M.Mouse

Fascinating stuff. Great that you have access to the final report which explains your statement.

It would be useful to know when the rest of us will be able to read it as well.

phil gollin

The heater exchange mods are only valid for a set of unrepresentative tests.

The tests themselves raised supposedly previously unknown behaviour of fuel/water mixtures (?????).

SO;

1: They still need to carry out representative tests (of whatever sort) which cause the engine problems or otherwise explain the engine failures by suggesting different fuel conditions from those extrapolated from the evidence.

2: IF there is this previously unknown behaviour of fuel/water mixtures then ALL - REPEAT ALL - certification authorities and ALL - REPEAT ALL - airframe/engine combinations need to be re-checked to see if they are immune from these effects.

Strangely enough it is the second of the above that I have more problems with. I await the final (or third interim) report with interest.

tanimbar

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

In support of Phil Gollin's comments ....

The critical issue arising from the crash of BA038 is starkly worded below (from the AAIB interim report (Water ice in fuel, p12)),

Either the AAIB made a mistake in this claim or the industry has an immense problem. Either way the AAIB's final report will be very interesting.

Regards, Tanimbar

Landroger

I feel obliged to make the same disclaimers as Tanimbar, although for scientist read engineer - non aero. Nevertheless, I have followed this thread since the day the accident happened, indeed it was the real reason I joined this forum. Mainly because of the almost unheard of bilateral engine 'failure', which from an engineer's point of view is the equivalent of a good 'whodunnit' - better by miles than the Davinci Code. Yes, I know the engines didn't actually fail; failed to respond is a better phrase, but that doesn't get round the fact that both of them did it at the same time.

I have read as much of the linked information about ice carried in fuel and the tests carried out as I could. I have read every linked pronouncement from the AAIB and I have, as I said, read every post in this thread, looking for the little nugget that stops my engineering alarm bells ringing. And the oil heat exchanger on RR Trent option aeroplanes didn't do it for me. I tend to agree with Phil Gollin and Tanimbar, that the case for the heat exchanger is, at best, unproven.

On the other hand, one could - as I often do in my day job - apply the principle of Occam's Razor and say that since this is the simplest explanation, we should not strive too officiously to find another. However, the heat exchanger issue appears to have been addressed and there is very, very little other forensic evidence either way, what if it is not the culprit ..................

Roger.

bearfoil

This topic is well covered here. Simply put, The 'fix' piggybacks a thermodynamic demand on the FOHE to melt ice accumulation. This is not a function of the original design, and mods to the OE unit don't resolve questions that have been asked early and often in this thread by fuel engineers, pilots, and others. Period.

The rest is politics, wishin' and hopin'.

bear

lomapaseo

Unknowns are just that. They do not necessarily signify an immense problem.

They are expected to be accounted for as part of the underlying risk in our lives for anything that we design. It's the knowns that we apply processes to address.

I don't expect the AAIB to solve the problem, but leave it to the industry (manufacturers and regulators) to reduce the degree of the unknowns in this regard.

CONF iture

Blocked FOHE, blocked PITOT ...
Ice crystals : last threat in the sky ?

Hydroman400

I don’t fully agree with your statement regarding the intention of the original design. The FOHE is used to heat the fuel for ice protection. The FOHE forms part of the engine Thermal or Heat Management system, which to quote the Rolls Royce engine book “[I]A responsibility of the heat management system is to ensure that the fuel temperature is above 0 deg C at the critical and vulnerable parts of the fuel system for the majority of operating conditions. The heat rejected by the engine oil system via the FOHE is normally sufficient to ensure fuel temperature above 0 Deg C, so protection the fuel system from fuel-borne ice.”

I recall that Boeing has made it’s own investigation on the issue (white paper) and seem to believe that the reason that the other B777 engine (PW) has not suffered similar events is due to the engine fuel system architecture; warm spill flow from the FMU is re-introduced upstream of the FOHE and therefore warms the colder fuel coming from the aircraft fuel tanks, before it contacts the face of the FOHE.

It must be noted that the RR Trent 800 does not re-introduce warm spill flow upstream.

