect aviation must keep the investigation front and center. Whether grey beard or shave tail, all of us must stay the course and do what must be done to bring this event to a conclusion which benefits each of us who dare to expand aviation.

Not as simple as that, works for short length C1, C2, C3 molecules as they are all around the same MP (Gotta love Carbon Bonding), but as the chain gets longer the melting point increases quite markedly.

Some T7 operators sent out a bulletin stating that they had some EAI valve malfunctions lately and Boeing is working on it. In the mean time crews are requested to test the system in descent.

In view of my early posting (#75), i am just wondering if this is not some coincidence.

But the visor is set on fuel and i concurr with Bunk-Rest's post of the 30th.

GMDS, I'm not able to see your early post ... Would you tell us a little bit more on that bulletin ?

CONF iture

The bulletin does not say a lot more than what i posted.

Sorry for the ref to my post, it was on a early but different thread about BA38.
Here is what I wrote. (I have to put it in the right timely context though: It was only three days after the accident, well before the AAIB report this thread refers to.)

Ok GMDS, but this doesn't fit with AAIB Bulletin S3/2008 SPECIAL

GMDS
 

How would that explain balking at Manuals, indeed no apparent change after cancelling A/T? Are you saying EPR would override FF in MAN.?

CONF iture:

Absolutely, that's why I backed off with my suspicion (I mentioned that my theory was very early in the debate). In my re-contribution just above I also clearly stated " ... I wonder ... ", as apparently ice was not involved. However, i still wonder ..... but backing off a second time.

airfoilmold:

in a situation as i described, it would make no difference if with A/T or in manual. In both cases the command to the EEC would be the same -> "gimme more diff press" and in both the EEC would say "you already have max".

GDMS,

When referring to the "engine anti-ice system", most pilots would call this the cowl hot air, that stops ice building up in the inlet then coming off in big chunks and going through the engine. AFAIK the various probes are electrically heated (like the main pitots) and I suspect would be on all the time, thus unlikely to block unless the icing was incredibly severe. Standing by to be corrected...

GMDS, Don't go anywhere just yet. Backing off isn't necessary either. I'm a trifle gun-shy on this thread, but the worst that can happen is, well, never mind. I can see a Pressure Probe (electronic) but a PITOT? My 777 architecture is insufficient it would seem. My engineering is osmotic and unreliable, but relying on an aperture signal rather than a sensor seems way archaic. Do go on.

Airfoil

FADEC
 

As an old one, I still have to think about Full Authority....... I keep thinking it has to do with a Beatnik's sound system. My manual throttle inputs need to filter through an EM spectrum sensor to have any effect? My God I so prefer Pistons. Excommunicate me if you must, but I'm all ears. Again.

Airfoil

The Trent P2/T2 probe is electrically heated all the time the engine is running.
The Trent EAI only heats the nose cowl inlet lip and the air (HP 3) is cooled prior to entering the nose cowl, this air is then vented overboard.

Agree But the probe heat does fail from time to time,

I wonder if it is annuciated (recorded) when it does:confused:

And
 

We are still stuck with a philosophical foundation to the engineering. How do TWO separate, isolated and independently controlled systems exhibit virtually identical (Failure) behaviour simultaneously.

Airfoilmod,

We still have pitots on the 777, according to Boeing. Managed to get a "HEAT PITOT LEFT" the other day.

The engine PT2/TT2 probe heater systems will generate "ENG EEC MODE (L/R)" status messages on failure.

P.S. Have you been at the duty-free? ;)

I wonder what would be found on other operators a/c if they carried out a random inspection of in service pumps i.e signs of cavitation wear etc?

similiar to the ba a/c with similiar hours/cycles?


just a thought......

Please don't overlook the FACT that FUEL, ENVIRONMENT and PROCEDURES are common to both installations.

Why do you assume FAILURE?

It is quite possible that no FAULT (i.e. DEFECT) occurred in the homologated imstalation. Just that operating parameters (possibly even STANDARDS) were (are) inadequately specified.
I suspect that fuel QUALITY is a "Black Art" and to a large extent relies on standardised manufacturing process to control various aspects of quality.

