Re: 2 engines vs 4 engines planes

From: (Pete Coe)
Organization: Rational
Date:         03 Nov 93 23:30:22 PST
References:   1 2 3
Followups:    1 2
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Oh joy! My first flame!!! (Terrell D. Drinkard) writes:

...lots of my own stuff deleted...

>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 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.

>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.

>A bit of corporate propaganda here, the first person to meet the BA 747
>(which landed in Manila, I believe) was the Boeing service engineering

Don't get me wrong I like Boeing aircraft, and I am fairly sure that the 747 is 
the only plane that could have survived this problem.

>No, those two incidents could not have been covered by ETOPS because ETOPS
>is concerned with Extended range Twin engine OPerationS.  ETOPS will not
>protect you from volcanic ash (there is an industry wide effort to track
>and report volcanic ash clounds, but their results have not been published
>yet, as far as I know).  It will protect you from bad maintenance, however.

I know what ETOPS stands for!  As yet there has not been a case where an ETOPS
aircraft has gone down, so I have had to take examples from other operations
to illustrate the dangers.  

>Also, I fail to see how the absolute number of engines mounted on the
>airframe would have prevented those scenarios.  The 747 carries 4.  Only

Once again, nothing could have prevented them, but the extra backup of 4 or 3
engines allowed them to survive.

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

Oh just that ash got into places that were never imagined, so that the plane
was never again as reliable as comparable aircaft in the fleet.  

>>Sorry about the rambling.  I just think twin engined aircraft are a bad

>Yes, I gathered that.

>>and while I consider them acceptable for short/medium haul routes,
>>I think that Long over water ones are just an accident waiting to happen.

>Over the entire history of turbine powered airliners no twin engined
>aircraft has had a accident stemming from both engines shutting down for
>two unrelated reasons.  Ever.  I pray it never will happen, but I think
>many of the worst years are behind us.  Things only seem to be getting
>better, ie, more reliable.

>>The 777 gives me nightmares.  How many people do we have to kill before
>>the airlines stop this crazy quest.

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

>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.

>>  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.

>>  I have
>>also clocked up well over 500,000 miles in the air.  In that time I have
>>had one engine lost to a bird strike (Conway), two in flight precautionary

Got that wrong, it was JT4, not a conway.

>>shut down's (RB211's), and one aborted take off (RB211 again) due to engine
>>malfunction.  I don't know how atypical these numbers are, but the incidents
>>have been frequent enough for me to actively avoid the 767 on trans-atlantic
>>flights.  Now my statistics all end up being British engines, but that is 
>>because I usually fly B.A.  I am sure the American manufacturer's figures
>>will be equivalent.

>It is difficult to say how typical your experiences might be without some
>idea as to how many takeoffs and landings that putative 500,000 miles might
>encompass.  Industry data are typically generated by hours or by cycles
>(takeoff and landing being a single cycle).  But anecdotal data are no
>substitute for a serious study of the issues.

I can tell you exactly, 171 cycles.  Most of my flights have been London to
LAX/SFO so in general are very long flights.

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.  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.

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:

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 guess I had better say that these opinions are all mine.

-- Pete Coe
-- Rational
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