Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: 2, 3, 4 engines-- what's actually safer?
Date: 19 Mar 93 00:07:39 PST

In article <airliners.1993.241@ohare.Chicago.COM> rdd@cactus.org writes:
>>In particular, I'm interested if anyone can think of an incident in which a
>>trijet survived (for some value of survived; a semi-controlled crash
>>landing, such as the Sioux City crash, would qualify) where a twinjet would
>>have (presumably) not done so.

Hi Robert!  Sorry to piggyback on your message, but the original one is
gone from our system, and I just read something today that is highly
pertinent to the discussion.

Gordon Bethune, the incoming Renton Division VP&GM, just made a speech in
Singapore on ETOPS, and he made two interesting statements.

1)  The number of accidents involving twin-engine jets which occurred
because of both engines shutting down for unrelated reasons: Zero. None.

2)  The number of accidents involving airplanes with more than two engines
with two engines shut down for unrelated reasons.  Two, both involving four
engined airplanes on take off.

The guy who made these statements was the VP of Boeing Customer Services
and is therefore quite conservative.  :-)   I hope this answers the
original question.  I now return to our regularly scheduled newsfroup.


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

Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: 2 engines vs 4 engines planes
Date: 30 Oct 93 22:33:43 PDT

In article <airliners.1993.673@ohare.chicago.com>,
Dietmar Hanke <acm@SkyNet.GUN.de> wrote:

>I have recognized that more and more aircrafts used for transatlantic
>flights just have 2 engines, like the B-767, B-757, A300 ...
>What happens if one of the 2 engines of a B-767 fails somewhere over the
>atlantic? Which distance can this jet still fly by just using one engine.

This is a slightly more complex question that you might first guess.
Currently, the 767 (with all the appropriate engines and auxilliary
equipment and crew/maintenance training & certification) is certified to
fly 180 minutes away from the nearest "suitable" airport.  Distance is
velocity multiplied by time, and the 767 is certified to fly at MMO
(maximum operating mach number) on one engine.  Interestingly, it can
actually do that.  :-)  Some folks opt for the Maximum L/D speed which
is somewhat slower.  So, basically, find a speed you like, and multiply it
by three.  That would be your answer.

Now.  Not all operators are certified for 180 minute ETOPS (the above example).
Some are allowed 120 minutes, some 90, some only 75.  Some aren't allowed
to fly ETOPS at all under any circumstances.  :-)  (Typically this is an
economic decision made by the airline - not a reflection of relative
safety - because of the onerous bookkeeping requirements.)

>Is it possible to fly a B-747 when 2 of the 4 engines failed? Was it even
>possible when both engines on one wing woudn't work anymore?

Yes.  (I just happen to have a 747 configurator right beside me.)

>I allways prefer a flight on a B-747 when I have to get from Frankfurt to
>New York if there were also 2 engine jets on that route. Would you think
>the same way?

No.  :-)  I'd go with the 767 because of the nicer seating arrangements.
Or maybe an MD-11 so that I can check out the competition's stuff.
Unless I could afford one of those cool upper deck seats.  :-)

>Thanx for a response to my questions.

No charge.



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

Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: 2 engines vs 4 engines planes
Date: 01 Nov 93 14:05:08 PST

In article <airliners.1993.679@ohare.chicago.com>,
Pete Coe <ditka!sgiblab!uunet.UU.NET!ucsd!frosty.rational.com!pete> wrote:
>acm@SkyNet.GUN.de (Dietmar Hanke) writes:
>
>>Is it possible to fly a B-747 when 2 of the 4 engines failed? Was it even
>>possible when both engines on one wing woudn't work anymore?
>
>Hey! 747's have been known to fly with no engines.  There was that British
>Airways 747 that flew into a volcanic ash cloud, and for 30 minutes or so
>became the world's heaviest glider.
>
>That incident, and others (e.g. Eastern Tristar losing all engines due to
>incorrect maintenance), leads me to think that as far as engines go, two
>is never enough.  The statisticians can argue the point as long as they
>like, but the fact is that more has to be safer.

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.

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.

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
representative.

>  I doubt that the two
>above incidents would be covered by ETOPS regulations, because they
>were not a fault of the engines, or airframe design.  But in both
>cases, the flight crew only managed to save the day because they
>could get _some_ power from _all_ the engines (as opposed to all
>the power from one of the engines). If either had been a twin, we
>would have lost passengers to another 'unfortunate incident'.

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.