Since the initial AAIB report I have been concerned regarding the low fuel freezing point on the sample taken from BA038. It sticks out like a sore thumb!
Maybe some of you guys can provide DATA on what the expected RANGE of this parameter is. If, as I suspect, the range is normally in the order of +/- 5 degC from whatever is the agreed "norm" is, then what made this fuel have such a spectacularly different freezing point?? OR is this very low freezing point understood, and simply a red herring?

The fuel may be "in spec" but something was unusual IMHO about the sample(s?) measured.

Whether this unusually low freezing point was due to something linked to the original fuel processing / additives or whether it was the result of some strange in flight stratification process remains IMHO an OPEN question.
Even if the low freezing point itself is not an issue maybe it highlights (indicates) a fuel with a greater propensity to cause cavitation or whatever.,

A reason exists for this near disaster! With all the data that exists I find it almost incredible to accept that a (potential) cause / sequence of events has not been identified.

OK it may take time to CONFIRM any such potential sequence of events but although we are struggling with inadequate data I'm convinced that this cannot be the case for the investigators.

However, the part of this that I don't understand is why no activity has occurred to put in place more rigorous procedures at least till the sequence of events is published. e.g. Tightening of fuel min temp or whatever.

So maybe the cause is understood and since the RISK of a repeat event is considered LOW there is no need to rush out a further report especially if this is POLITICALLY SENSITIVE in someway.

All will become clear in the fullness of time!

This has Min (-78F), Max (-42F) and Average (-53F) for 19 jet fuels in the USA in 2005...
http://pps.ms.northropgrumman.com/aviation.htm

Hi,
Thanks for that report.

I assume these were all tests on supposedly the SAME type of fuel (Jet A1 or whatever it might be called in the USA).

The report doesn't indicate the specification limits nor the expected range limits for most samples.
So were these 19 samples in spec?

Differences look considerable. So why such differences?
This supports my fuel quality is a "Black Art" proposition.

I wonder why vapour pressure, calorific value etc wasn't (aren't) checked?

If I was buying aviation fuel in vast quantities I would want to be sure that the stuff wasn't being "diluted" or in other words providing less bang (mpg in car speak) for my buck.

Interesting.

Cavitation again
 

Snanceki sir, I very much agree that the evidence so far points to it being a fuel related event.

Without going over old ground too much, suffice to say that if we have an abnormally low fpt, and this fuel seems to have had just such, the lower intermolecular bonding levels that allow this fpt will also make for a correspondingly increased propensity for the fuel to go gas phase in the HP pumps - ie to cause cavitation when the FADECs commanded an increase in fuel flow rate at circa 700 feet.

A proper statistical picture of evidence of cavitation damage in other 777s would be very useful and I bet Boeing/RR have looked at this, hard. It could be more of a problem than is realised with all specs/SOPs et al on 038 being met with the unforeseen until now problem built in.

I have deliberately omitted further comments on additives and stratification.

Much respect from me for the chaps on the flight deck that day

CW

Chris Weston

You appear to be in agreement with my position.

i.e. Looks like a "standards" / design parameter issue.

Snanceki
 

Good Morning, Sir- Very difficult to read for understanding on the Net. I like to hear and see while discussing, old pilot. Your purpose in quoting my rhetorical question isn't clear to me. I must say though that the rest of your post describes my conclusions quite well, such as they are. My Bottom Line in this has to do with ETOPS. This isn't a generic incident for me. I get from your concerns that you may share my view. Without being specific, I believe that mitigating alterations to procedures have been created. I know of a few and believe that there are sufficient changes to protect the domain of Twin flight. Some are mentioned on this Thread, as well as other places, some are proprietary. To repeat something I wrote in February, just because one isn't directly aware of solutions doesn't mean they don't exist and haven't been engaged. To think in a fearful way that because AAIB haven't released a report sufficient to please all the interested public and somehow there is an unknown danger afoot is silly.
I have perfect faith in flying and in ETOPS.