I wonder if a further modification for future RR engines will change this philosophy instead of removing tapered ends of the FOHE tubes…….

bearfoil

Hydroman400

To me, the way fuel ice is addressed via FOHE is backwards, and under conditions that were 'tested' by Boeing, show the concept lacking. Now the inability to 'de-ice' ice laden fuel is patent, per the reports and the extensive work done by the manufacturer, though it too is not dependable. Delta rolled back at 35k feet and lost 5k to regain thrust. At those frigid temps. the FOHE is shut down, and the oil is 'cooled' by air cooler. At take off under high demand, the oil heats rapidly, and the fuel cools the oil. Let down or cruise are the problem, under these conditions, the Exchanger is inop. In other words, even a spill valve would be putting frigid fuel back to the face. The engine operation for the Trent does not mention "fuel de-icing", not in the a/c manual.

You have a most valid point, though I disagree with the ability of the unit to perform to RR's expectations, via its manual. A long discussion, but what we have here is an enhanced demand due to a surprise in fuel performance. This new demand is addressed by trimming tubes back to face sheet, instead of re-engineering a new unit (architecture); although a 'new' FOHE wouldn't necessarily be expected to mitigate the problem well, if at all, given that the fuel performance is still "mysterious".

bear

Hydroman400

When I mentioned spill flow, I was referring to the 'excess' flow from the HP gear pump, which due to compression and pressure drop across the regulating valve imparts an increase in the fuel temperature regardless of whether the fuel is acting as a heat sink for the FOHE. As the gear pumps provide flow proportional to the gearbox and hence NH speed, the available flow is always more than the required flow to maintain selected N1, EPR etc. This warm excess flow is then re-introduced upstream of the LP pump (impeller). What seems to be important is where it is re-introduced

I am in no way saying that the RR FOHE re-design will completely address the problem, as for now the complexities of the issue are not fully understood.

bearfoil

Hydroman

I have the schematics for both the Trent and GE somewhere in my computer, and I acknowledge your comment re: Boeing's note that RR has no upstream inflow of discharge from the Spill Valve. Another poster suggested that beyond the added heat issue of HP passage, the gears would additionally masticate any solid Ice in fuel that had passed through the tube matrix of the HE.

The salient question becomes, If this process ('Spill', 'Mixing') mitigates Fuel Ice in any way and remains unaddressed relative to upgrading the Trent, well, is the AD a "Palliative", mechanically and politically? Airfoilmod was on about re-engineering the architecture as well as the FOHE, and SmilinEd suggested Fuel Heat, a process Boeing has utilized in a/c that fly to 60k feet routinely. Severing the protruding tubes at the face sheet amounts to a "Subtraction", indicating that nothing new has been added to this system, and no substantial change has occurred.

In addition I would add that removing the extra length of the tubes eliminates an (inadvertent?) nesting area for some amount of ice accumulation of the type identified by Boeing as "Migratory". In this sense, I would suggest that the FOHE performance has been actually degraded relative to Fuel Icing caused rollback.

bear

G-CPTN

Beeb announcing that a report just issued gives the cause of the undershoot to be ice in the fuel . . .

BBC News - Heathrow BA plane crash caused by 'unknown' ice fault

PoloJamie

Formal report is on the AAIB's website, although the actual report's link is broken atm
Air Accidents Investigation: 1/2010 G-YMMM

dxzh

Try the following links:

http://www.aaib.gov.uk/cms_resources...20Synopsis.pdf
http://www.aaib.gov.uk/cms_resources...20Contents.pdf
http://www.aaib.gov.uk/cms_resources...ection%201.pdf
http://www.aaib.gov.uk/cms_resources...ection%202.pdf
http://www.aaib.gov.uk/cms_resources...ection%203.pdf
http://www.aaib.gov.uk/cms_resources...ection%204.pdf
http://www.aaib.gov.uk/cms_resources...Appendices.pdf
http://www.aaib.gov.uk/cms_resources...20Glossary.pdf

The_Steed

'Ice problem' in BA jet accident - MSN News - MSN UK

A breath of fresh air to have a report that is factual, concise and not full of exaggerations...

302B31

Link now fixed

phil gollin

I'm amazed.

