Re: A 777 with four engines.

Date:         06 Jul 98 03:24:40 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
References:   1 2 3
Followups:    1 2
Next article
View raw article
  or MIME structure

>The BAe 146 is a small plane. Planes that size don't need four engines
>but it has them for extra safety and to bypass ETOPS restrictions.

Since the BAe-146 has a still air range of only 1,300 miles (according
to AW&ST's Source Book), ETOPS isn't much of an issue.  That's why you
don't generally find more than two engines on regional aircraft.  From
what I've heard, the 146 has four engines simply because when it was
built, four of the ALF502 engines were more efficient and closer to the
thrust requirements for the plane than two of anything else available.
Neither safety nor ETOPS had anything to do with it.

>Why does the A340 exist when the A330 is the same size and has only
>two engines? To exploit the greater freedoms in the rules which planes
>with more than two engines enjoy.

While Airbus has sold a fair number of A340s on the basis of avoiding
ETOPS restrictions, the main reason for building both was to provide
greater range -- the basic A340-300 has over 60% greater range than the
same-sized A330-300.  When the A330/340 were designed, engines large
enough to build a twin with the range of the A340 didn't exist and thus
the A340 was born.  Now that such engines exist and Boeing has built the
777 around them, Airbus has of course made a virtue out of not needing
to follow ETOPS rules, while at the same time producing a long-range
twin in the form of the A330-200.

--
Karl Swartz	|Home	kls@chicago.com
		|Work	kls@netapp.com
		|WWW	http://www.chicago.com/~kls/
"The average dog is a nicer person than the average person." - Andrew A. Rooney