BRGDS Airfoil

agreement
 

Snanceki you are correct, that is my basic view too.

But as ever, the devil is in the detail and for that we must wait.

I have unequivocal respect for AAIB too.

CW

:mad::ugh::ugh::mad:

Someone above published a survey undertaken by Grumman. It confirmed what I (and some others) have been saying from the start - namely that the formulations of jet fuels vary hugely depending on crude source, production process (eg hydrotreated, severly hydrotreated etc) additives used etc etc etc. The above list does all meet spec by the way. But for commercial privilege, I could publish a list of a few thousand jet samples, several hundred or so of which are off spec for a variety of parameters (but the high proportion of off spec results is not surprising given that I investigate Jet contaminations for a living)

The reported freezepoint for the subject fuel falls within the limited sample range (19 samples?) in the Grumman list - it was ABSOLTUELY TYPICAL of the value you'd expect to see. If low freeze points were a problem, Defstan/ASTM specs would specify a range of acceptable freeze points not just a maximum. So please, do not continually harp on that at the FP was lower than it should be - it was not.

Few other pointers from preceding few posts:

Vapour pressure: This depends very much on fuel temperature. The lower the fuel temp, the lower the vapour pressure. If the fuel had an abnormally high vapour pressure the problem would have arisen during highest fuel flow rate and highest fuel temperatures - which would have been at takeoff. In any event, if the vapour pressure was too high, it would have been off spec on flashpoint (which it apparently wasn't)

Cal val: If cal val of the fuel was insufficient to provide sufficient thrust to arrest descent, how the heck could the a/c take off in the 1st place? In any event, Specific Energy forms part of the spec, and there is no indication that this parameter was off spec.

Additives: The allowed additive list for Jet A-1 is very restrictive, and additives used must be stated on QC's. If excess or unauthorised addives were used, it would have been picked up on GCMS.

Another point: Various people have talked about stratification. If the fuel had stratified, and the "good" components been consumed during the cruise leaving only "bad" stuff (technical terms :ok:)- this would have been plainly evident to the AAIB by simple comparison of the measured quality parameters of the remaining fuel with the reported quality parameters of the supplied fuel. There is no suggestion in the AAIB reports that fuel quality differed significantly than certified at loadport.

Edited to improve the English (originally typed upon return from the pub ;))

Hi Mariner9,
So you are a Jet fuel "expert". Excellent.

If your job is Jet fuel compliance then this suggests that fuel quality is important although I have no knowledge of what parameters in the fuel may be of greatest concern and why. Maybe you could enlighten us.
What is the most common cause of non compliance?
What causes this non compliance?
Why is this deemed a concern?
Incidentally what happens to fuel that doesn't meet spec?

I suggest that you missed my point.
I did not intend to convey that the fuel in the subject aircraft was substandard in some way (the AAIB appear to have eliminated this by stating that the fuel was "in spec") but merely pointed out that ACCEPTABLE "quality" appears to have a wide range.

I certainly didn't suggest that the fuel was "so bad" that it wouldn't burn, for the reason you pointed out (would have been determined during take off/climb) but since Cal value = heat from fuel = Thrust, a lower cal value will give you less "bang for your buck".

HOWEVER, this wide range of acceptable quality MAY.... in some yet to be determined way..... have been implicated in the chain of events that occurred to BA038.

SOMETHING caused this incident.

As I stated I suspect we are talking about STANDARDS / SPECIFICATION /PROCEDURE boundaries in some way, otherwise the cause would have been determined by now.

Good morning.
I quoted your rhetorical question since I believe the answer lies in something that is COMMON to the two separate, isolated and independently controlled systems.

ETOPS, from my extremely limited knowledge of the subject, appears to be working well, but we should not overlook that fact that certain aspects of the (duplicated) installation are COMMON.

It appears that we may not be looking at something having gone wrong, but rather a situation where the interface between
FUEL, ENVIRONMENT, DESIGN, STANDARDS and PROCEDURES has created an UNFORSEEN situation / scenario.