I'll do my reply in a couple (or more) posts, the first a summary and the other(s) some extracts.

I have ploughed my way through the report and am extremely unimpressed.

I find the report extremely annoying.

The main reason is that whilst the FOHE (Fuel Oil Heat Exchanger) may be the main reason for the engine roll backs the report is amazing in the way it treats the causes (and testing).

It is amazingly obvious that they did/do not want to mention the actual water content of the fuel on the flight. It SEEMS to be mention only three times and almosy only in passing at "35 - 40" ppm, HOWEVER, all the tests were run with concentrations of 90 ppm (or more). There is no examination in detail of the actual measured water levels or what the actual state of the fuel/water mixture might have been like at the landing stage.

Also, the tests (at UNREPRESENTATIVE water content levels) were inconsistent and it would seem were never tried at more representative water content levels.

So, what did the tests show ???????

I don't know. It would seem that somehow unrepresentative tests are relevent and that the whole report should ignore the actual fuel/water conditions.

And as for the lack of future actions regarding the previously unknown phenomenum of the fuel/water slush with ALL other airframe/engine combinations that is just running away from a huge cost.

I am extremely disappointed.

phil gollin

(PART ONE of TWO)


One needs to read the whole report, however some highlights that I THINK relevant ;


AA:- From “Synopsis” ;

“2) Ice had formed within the fuel system, from water thatoccurred naturallyin the fuel, whilst the aircraft operated with low fuel flows over a long period ……..”

What does “naturally” mean ?


BB:- From “Synopsis” ;

“3)The FOHE, although compliant with the applicable certification requirements, was shown to be susceptible to restriction when presented with soft ice in a high concentration, with a fuel temperature that is below ‑10ｰC and a fuel flow above flight idle.”

Why just the “FOHE” here when they talk of the “fuel system” elsewhere ?


CC:- From “Synopsis” ;

“4) Certification requirements, with which the aircraft and engine fuel systems had to comply,did not take account of this phenomenon as the risk was unrecognised at that time.”

And how have thing changed now for ALL aircraft and engine combinations ?


DD:- From 1.11.2 ;

“….. As the DFDR record commenced, an active status message was recorded from the FQIS water detector located in the centre fuel tank (Figure 15). The status message remained active for five consecutive samples of that parameter: a total of five minutes and twenty seconds. After the pushback, the park brake was applied and the aircraft remained stationary for about three and a half minutes before taxiing. As the aircraft taxied, the levels of aircraft vibration increased. The water detector message remained active for a further 100 to 160 seconds before extinguishing; the exact time could not be confirmed due to the long period between successive samples of the parameter. There were no further indications from the centre tank water detector. There were no indications from the left and right fuel tank water detectors during the flight. ……..”


EE:- From 1.11.2;

“……Approach

As the flaps reached the 30° position the airspeed had reduced to the target approach speed of 135 kt and the autothrottle commanded additional thrust to stabilise the airspeed (Figure 20, Point A). In response to variations in the wind velocity and associated airspeed changes, there followed a series of four, almost cyclic, thrust commands by the autothrottle (Figure 20, Point B). It was during the fourth acceleration, and as additional thrust was being commanded, that the right engine, followed some seven seconds later by the left engine, experienced a reduction in fuel flow (Figure 20, Point C). The right engine fuel flow reduction occurred at a height of about 720 ft and the left engine at about 620 ft. Just prior to the reduction in right engine fuel flow, about 2.5 nm from the runway, the flight crew were visual with the runway and the co-pilot became pilot flying (Figure 21).

Of the four thrust commands it was the second that resulted in the highest delivery of fuel flow, reaching a peak of 12,288 pph for the left engine and 12,032 pph for the right (Figure 20, Point D). These peaks occurred about 26 seconds prior to the reduction in fuel flow to the right engine. Peak fuel flows during the first and third thrust commands were lower, at about 9,500 pph and 9,000 pph respectively.

During the fourth thrust increase, the right engine fuel flow had increased to 8,300 pph before gradually reducing. The recorded EPR then started to diverge from the commanded EPR and the right engine FMV opened fully (Figure 20, Point E). Some seven seconds later, the left engine fuel flow, which had increased to 11,056 pph, also started to reduce and the left engine FMV also moved to its fully open position (Figure 20, Point F). The QAR record ended shortly after. ……..”


