'Ice in fuel' caused BA jet crash
Mystery Flyer
"This was likely to be about "changes in procedures for pilots to follow
in certain cold weather conditions" as well as "changes in certain fuel
procedures on the ground", he said. "
According to BBC news.. Does this mean 777's must fly in warmer air?
Does that affect any particular route viability?
mf
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JF Mezei
> http://news.bbc.co.uk/1/hi/england/london/7598267.stm
I browsed through to www.aaib.gov.uk interim report.
For flights that are known to operate in very cold weather for long
periods, could they not draw fuel from wings first and finish up with
central tank ? This way, the fuel used toward end of flight wouldn't be
so cold and avoid the problem of this BA accident.
Would there be any cargo penalty or other performance issues of having
empty wing tanks and a full centre tank ? (since wing box would then
have to transfer more weight between lift-producing wing and the heavier
fuselage)
This report, in my opinion, failed to put emphasis on the fact that
there were 2 identical failures occuring at nearly the same time on this
flight. (each engine failed independantly of each other, from different
fuel tanks, and fuel lines and fuel pumps, and failed within seconds of
each other).
To me, this indicates that it is a systemic problem that should be
reproducible with the same conditions.
And while they may have fuel temperatures from the tank at the time of
failure, wouldn't ambiant air temperature at the plane's approach
altitude and time spent there also be an issue ?
If the plane had landed at a caribeean airport after circling it at idle
for 30 minutes versus a direct landing at London in midwinter
temperatures (which I assume would be between 0C and +5C at FL10 ?)
would things be different ?
AKA: if you spend enough time at near idle thrust in warm temperature,
ice might fall off the surface of pipes, partially obstruct flow, but
have time to melt before pilot requests additional thrust for final
approach. But if you descend directly into an airport in colder weather,
the ice would just fall off and not have time to melt, so by the time
you request more thrust, you still have ice blocking the way.
Perhaps this problem is more common, but in the few instances of fuel
getting that cold, the blockages have always had the time to melt before
final landing where additional thrust is needed, bit in this particular
case, there wasn't enough time and the system was still clogged at time
of final approach.
.
JF Mezei
flies the 777.
He said that the 777 cannot empty its wing tanks before emptying the
centre one, the wings would bend too much (light wings supporting heavy
fuselage).
Is that truly the case ? I would have expected the wings and wing box to
be designed to support full load of fuselage no matter how much fuel
there was in the wings.
What if the flight is a short haul needing only partly filled wing
tanks, but fuselage heavily loaded with heavy cargo and no fuel in
centre fuel tank ? Wouldn't that be the same as a long haul flight where
some cargo is replaced with fuel in fuselage ?
This particular pilot did not seem to believe the AAIB theory of ice
accumulating on walls of pipes and being released when throttles (fuel
flow) increased and then clogging some filter. His carrier has not
changed flight procedures for long polar routes on its aircraft. He
mentioned that there are many such flights every day and such problems
never encountered.
Anyone heard any other rumours on that BA flight accident ?
Uli
> He said that the 777 cannot empty its wing tanks before emptying the
> centre one, the wings would bend too much (light wings supporting heavy
> fuselage).
>
> Is that truly the case ? I would have expected the wings and wing box to
> be designed to support full load of fuselage no matter how much fuel
> there was in the wings.
>
i do not know the specific limitations of the 777, but basically, this is
true.
if you place the weight of your structure and load (both payload and fuel)
where your lift is, you need less structure (i.e. weight) to transfer
forces between these locations, e.g. the downward pulling weight of the
fuselage to the wings whose lift is oriented in the opposite direction.
from this point of view, flying wings are the best solution (there are some
other reasons why most airplanes use fuselages and empennages anyway...)
it's up to the design enigneer to set the airplane's limitations regarding
it's mass distribution. when looking at single engine motorplanes, you'll
find only the maximum flying weight as limitation in most cases. however,
in the cases of gliders and larger aircrafts, it may save quite some weight
or solve structural problems if you limit the fuselage weight to some value
lower then the maximim flying weight; this may be called "mass of
non-lifting parts" or "maximum zero fuel weight" or something alike.
