From: (Robert Dorsett)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         21 Oct 96 02:51:37 
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In article <airliners.1996.2116@ohare.Chicago.COM> (C. Marin Faure) writes:
>In article <airliners.1996.2014@ohare.Chicago.COM>, (Robert
>Dorsett) wrote:
>> In article <airliners.1996.1975@ohare.Chicago.COM>
>(C. Marin Faure) writes:
>> >
>> >There aren't any risks, any more than there are on any flight in a modern
>> >commercial jetliner.
>> There are more risks, hence the operating and regulatory requirement imposing
>> extraordinary crew, airframe, maintenance, and dispatch procedures for ETOPS
>> operations.
>The original question was is an ETOPS flight riskier than a flight on a
>three or four engine airplane?  The answer is still no,

You still have not supported your position.  All you have stated is that
there are more risks to control, hence the overall threat to a passenger
is the same or more minimal than on a conventional airliner.

As a devout believer in Keep It Simple, Stupid, I would argue that a complex
network of checks and balances imposes its own risks, which can't be

The industry is not pushing ETOPS out of the box because it is inherently
safer.  It is pushing it because it is a cheaper way of operating airplanes.
Fewer heavy components, cheaper maintenance, cheaper labor, cheaper
operations.  Let's not lose sight of that, eh?

>First, the dust incidents.   You've proved my point.  ALL the engines on
>the four engine planes shut down, and ALL of them were damaged to some
>degree, so at that point it didn't make much difference how many there

In the incidents I'm familiar with, there were complex failure modes
involving severe damage to hydraulic, pneumatic, and thrust systems (and
in the case of the KLM 747-400, I recall, the APU, too).  My point is that
at least some engines were re-lit, thus providing the ability to maintain
the systems.

>Three and four engine airplanes don't have three or four engines simply as
>a margin of safety, they have three or four engines so they can get off
>the ground and STILL MEET the required margins of safety.

I'm not discussing takeoff or landing.  I'm discussing the real world
in the middle of the Pacific Ocean.  That's one BIG body of water, btw.

>margins of safety that apply to twin engine airplanes, by the way.  If a
>twin loses one engine on takeoff, its remaining engine has to provide
>sufficient power to safely continue the takeoff.  That's the rule.  Ride
>in a 757 sometime and you'll experience the result of having to have
>engines that are capable of continuing a takeoff after an engine failure.

So it's a chipper performer whenever everything's working.  How's it feel
when one engine goes out?

>> The problem is, you lose one engine, you've lost half your redundancy.
>> You lose two in a 747, you've lost half of your redundancy.  You lose
>> two in a 777, you're going swimming.
>The problem is that you're doing what so many people continue to do-
>focusing on the engines.  The engines these days are so reliable (I've
>seen the current data on the numbers of in-flight shutdowns of today's
>high-bypass fanjets on all airplanes regardless of the number of engines,
>and believe me, it's a tiny number), that they're almost not a factor in
>airplane reliability anymore.

What is almost?  0.1% of operations involve a shutdown?  0.01?  0.0001% In
real terms, what, 5-7 per year?  The fact is, you lose an engine in a 747,
you can probably proceed to destination.  It's an abnormal procedure.
You lose one in an ETOPS aircraft, it's a balls-out emergency until you're
safe on the ground again.  You have lost half your redundancy.

Robert Dorsett                         Moderator, sci.aeronautics.simulation