FF:- From 1.12.4.2 ;

“……..Water Scavenge systems

The nozzles from all the water scavenge jet pumps were removed and examined on 2 February 2008 and the following discrepancies were noted.
When the nozzle from the right main scavenge jet pump was removed from its housing half a teaspoon of a ‘jelly‑like’ substance, later identified in a laboratory as “water”, was found in the housing. It is not known if this water was originally lodged in the nozzle and was pulled through the flap valve into the housing, or whether the water had been introduced into the housing during a previous maintenance activity. The water was tested for microbiological contamination and the quantity of contamination was assessed as negligible. ……..”


GG:- From 1.16.2.1 ;

“1.16.2.1 Fuel samples

Following the accident, 66 fuel samples were taken from the aircraft, and engines, and a number of these samples were tested by QinetiQ and another independent laboratory. ………………………………………………..”

…………………An explanation of the testing conducted on these samples and the results are detailed in Appendix C.

The fuel samples from G‑YMMM complied fully with the specifications for Jet A-1. The sampled fuel had a fuel freeze temperature of -57°C and water content of between 35 and 40 parts per million (ppm). …………”


HH:- From 1.16.2.2 ;

“…………….. It was reported in the AAIB Interim Report, dated 4 September 2008, that 71,401 kg of No 3 Jet Fuel (People’s Republic of China) had been loaded onto G‑YMMM at Beijing prior to the start of the accident flight. Since receiving this initial information the AAIB was provided with further documentation indicating that the fuel was Jet A-1, which had originated in South Korea and was shipped to Tianjin, China, before being transferred to the airport bulk fuel storage facility at Beijing.

The investigation was provided with a number of documents including the refinery test certificates, airport storage tank records, hydrant records and refuelling vehicle records. The Korean test certificate indicated that the fuel was compliant with Check List Issue 22, which ensures that the fuel meets the requirements of Defence Standard 91-91 and ASTM D1655. Quality assurance checks undertaken at various points on its journey to the aircraft showed no evidence of significant contamination of the fuel. Moreover, the properties of the fuel recorded in the refuelling receipt and quality assurance certificates were consistent with the test results for the fuel samples taken from G‑YMMM after the accident. ………..”


N.B. I would note that both here, and earlier in the Synopsis, opportunities for mentioning water levels and/or explaing likely water levels in the actual flight fuel are not taken.



II:- From 1.16.5.4. ;

A large section which again generally carefully avoids comments re. actual/perceived flight fuel water content, except for ;

“….. The repeatability of the test was such that with a water concentration of 100 ppm there was a 95% chance that the test would show a result between 76 and 124 ppm. ……”

“………. A target water concentration of 90 ppm (as defined in ARP 1401) was selected for all the tests. ……”

“………… using fuel conditioned with approximately 90 ppm of water and maintained at a temperature of -20°C, which was near the fuel temperature at which the rollbacks occurred on G‑YMMM and N862DA (refer to 1.18.2.1). ……..”

(But not the water level of the flight fuel)

“………… The only occasion when it appeared that there might be a sufficient quantity of ice to block a pipe occurred when approx 6 litres of water had been injected into the boost pump inlet over a period of 7 hours. During this period the flow rate was maintained at 6,000 pph and the water content varied between 100 and 150 ppm. ………”

“…….. -As little as 25 ml of water, when introduced into the fuel at an extremely high concentration17, can form sufficient ice to restrict the fuel flow through the FOHE.

17 The water concentrations in the fuel, when the water was introduced in the manner used in these tests, were of the order of 100 times the concentration levels specified in the certification requirements. …………”


JJ:- From 1.16.5.4

“………….Refuelling at Beijing

A test was run to simulate refuelling the aircraft at Beijing when fuel at a temperature of 5°C was added to fuel tanks containing fuel at a temperature of -20°C.