From reading the AAIB reports, it would seem every component they've tested so far does/has work(ed) according to design parameters. This includes the integrity of the fuel supply system from both tanks.

We have symptoms of fuel starvation to the power units, cavitation damage to the engine pumps, tanks pumps still running (no pressure warnings) and plenty of fuel in the tanks: logically, this points to some restriction between the tank pumps and engine pumps. So far, nothing has been found, so the restriction appears to have been temporary in nature. I presume a lot of time is being spent trying to figure out what this might have been, especially as it affected both L & R systems almost simultaneously.

We're down to contaminant (nothing significant found yet), odd fuel behaviour (ditto), physical change to fuel lines to reduce cross-sectional area (no evidence for this at the moment) and ??

I'm hoping something might come from a detailed environmental test of the fuel supply chain - no news yet...

Right On Snanecki
 

Quoting snanecki, "If, as I suspect, the range is normally in the order of +/- 5 degC from whatever is the agreed "norm" is, then what made this fuel have such a spectacularly different freezing point?? OR is this very low freezing point understood, and simply a red herring?"

Right on snanecki! I tried to say this earlier but couldn't bring up the words that you have. :ugh:

My job is not routine compliance testing (though it was a decade :{or so ago), we only get involved once problems are identified.


Perhaps not surprisingly, the most frequent problem by far in Jet fuel is failure of the simplest test available - visual appearance, where the spec is "Clear, bright, and visually free from solid matter and undissolved water at ambient temperature". Generally, this problem can be solved by simple filtration. In extreme cases, the fuel is downgraded to regular kero or blended into gasoil.

Another common problem is flashpoint, particularly if the fuel is transported at sea after a previous low flash cargo. Reduced flashpoints are very difficult to resolve, necessary blend ratios are impractically large. Typically, the most economical action can be to re-refine the material, but that will always pose production problems to a refinery that is probably already maximising Jet output - additional kero in the crude stream will reduce output of gasoil and gasoline.

An interesting one, and possibly of relevance to BA038, is particulate contamination. This is measured by filtering some fuel, and weighing the particulates collected. An associated test (which forms part of the military spec) is filtration time, which specifies the minimum time for 1 US gallon to be vacuum-filtered. We have had numerous problems where anti-icing additives have been incompletely mixed, which for reasons we dont fully understand, cause difficulties in filtration. Obviously, filtration difficulties would impact on the flow of fuel through aircraft filters, and I would imagine that the effect would worsen with decreasing temperture. However, I have no idea if the subject fuel contained any FSII - chances are it didn't. I also don't know if the AAIB have had particulate contamination/filtration time checked as strictly speaking, the limits only apply at the point of manufacture. It would seem unlikely that they haven't checked this basic point however.

The remaining common failure is the JFTOT (Jet fuel Thermal Oxidation tester"). This arises where the fuel storage or transportation includes incompatible metals such as copper. It can generally be treated by the addition of approved metal de-activator additives to the fuel.

I didn't, but concede that I didn't answer it properly!

Briefly dealing with the "bang for buck" point first, the answer I give below should hopefully answer the main query posed by you and others, which I interpret as "even though the fuel meets spec, could the wide range allow the presence of unsuitable components that wont burn properly"

Specific energy for Jet is specified at minimum 42.8 MJ/Kg. However, it does not have to be measured. Instead, it is acceptable to calculate the specific energy based on certain measured quality parameters (density, distillation recovery temperatures, aromatics content, and sulphur content). This shows that the authorities consider it reasonable and safe to conclude that a fuel which meets spec for those key parameters must produce sufficient energy, even if the material is not wholly "kerosene". Rest assured, this has been based on years of research and analysis. Clearly, they do not consider that other materials with similar parameters but adverse energy characteristics could be substituted. In any event, other burning characteristics of the fuel such as smoke point are checked.