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
the An-225 has more (6).  Your understanding of the hydraulic systems is
somewhat less than desireable.  All current production engines windmill and
thereby produce standby hydraulic power.  The number of hydraulic pumps on
the airplane is driven by power requirements and fault-tree analysis, it is
not some fortunate accident that the 747 was able to generate enough
hydraulic power to maintain control until the flight crew could restart the
engines - it was designed that way.  It is a regulatory requirement to
design that way.

>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
since'?

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

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.

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.

>  Although I am myself a professional
>in the aviation industry, I consider myself to be well informed.

I would dispute that.

>  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
>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.

>Rant mode off.
>
>--
>
>-- Pete Coe
>-- Rational
>-- Object-Oriented Products


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

Newsgroups: sci.aeronautics.airliners
From: rdd@cactus.org (Robert Dorsett)
Subject: Re: 2 engines vs 4 engines planes
Date: 02 Nov 93 00:38:06 PST

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

Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: 2 engines vs 4 engines planes
Date: 06 Nov 93 00:24:37 PST

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."

Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: Lufthansa advertisements, A340
Date: 02 Feb 94 01:35:09 PST

In article <airliners.1994.893@ohare.chicago.com>,
Jay Vassos-Libove <libove@tom.alf.dec.com> wrote:
> [gobs deleted]
>
>(Technical question, to justify the posting... WHY did Airbus
>design a 4 engine plane in the days of large Twins??)

There are two reasons that I'm familiar with.  One, there were no engines
large enough at the time of the A340's launch.  Note the 777 launched later
and has a very aggressive engine development program in order to support
the first flight date.  The A330 has relatively large engines, but not big
enough to give the heavier A340 the range it needed.

The more politically correct (in Europe) answer is that the direct
operating costs are reduced with four engines because of weight savings
due to the dead weight bending moment relief of the outboard engines.
This is extremely difficult to quantify, particularly given the announced
level of wing commonality between the A330 and the A340.  Makes one wonder
which airplane is carrying the weight penalty of the other's engine
arrangement.


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

Newsgroups: sci.aeronautics.airliners
From: ehahn@fairlite.mitre.org (Ed Hahn)
Subject: Re: Lufthansa advertisements, A340
Date: 02 Feb 94 01:35:11 PST

In article <airliners.1994.893@ohare.Chicago.COM> libove@tom.alf.dec.com
(Jay Vassos-Libove) writes:

<stuff deleted>
   (Technical question, to justify the posting... WHY did Airbus
   design a 4 engine plane in the days of large Twins??)

--------
This is because, to the manufacters and airlines, certifying a twin
for Extended Range (ER) operations is a major hassle:

-- The aircraft must demonstrate a certain number of flight hours
without engine trouble before being considered for ER certification.
This is to prove both that the engine can take it AND that a single
engine (plus APU) would be sufficient to power the electrical,
pneumatic (packs), and hydraulic systems to DIVERT to an emrgency
field.  A four engined aircraft doesn't even have to divert to a field
and can continue on 3 engines to its original destination (in theory -
in practice, most captains would elect to land ASAP).

-- The individual airline must apply for ER certification to prove its
maintenance program is up to snuff.

-- Even with ER certification, according to FAA standards, you still
have to fly at all times no further than a specified number of minutes
from an emergency field (90, 120, or 180 minutes depending on the
carrier/aircraft).  If you want to operate in REAL remote areas (i.e. the
pacific, etc), you are out of luck.

The A340 has 4 CFM56 engines (same basic type certified for B737
and B757).  Thus (obviously) ER certification does not apply, and
because these engines are pretty good, fuel economy-wise, they aren't
sacrificing that much.

Conversely, the A330, which has the EXACT same fuselage and wing
(except for engine pylons) as the A340, because it is a twin:

-- requires new engines (i.e. GE90, PW4080, and RR Trent) and
the attendent engine certification,

-- ER certification, which the flying prototype has been demonstrating
flying from Paris to Singapore or some other huge stage length (aside:
would YOU want to fly for 20 hours a pop?)

-- New engine maintenance programs on the part of the airlines.  One
example: the RR Trent cannot be transported as an intact unit on the
back of a tractor trailer; the fan must be removed and broken into a
several components, which then must be reassembled before
installation.  This is because the fan diameter is too wide and/or
high for the US interstates (without Wide Load trailers).

Anyways, the difference in range/payload between the A330/A340 is
small enough that some carriers are willing to eat the operating differences.

BTW, the B777 will be delivered to United with an ER certificate, but
will be the first aircraft to be so certified at initial delivery...

Hope this helps,
Ed Hahn
--
////////   Ed Hahn | ehahn@mitre.org | (703) 883-5988   \\\\\\\\
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really.