Re: 2 engines vs 4 engines planes

From:         rdd@cactus.org (Robert Dorsett)
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date:         02 Nov 93 00:38:06 PST
References:   1 2 3
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In article <airliners.1993.696@ohare.Chicago.COM> drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard) writes:
>
>Your own anecdotes show that no matter how many engines the airplane had,
>it would not have been sufficient.  As many of you may recall, when an
>airplane flies through a cloud of volcanic ash (which does not show up on
>radar by the way), it takes all of the engines it has with it through that
>cloud, none are excluded.  I might also point out that a faulty maintenance
>procedure affects all of the engines, again regardless of their number.

But in the specific case of volcanic ash, there have been numerous incidents
where *all* engines have been lost, but only two or three were restarted.
In addition, those two or three were usually severely damaged, operating 
at diminished power.  


>>At the time of the BA 747's little problem, my father was project manager
>>for 747's at BA.  Up to that incident BA had been considering removing the
>>air turbines from the planes as they were not used.  At least that idea
>>got canned.  Incidentally, that plane has never been the same since.
>
>The 747 has never had ram air turbines.  The system is not designed to need
>one

I read his comment as referring to the air-driven pumps.  These are distinct
from the engine-driven pumps, which require windmilling action.  In the case
of flying through a volcanic cloud, the engine pumps may not be available:
hence, the air-driven pumps provide sufficient back-up authority.  I'm not
aware of any plans to "remove them" from any -200's and -300's, though.
As far as I know, each hydraulic system is required to have two power 
sources, primary and primary/alternate.


>What exactly do you mean by 'that plane has never been the same
>since'?  

Not to answer for him, but on the 747-400, two of the air-driven pumps
have been removed, replaced with electric pumps.



>>The 777 gives me nightmares.  How many people do we have to kill before
>>the airlines stop this crazy quest.
>
>It might be useful to ask how many have already been killed in the quest
>for ETOPS.  
>
>The answer is none.  Not a single person.

You can ask the same question about three and four-engined jets, too.  
And come up with the same answers.

But the big change in this new ETOPS race (A330 vs. 777) is that the target
market is the Pacific, not the relatively sedate North Atlantic. They don't
call it the rim of fire for nothing. :-)

WHEN we lose our first twin in some mid-oceanic disaster, we'll have to 
ask ourselves whether the long- term economic advantages were worth the 
lives of 200 or 300 innocent people.

Personally, I would think long and hard before flying across the Pacific on 
a twin.  I think that trijets are a much better compromise.  It's a shame 
that the L-1011 flopped.


---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd