I imagine it was the "precautionary principle" that guided the decision.
Viz:
All jet aircraft engines use essentially very similar designs.
We don't know how thick the ash is.
We don't know how much exposure to ash will cause an engine to fail.
We do know of cases where planes have flown through ash clouds and have had flame-outs of all engines.
We do know that if there is a cloud of ash in the approach path to a given airport we may be
exposing passengers to unacceptable risk of death.
So we had better shut down everything.
As John suggested, some Bayesian assessment of risks using all available data from previous incidents would be a start. Who knows what information there is out there?
Dick Brown
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>>> Bernard Torsney <[log in to unmask]> 4/23/2010 12:32 pm >>>
Is an assumption here that the 'tripled risk' holds independently for
each plane.
This seems unreasonable if the air traffic authorities concerns had some
substance.
So the theory was, given one plane falls down from an ash cloud, the
chances
that others do increases, rockets even(!).
Hence if there's lots of planes in the sky, lots might fall down -
and then there's all those on the ground on whom they fall.
Ben Torsney
-----Original Message-----
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[mailto:[log in to unmask]] On Behalf Of John Bibby
Sent: 21 April 2010 23:17
To: [log in to unmask]
Subject: Any volcano ash experts please?
The Civil Aviation Authority has no remit to minimise road-accidents, so
their recent Icelandic actions have been pretty sound.
However, does the gain from grounding airplanes even with a tripled risk
of
falling out of the sky exceed the potential loss from diverting dozens
of
thousands from a very safe form of travelling to road travel, which is
much
more risky?
Do we have a Bayesian methodology to quantify that potential gain or
loss -
and what about interval estimates?
JOHN BIBBY
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