During the test a fresh batch of fuel at 10°C was added to fuel at a temperature of -22°C in the environmental tank at a ratio of 1/1. The boost pump was run for 25 minutes to provide pump cooling and motive flow for the water scavenge pump. Whilst a few ice crystals were observed floating in the fuel, there was no build up of ice either in the tank or on the boost pump inlet screen or inlet pipe. …….”

Note :- no mention of water levels


KK:- 1.16.5.4 ;

“…….. Water concentration

During the environmental tests the amount of water sprayed into the fuel was closely monitored to try and maintain the concentration at 90 ppm. Frequent fuel samples were taken throughout the tests and the water concentration was established by running at least two Karl Fischer tests on each sample. The results indicated that the water concentration in the fuel flowing through the test section of the rig varied between 45 to 150 ppm. The discrepancy between the metered and measured water content might be explained by ice collecting, and being released from the supply tank and the pipes being tested. However, it was also observed, from the results of several Karl Fischer tests carried out on the same sample of fuel, that the measured water concentration varied by up to 60 ppm. ……….”

(But as mentioned in “II” above the “repeatability” of these tests is questionable.)


LL:- 1.16.6 ;

“…… 1.16.6 Ice formation in B777 fuel tanks

Following the defueling and draining of G‑YMMM’s main fuel tanks, some fluid remained trapped between the stringers adjacent to Rib 8. Approximately 0.6 litre of fluid was removed, by syringe, from each main fuel tank and stored in a clean glass jar. The fluid settled into two distinct layers and was analysed by QinetiQ who confirmed that the 0.6 litre sample from the left wing included 0.2 to 0.25 litre of water and the sample from the right wing 0.1 litre of water.

To establish if the quantities of free water found in the dead space in the fuel tanks on G‑YMMM were normal, two of the operator’s other Boeing 777s were inspected after arriving from Beijing on 21 February 2008 and 17 March 2008. Access was gained to the main fuel tanks within 3 hours of the aircraft landing and while the fuel temperature was still below 0°C. On both occasions small amounts of ice were found adjacent to Rib 8, around the edge of the stringers in front of the forward boost pump inlet. The largest piece of ice, on both aircraft, had built up around the inboard of the tank hatch and measured approximately 14 cm x 11 cm x 3.5 cm. This ice was firmly attached to the bottom of the fuel tank. There was no evidence of ice or slush in the rear part of the tank; however there were small pockets of water in a number of locations along Rib 8. It is estimated that the total amount of ice and water was about 0.5 litres. From the distribution of the ice and water, it would appear that water collects and ice forms mainly forward of the front boost pump inlet where there are no water drain holes in the stringers. ……………….


MM:- From 1.18.1.2 to 1.18.1.4 ;

1.18.1.2 Water in aviation turbine fuel

Water is always present, to some extent, in aircraft fuel systems and may be introduced during refuelling or by condensation from moist air which has entered the fuel tanks through the tank vent system. The latter effect is greatest when a cold soaked aircraft descends into a warm moist air mass. The water in the fuel can take one of three forms: dissolved, entrained (suspended) or free water.

Dissolved water: Dissolved water occurs when a molecule of water attaches itself to a hydrocarbon molecule; the amount of water dissolved in fuel is a function of humidity, temperature and the chemical constitution of the fuel. As a general guide the dissolved water content of aviation turbine fuel in parts per million (ppm) is approximately numerically equal to the temperature of the fuel in degrees Fahrenheit. When warm fuel is cooled the dissolved water is released and takes the form of either entrained or free water.

Entrained (suspended) water: Entrained water is water that is suspended in the fuel as tiny droplets and may not be visible to the naked eye in concentrations below 30 ppm. At higher concentrations entrained water will give the fuel a cloudy or hazy appearance, depending upon the size and number of water droplets. Entrained water can be formed by the release of dissolved water as the fuel cools, by violently agitating water and fuel together, or if there is a surfactant in the fuel.

A surfactant acts to stabilise small water droplets so that they do not form large water droplets that would settle out on the bottom of the tank. The maximum amount of surfactant allowed in aviation turbine fuel is not directly specified in the fuel specification but is controlled by water separation testing as part of fuel delivery requirements.