> What if the flight is a short haul needing only partly filled wing
> tanks, but fuselage heavily loaded with heavy cargo and no fuel in
> centre fuel tank ? Wouldn't that be the same as a long haul flight where
> some cargo is replaced with fuel in fuselage ?
>
from an economic point of view, it may be desirable to load the airplane
like that in a specific case.
but i asume this is an ecxception. you have to stay within the limits the
aircraft's been designed and certified for. in a case like that, you might
ask the question if you chose the chose the right aircraft for that
purpose...
cheers,
uli
matt weber
>flies the 777.
>
>He said that the 777 cannot empty its wing tanks before emptying the
>centre one, the wings would bend too much (light wings supporting heavy
>fuselage).
>
>Is that truly the case ?
engines are probably from the Wing tanks. So they only way you can
use the center tank fuel is by moving it to a wing tank! IN addition
the only way to get to high TOW's is by filling the wing tanks. That
is where most of the fuel carriage is anyway, and odds are, you can
only burn fuel that is in a wing tank due to the pluming issues.
I would have expected the wings and wing box to
>be designed to support full load of fuselage no matter how much fuel
>there was in the wing.
In a 777-200, the only fuel storage IS in the wing. Only the -200ER,
and up have a center fuel tank.
Even then, about 66% of the fuel capacity is in the wing tanks.
If you load the aircraft up to MZFW, filling the wing tanks will
pretty much take you to MGTOW.
MZFW is 430,000 pounds. If you fill the wing tanks (207,000 pounds
usable), you are up past MGTOW in most configurations.
The 777-200ER is an unusual beast in that you almost ALWAYS have to
trade fuel for payload.
The tankage is huge.
Most 777-200ER's are about 630,000 pounds MGTOW, some are larger, and
some are smaller. The very high MGTOW's are difficult to use because
they come with serious Center of Gravity limitations if you have to
use all of the available MGTOW.
In any case, spec OEW is about 305,000 pounds, usable fuel is about
303,000, and total fuel is probably about 305,000.
Fill the tanks, and you have used up 610,000 pounds out of 630,000
pounds of MGTOW. That leaves you with ability to carry about 80 pax
and bags! The reality is full tanks in the 777-200ER is a ferry only
configuration. After the first 20,000 pounds of payload of so,
every pound of load takes a pound out of the usable capacity of the
center tank!
>
>What if the flight is a short haul needing only partly filled wing
>tanks, but fuselage heavily loaded with heavy cargo and no fuel in
>centre fuel tank ?
Cannot really happen. Most widebodies have a huge asymmetry in the
MLW and MGTOW. So in a short haul configuration, even if you load the
aircraft up to maximum zero fuel weight, you cannot load a lot of
fuel, so the aircraft will be pretty light.
MGTOW as I said is typically about 630,000 pounds on a -200ER,
MLW is 460,000 pounds, and MZFW is 430,000 pounds, so if you fully
load the aircraft, you shouldn't be landing with more than 30,000
pounds of fuel aboard, so for short missions, the aircraft cannot get
anywhere near MGTOW, or anywhere near filling the wing tanks let
alone the center tank. There is a big chunk of MGTOW that can only be
used for fuel that will burned on the mission.
> Wouldn't that be the same as a long haul flight where
>some cargo is replaced with fuel in fuselage ?
As I said in a 777-200ER, almost all payload comes at the expense of
fuel carriage.
The big difference in the -300ER/200LR is the increase in MGTOW,
which allows you to carry about 100,000 pounds of payload before you
have to start trading payload for fuel. There is a little fuel more
capacity than the -200ER, but the big thing is the increase in MGTOW
actually allows you to fill the tanks most of the time, and that
provides the range.
>
>
>
>
>This particular pilot did not seem to believe the AAIB theory of ice
>accumulating on walls of pipes and being released when throttles (fuel
>flow) increased and then clogging some filter. His carrier has not
>changed flight procedures for long polar routes on its aircraft. He
>mentioned that there are many such flights every day and such problems
>never encountered.
>
>Anyone heard any other rumours on that BA flight accident ?