(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” !