Agitation can occur during refuelling, mixing of the water scavenge outlet with the bulk fuel, or as the fuel and water pass through the aircraft fuel pumps. Entrained water will settle out of the fuel, but the rate is dependent on the droplet size, the density of the fuel and theamount of fuel agitation. As a general rule, under static conditions, entrained water is considered to settle at a rate of about one foot per hour; however it is unlikely that on an in-service aircraft all the entrained water would have the opportunity to settle out of the fuel.

Free water: Free water is the water which is neither dissolved nor entrained and, as it has a higher density than the fuel, it takes the form of droplets, or puddles of water lying on the bottom of the fuel tanks. Free water can also be found in the fuel filters and stagnation points within the fuel delivery system.


1.18.1.3 Estimated water content of fuel on G‑YMMM

Based on the temperature of the fuel, it was estimated that the fuel loaded at Beijing would have contained up to 3 litre (40 ppm) of dissolved water and a maximum of 2 litre (30 ppm) of undissolved water (entrained or free). In addition, it was estimated that a maximum of 0.14 litre of water could have been drawn in through the fuel tank vent system during the flight to Heathrow. This water would have been evenly spread throughout the fuel and would have been in addition to any water remaining in the fuel system from previous flights. These quantities of water are considered normal for aviation turbine fuel.


1.18.1.4 Formation of ice in fuel

As water cools it freezes and forms ice as follows:

Dissolved water: Any water that is still dissolved in the fuel at low temperatures will not form ice because the water molecules are still chemically bonded to the fuel. Dust particles in the fuel could provide a nucleation point for the formation of water droplets that could then form ice. However, at low fuel temperatures the concentration of dissolved water is very low and therefore the amount of ice formed by this mechanism would be small.

Free water: Free water forms ice as it is cooled below its freezing point and within the aircraft fuel tanks the cooling mechanism is the effect of the TAT on the lower wing skin; it is the water closest to the wing skin which freezes first. From the examination of two other B777 aircraft, by the AAIB, it appeared that, in the main fuel tanks, ice forms around the rivets, access panels and structure adjacent to Rib 8 and it was very difficult to release some of this ice from the bottom of the tank. For the ice to release it is necessary to increasethe temperature of either the fuel or the lower wing skin above the melting point of the ice.

At the point, in the accident flight, when the engines did not respond to the demand for an increase in power, the fuel temperature was -22°C and the TAT was 12°C. Photographs of G‑YMMM taken as it crossed the airfield perimeter show the inboard sections of the lower wings skins, which form the main fuel tanks, covered in frost which indicates that the wing skin was very cold; therefore, there was no release mechanism for any ice that may have formed on the bottom of the fuel tank.

Entrained (suspended) water: Entrained water in fuel will freeze and form ice crystals, which turn the fuel cloudy. Because the density of the ice crystals is approximately the same as the fuel, the crystals will generally stay in suspension and drift within the fuel until they make contact with a cold surface. Due to impurities in the water the ice crystals will not start to form in the fuel until the temperature has reduced to around -1°C to -3°C. As the temperature is further reduced it reaches the ‘Critical Icing Temperature’ which is considered to occur between -9°C and -11°C. The ‘Critical Icing Temperature’, is the temperature at which the ice crystals start to stick to their surroundings. As the temperature is further reduced to -18°C, the ice crystals start to adhere to each other so that they become larger, with the risk of blocking small orifices.

The temperature range over which ice crystals in fuel adhere to surfaces, and each other, is sometimes called the ‘sticky range’. From observations made during the sub-scale testing, the investigation defined the ‘sticky range’ as being between -5°C and ‑20°C. …….”


(TO BE CONTINUED >>>>>>)

phil gollin

(PART TWO of TWO)



NN:- From 1.18.1.5 ;

“………. During this investigation very hard, dense ice was found in the bottom of the aircraft main fuel tanks and occasionally, during the testing, a thin layer of what appeared to be rime ice formed around the outlet of the boost pump check valve housings. However, for the most part, during the icing tests, the ice which formed within the fuel system pipes was very soft and could be easily moved around. Temperature variations did not appear to affect the type of ice that was formed. When the ice was melted it was found to contain a mixture of fuel and water.

