Re: 2 engines vs 4 engines planes

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         06 Nov 93 00:24:37 PST
References:   1 2 3 4
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In article <airliners.1993.706@ohare.chicago.com>,
Pete Coe <pete@frosty.rational.com> wrote:
>Oh joy! My first flame!!!

It is not my intent to start or even participate in a flame-fest.  If that
is all that is driving this, lets take it to email. 

>I wasn't trying to say that a 767 would have been worse of in this example.
>Just as with the 747 all engines would have failed.  But would both engines,
>or even one, because I don't think that all 4 of the 747's were still
>running at touch down, running at very reduced power settings been enough
>to keep the plane in the air.  This was a fairly unique occurence, an act of
>god so to speak, the only thing that kept the 300 people or so alive was 
>that the plane had an adequate amount of redundancy for this situation.  We
>will never know if a DC10, or a 767 would have been up to this scenario.

You are certainly entitled to an opinion.  However, a great many people
have worked very hard to ensure that a 767/A310/You-Name-It will indeed
survive such incidents.  And not all of us share your opinion.

>>I might also point out that a faulty maintenance
>>procedure affects all of the engines, again regardless of their number.
>
>And isn't it part of ETOPS certification that both engines are maintained
>by seperate crews, to prevent common mode failure.  This as a direct result
>of the Eastern L1011 incident.
>
>>To throw a bit more light on the commercial aviations concern with safety,
>>I would like to mention that many airlines immediately replace one of the
>>engines on a brand new airplane to avoid problems such as mentioned above.
>
>So what.

So you might take a look at what your wrote above.  We said exactly the
same thing in different manners.  Airlines change engines to prevent, as
you put it, "common mode" failures.  This, like having different crews
maintain different engines on the same airplane, are all a part of air
transportation technology.  And the technology is getting better.  As we
learn, we incorporate our new knowledge into better products and services.

>Just to prove I am not playing favorites, the A330 worries me as well.

This isn't a discussion about manufacturers, but about twin engine long
range operations and their relative safety when compared to operations of
aircraft with more than two engines.  I assumed that you were not biased
against any one manufacturer.

>>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.
>
>Good.  But by the time it does happen it will be too late to turn back.  
>The airlines and manufacturers are now a huge political lobby.  When the 
>first ETOPS plane ends up in the water 100's miles from the nearest land do 
>you think ETOPS will be banned?  Of course not!  But if we said now that all
>long over water flights must be flown with 3 or more engines we might save a
>few hundred people.

A comprehensive study was performed by Dr Weener (Director of Safety here
at Boeing and on one of the technical committees of the AIAA) which showed
that the primary risk factor is the number of takeoffs and landings, not
how many engines the airplane was equipped with.  An ETOPS flight reduces
risk by reducing the number of takeoffs and landings associated with
flights to a given city pair.  Fine you say, but a 747 can do the same
flight with more engines.  You are correct.  However, it cannot provide
that service economically.  That is, not enough people hold your same
opinion to a degree that would force them to pay for the higher priced
ticket.  The overwhelming majority of people who fly are price driven.
That is, the cost of the ticket is the single largest criterion applied to
the purchase decision.  No ticket purchases - no service.  Therefore, an
ETOPS flight can allow airlines to offer city to city service that would 
not normally be available except as a multi-stage flight, which has
the higher risk of an accident.

I believe a correct interpretation of the data indicate that ETOPS flights
allow safe, cost-effective transportation options that would not otherwise
exist.

>>>  Although I am myself a professional
>>>in the aviation industry, I consider myself to be well informed.
>
>>I would dispute that.
>
>Opinions differ.  Lets compromise on fairly well informed.

Fair enough.

>Just to finish off.  I have already said that ETOPS Is a bad idea.  I am not 
>enough of a tabloid reader to believe that if I set foot on a 767 transatlantic
>flight that I am automatically going to die.

Good for you.

>      Its just that all things been 
>equal I would rather be on an aircraft with more engines.  It's the same as 
>other people saying that they avoid DC10's.  The statistics show that it is 
>safer than crossing the street, we are jsut trying to minimise the risk.

That is my point.  A more informed interpretation of the available data
would indicate that ETOPS flights are safer than flights in more-than-two
engined aircraft.  If your preference is to fly four-engined airplanes in
lieu of a twin on the same route, great.  I support your decision.
However, calling other people crazy for taking that same twin is not
helpful.  Nor is making uninformed assertions about safety in a public forum
after identifying yourself as an aerospace professional.

>The story of the last 20 years of commercial aviation is one of relentless
>cost cutting in the face of competition.  Some examples that worry me:
>
>ETOPS
>Two man cockpits on long haul flights
>Blocking over wing exits to add more seating
>Fly by wire
>Reduction of cabin air recirculation
>
>With the exception of fly by wire I would think that all of these have been 
>driven by the airlines not the manufacturers.  So I do not blame Boeing or 
>Airbus, they are just trying to gain market share.  It is up to us as 
>customers to vote with our feet, but as most people neither know nor care how
>many engines their plane has I know that the trend will continue.

I agree that the last 20 years have shown dramatic improvements in cost
reduction.  I have also seen the data and they show that the accident rate
dropped quite a bit (60% or so)  over that same 20 years.  In fact, we are
now to the point where we are trying very hard to understand accidents
that won't go away, like controlled flight into terrain, like the A320
that crashed into Mount St. Odile.  Or wind rotors and microbursts that
have caused numerous accidents.  Engine failure is not even of the
same order of magnitude as these other root causes.

Those other trends that you have noted above should be viewed as positive
developments.  They make it possible for the middle class American to fly
on long trips.  It wasn't that long ago that only Rock stars and the rich
could afford to fly.  Only since the early 1970s has the common, everyday
person been able to afford an airplane ticket.  Not only is air
transportation fast and affordable, it is also very, very safe.  Men and
women just like me put in many many hours to make sure that things just get
better.

["Yes, well."  The short dumpy engineer steps down from a rather tattered
looking soap box, straightens his lapels, gathers his materials together
and walks out of the room - carefully shutting the lights off as he leaves]

-- 
Terry
drinkard@bcstec.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."