However, I (and presumably the AAIB) accept that while this is a reasonable assumption, it would have to be checked out for the subject fuel. I would be amazed therefore if they have not yet measured the specific energy of the fuel. The point remains however, if the SE was low, the aircraft would never have got off the ground. Also, flamibility issues could not account for the apparent cavitation damage.

Certainly did, and its clear that the fuel has to be one of the major suspects. However, if it was, I would suspect it was more to do with its fluidity/pumpability in a combined low fuel temperature/lowish fuel quantities (minimising the net positive suction head available) environment than any other quality issues. (Cant recall whether I've mentioned this before, but the viscosity of Jet is specified only at -20C)

Fuel did not have "spectacularly different freezing point"
 

Some here are saying the -57C freezing point of the remaining fuel is spectacularly low.

Actually this does not seem to be true. If you examine what Shell have to say about fuels around the world, you will read that there are many different grades, different constituent standards and different methods of measuring temperatures.

http://www.shell.com/home/content/av..._10081004.html

There are Russian and Chinese sections on the above page. I mention Russia because there have been reports that the indigenous Chinese suppliers cannot produce enough fuel and have been importing Russian equivalents which have "a low freeze point (equivalent to about -57 degrees C by Western test methods)" - quote from the page above.

My view is that we here don't have enough information to make any conclusions about the provenance, name, constitution etc. etc. of the fuel on BA038. All we know is that the AAIB say the fuel, "complied with the Jet A-1 specification".

Regards, Tanimbar

They are, but rest assured, it isn't.

If it was TS1, it would not have met ASTM/Defstan Jet A-1 specs for flashpoint.

The entire fuel manifolding from boost pumps to the engine interface has been removed intact from the left wing and is at Farnborough. It is installed in a test rig for simulation purposes.

The filters have a bypass! The filter is monitored by the diff. pressure s/w which would send a discrete signal to the engine EEC before the bypass valve opened.
The result would be a status msg. ENG FUEL FILTER L (R)

Mariner
 

A friend @ Northrop/Grumman, a Thermal engineer has pointed out the discrepancy that follows. Freezing point of -78, -53, (Average)and -42 Maximum are expressed in degrees Fahrenheit. Quoted OAT (at times) along the noted Flightpath are -78 degrees with Fuel Low Temp of -38 degrees, Centigrade. Should the discussion revolve around values expressed in the same measuring system?

Gas Path, does the Fuel/Oil Heat exchanger also have a bypass, allowing for flow should the Heater Plug Up?

Airfoil

Gentlemen. Sorry to divert attention away from fuel for a moment

I have trawled through this massive thread and this fact does not appear to have been picked up, with regard to the credit the crew received for their "quick thinking", for reducing the amount of flap at the last moments.

I understand the command for a 'go around' was given, whereby the flap setting would be changed anyway from a landing configuration. If this is so, then the flap retraction and its subsequent benefit, was by default.

Was the command "go around" given?

I doubt it, given the situation was a developing undershoot being caused by a lack of power, despite firewalling the thrust levers. What would you "go-around" with at this point?

Not all go-arounds require a change of flap setting, so a call could be "go-around" or "go-around flap X", depending...

Where
 

Poof, where did that information derive? It's reasonable, and I can't recall seeing it here. With a serious AoA problem and 108 knots @ 200 feet, I think we can say it was an "unstabilized" approach, demanding GA. The 108 knots happened under A/P, so the GA command is definitely something to entertain, whether it happened or not, I think is unknown to most.

Airfoil

Correct Airfoilmod, the Grumman report does show temps in F. By conversion, the lowest freeze point they identified was -61C. (Interestingly, the highest freeze point they measured would have been off spec for Jet A-1on that parameter!)

Regarding your point about mixed units, both the prescribed test method for freezing points and Defstan Jet specs both specify the measurements to be in degC.

No! But the FCOC and filter are 'part and parcel' one assembly. The fuel temperature is raised prior to reaching the FCOC as it has already passed through the (LP centrifugal pump) side of the combined engine driven fuel pumps.

apologies for the poor picture!

http://img.photobucket.com/albums/v4...titled-1-1.jpg