To overcome the difficulties in maintaining the water concentration in cold fuel, the aircraft manufacturer fitted an acrylic box around the boost pump inlet and introduced a mixture of warm fuel and water into the cold fuel, through an atomising nozzle. Nitrogen was then blown across the nozzle to prevent the water freezing and blocking the holes. This produced ice crystals which had formed from a high concentration of entrained water, which would then adhere to the inside of the pipes. During the accident flight, the ice crystals would have formed from a lower concentration of entrained water. Some of this entrained water would already be present in the fuel and some would have formed as dissolved water was released as the fuel cooled. ………….”


OO:- From 2.5 ;

“……….. Water will always be present in aviation turbine fuel. At 35 to 40 ppm the total water content measured in the fuel samples taken from G‑YMMM was similar to that in the samples taken from another B777, G‑YMMN. The small quantity of water droplets found in the engine fuel filter housings was also similar. The quantity of free water found in the main fuel tanks on G‑YMMM, after the accident, was also similar to the quantity of free water found in the tanks of two other aircraft which had flown a similar route.
In summary, there was no evidence of excessive or unusual amounts of water in either the fuel or the fuel tanks on G‑YMMM. ……”


PP:- From Section 3 “Conclusions” ;

“……… Fuel

There was 10,500 kg of fuel remaining on the aircraft at the time of the 64. engine rollback, 5,100 kg in the left main fuel tank and 5,400 kg in the right main fuel tank.

The fuel onboard G‑YMMM was consistent with Jet A-1 and met the 65. Defence Standard 91-91 and ASTM D1655.

66. The fuel sampled from G-YMMM contained 35 to 40 ppm of water, which was similar to that found on other aircraft that had flown similar routes. ……….


QQ:- From Section 3 “Conclusions” ;

WARNING **** This I find very odd, if not actually mis-leading ! The “tests” were on fuel containing 90 ppm, which is not “normal” for operations, but is in the normal range for certain tests. There SEEMS to be no evidence to think that the fuel on board the flight even approached this “normal” concentration.


Fuel system testing

84 Ice can form within the fuel system feed pipes with normal concentrations of dissolved and entrained water present in aviation turbine fuel.



RR:- From Section 3 “Conclusions” ;

WARNING **** I.E. this report is supposition !

“……. 90. The properties of the ice generated during testing may not be the same as the properties of the ice generated in flight. ……..”


SS:- From Section 3 “Conclusions” ;

Other “classic” extracts (!) – which “forget” to mention that the comments are based on UNREPRESENTATIVE tests

“………92. Ice released from within the fuel pipes could form a restriction at the face of the FOHE. …….”

“……..93. Tests demonstrated that water when injected into a cold fuel flow at concentrations of the order of 100 times more than certification requirements could form a restriction at the face of the FOHE. ………”

“…….. 94. Sufficient ice can accumulate in the Boeing 777 fuel system, which, when released, could form a restriction on the face of the FOHE. …….”


TT:- From “Conclusions” ;

But having had “fun” criticising the report, it is important to note ;

“……. 97 The FOHE was the only component in the fuel system that could be demonstrated to collect sufficient ice to cause the fuel restrictions observed during the accident flight. ……..”


From Section 4 “Safety Recommendations” ;


“4.3 Safety Recommendation 2008-048: It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency should take immediate action to Consider the implications of the findings of this investigation on other certificated airframe / engine combinations.

4.4 Safety Recommendation 2008-049:It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency review the current certification requirements to ensure that aircraft and engine fuel systems are tolerant to the potential build up and sudden release of ice in the fuel feed systems.

This is the BIG ISSUE. The tests were unrepresentative and the icing phenomena not properly explained. What needs to be done is the science to understand the icing and ALL airframe/engine combinations tested.

Unfortunately recommendation 4.3 is only to “consider” not to act ! and 4.4 is only to “review” !

S.F.L.Y

No CVR transcription... Too bad, that would have been interesting to get a better understanding of these statements:

and

So the report mentions the succession of a "disconnection intent" followed by an "initial belief" which finally happened to be an "omission". I'm quite disappointed as I was expecting more information on the crew's management of this unusual situation.