At 1250 (the accident was at 1242)

EGLL 171250Z 20013KT 9999 BKN008 10/08 Q0996 BECMG 24018G28KT SCT012
BKN020

so clearly the weather wasn't a factor.

Jack

wrote in message
...
At 1250 (the accident was at 1242)

EGLL 171250Z 20013KT 9999 BKN008 10/08 Q0996 BECMG 24018G28KT SCT012
BKN020

so clearly the weather wasn't a factor.

Jack

Are there precise met circumstances where you do and don't get wind shear or
CAT ? I wonder if it was due to vortex shedding by previous craft like that
USA crash 5 years or so ago, packing them in too close.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Are there precise met circumstances where you do and don't get wind shear or
CAT ? I wonder if it was due to vortex shedding by previous craft like that
USA crash 5 years or so ago, packing them in too close.

The term CAT (Clear Air Turbulence) means just that, no cloud nor
ground induced turbulence.

Vortex shedding is normally only a factor when there are fairly calm
conditions (eg cold, calm early morning) or at altitude - it was
probably too windy today.

Windshear could occur in conditions such as today.

However, the circumstances of the accident are now becoming clearer
and not weather related.

Jack (retired airline captain)

wrote in message
...

However, the circumstances of the accident are now becoming clearer
and not weather related.

Jack (retired airline captain)

Bird strike? Fuel related problem?

David Haggas wrote in message
news

wrote in message
...

However, the circumstances of the accident are now becoming clearer
and not weather related.

Jack (retired airline captain)

Bird strike? Fuel related problem?



I thought the point of a glide-path approach was that it is a glide, not
only low propulsive power but air brakes as well to reduce airspeed. So as
long as the airframe stays balanced, no airframe breakages etc then it
should glide in unless someone or something intefered with the control
surfaces.

On 17 Jan, 17:51, "N Cook" wrote:

I thought the point of a glide-path approach was that it is a glide, not
only low propulsive power but air brakes as well to reduce airspeed. So as
long as the airframe stays balanced, no airframe breakages etc then it
should glide in unless someone or something intefered with the control
surfaces.

Sorry but you haven't got it quite right. There is no quick
explanation, but the term "glide path" is a technical term and no
doubt confusing to the layman. The glide path is flown with power and
is (normally) a 3 degree approach angle, ie approximately 1 in 20.
Power is needed all the way down. Indeed, student pilots learn the
mantra "speed with the stick (control column), rate of descent with
the power". Don't forget that flaps will be used (to keep the touch
down speed sensibly low) and this in itself increases the drag so
requires more power. A true glide approach without any power would
need a steeper angle (unless perhaps a flapless approach - not
recommended for other reasons).

It's a complicated subject and requires some in-depth knowledge.
Pilots undergo significant training to understand all the interactions
between power, flap setting, airbrakes, etc.

Jack

wrote...

It's a complicated subject and requires some in-depth knowledge.
Pilots undergo significant training to understand all the
interactions
between power, flap setting, airbrakes, etc.


.... whatever, this pilot deserves great respect! I know they get a lot
of training for this sort of thing in the simulators, but it's another
'ball-game' entirely when it actually happens at the end of a long
flight from the other side of Asia! Indeed, it sounds as if the entire
crew (cabin and flight-deck) deserve a huge pat on the back.

Martin.


--
Martin Rowley
E:
W: booty.org.uk

Martin Rowley wrote:
wrote...

It's a complicated subject and requires some in-depth knowledge.
Pilots undergo significant training to understand all the
interactions
between power, flap setting, airbrakes, etc.


... whatever, this pilot deserves great respect! I know they get a lot
of training for this sort of thing in the simulators, but it's another
'ball-game' entirely when it actually happens at the end of a long
flight from the other side of Asia! Indeed, it sounds as if the entire
crew (cabin and flight-deck) deserve a huge pat on the back.

Absolutley - one of the radio news quotes was 'the pilot deserves a medal
the size of a frying pan', I agree, along with the rest of the crew!

On 17 Jan, 14:40, "Jack )"
wrote:
At 1250 (the accident was at 1242)

EGLL 171250Z 20013KT 9999 BKN008 10/08 Q0996 BECMG 24018G28KT SCT012
BKN020

so clearly the weather wasn't a factor.

Jack

On another thread, a knowledgeable jet pilot has surmised :

I suspect that the first point of investigation will be fuel waxing,
caused by exceptionally low temperatures en-route from China. The
temperature at FL380 was around -70C for much of the last two or three
hours of flight. The fuel regularly uploaded in China is Jet A1, which
has a freezing point of -47C. With skin heating, the Total Air
Temperature (TAT) (the ambient air temperature as modified by skin
heating) would have been around -50C. The B777 tanks are a little
better insulated than ours, but the fuel temperature would have been
below -40C, I suspect.

Whether this would cause a problem would depend on the rapidity of the
descent and how much opportunity the fuel had to warm up as the TAT
rose. The tendency to wax would also depend how much water was present
in the fuel (there's always some). Water drain checks would have been
carried out in Beijing, but it wouldn't be the first time they hadn't
been carried out correctly, or that insufficient water was drained.
The effect of fuel waxing is pretty instant when it happens: a friend
of mine lost all four engines on a Hercules from this, back in 1982.
Luckily for him, he was in the tropics and the fuel was able to heat
up sufficiently in the descent for a disaster to be averted - but not
by much. They decended from FL270 to 5000' in the process of
recovering the engines.

The point would obviously be raised, 'why did this not affect anyone
else?'. The answer may be one or more of many things, including
technical factors within the aircraft, as well as its individual
flight profile in the descent.

So perhaps the weather in a different place may have had an effect ??
What would usual temps at that flight level be ?
And what variation may be expected ?

Anyone know ?

On Sun, 20 Jan 2008 13:26:50 -0800 (PST), TimHenderson wrote in


At 1250 (the accident was at 1242)

EGLL 171250Z 20013KT 9999 BKN008 10/08 Q0996 BECMG 24018G28KT SCT012
BKN020

so clearly the weather wasn't a factor.

On another thread, a knowledgeable jet pilot has surmised :

I suspect that the first point of investigation will be fuel waxing,
caused by exceptionally low temperatures en-route from China.

I doubt very much waxing was a factor as the engines still had power up to
two miles away and a height of only 600 feet. My money is on the engine
electronic control systems and particularly the associated software which
seems to have stopped manual override.

--
Mike Tullett - Coleraine 55.13°N 6.69°W posted 20/01/2008 22:36:33 GMT