--- Henning Mortensen <henning_work@...
> Or one could look at it this way.http://www.guardian.co.uk/comment/story/0,3604,551036,00.html
> Let us also just underline that 4 aircraft capable
> of carrying over 300
> people each and each carrying up to 90,000 litres of
> aviation fuel were
> carrying less then 300 people.
> Clearly our use of aircraft has gone from the
> sublime to the ridiculous.
> Note, I may be wrong about the specific 767 model
> which was used. This may
> alter these numbers somewhat but not the underlined
> message of what amounts
> to a criminal waste of a precious resource, with all
> the attendant
> greenhouse gas repercussions.
> All this said, my sorrow and sympathy for the
> victims and their families is
> Another View
> Henning Mortensen
> Regina, Sk, Canada
When the news of the number of passengers on board
each of the four flights first came out, I also
noticed the low passenger loads.
There are three reasons flights with low loads are
1) If a plane is scheduled to fly A to B to C, and
there is a high load for the B to C flight, the plane
still needs to fly A to B regardless of how few people
are on board. Large airlines have a few spare
aircraft at their hubs, but those are reserved as
2) The schedule needs to be met as much as possible.
Weather and air traffic congestion already wreak
enough havoc on the schedule as it is. Cancelling all
flights with low loads would just make it worse. I've
never heard of a train being cancelled just because
there aren't enough passengers, so this is not just an
3) Similar to 1), even if a plane isn't scheduled to
fly another flight that day, the aircraft and a crew
are scheduled to fly somewhere the next day. Having
planes and crew in the wrong places overnight makes it
more difficult to operate the following day. Or, if
the plane is scheduled for maintenance the next day,
the plane has to be at an airport with maintenance
facilities. Otherwise, it would have to be flown
empty to a maintenance location (a "ferry flight"),
which is even more of a waste of fuel, since you are
guaranteed to carry zero passengers.
Since fuel costs money, airlines try to burn as little
fuel as possible. They load just enough fuel on each
flight to fly to the destination, plus the legally
required reserve. They have on-board computers to
calculate the most fuel-efficient cruising altitude.
Some airlines have retired almost all their old,
fuel-guzzling planes and replaced them with brand new,
fuel-sipping planes. New planes cost a lot of money
and take time to get them delivered, which is why you
still see old planes flying. But every airline with a
long-term horizon has a fleet replacement plan.
Tuesdays, Wednesdays and Saturdays are the three days
of the week with the lowest loads. Airlines often
have sales valid only for those days, in an attempt to
smooth out the demand over the seven days of the week.
However, as in any network, it is impossible to
smooth out demand perfectly.
On the other hand, airlines could have aircraft that
fly only on Sunday, Monday, Thursday and Friday (the
busy days). However, that means those planes sit
around and do nothing the other three days of the
week. An aircraft costs the same to buy (and it's a
lot of money) whether you fly it three or seven days a
week. You see the same thing with Amtrak. Their New
York to Washington schedule is the same Monday through
Friday, even though demand is higher on Friday than it
is on Wednesday. Buying a locomotive and several
coaches but using them only two or three times a week
is a waste of capital.
It is apparent to me that the terrorists chose flights
with low loads, to reduce their chances of passengers
fighting back. So far, there has been no evidence of
guns on board, so it was only a matter of the number
of other people on board.
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