Re: Power for Take-Off

Date:         08 Sep 97 02:03:42 
From:         Chris Dahler <dahler@iglobal.net>
Organization: gte.net
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> On a recent trip, as we began our take-off run, the fuel pump in the
> left engine on a B757 malfunctioned.  We were moving slowly, so
> stopping was a simple matter.  Thankfully, the worst problem was a 6
> hour delay for the next flight.  One of the flight attendants on the
> second flight recognized me from the aborted flight.  I asked about
> the engine problem, and she directed me to the pilot from the first
> flight.  I expressed concern about losing power in one engine at a
> more critical point (liftoff), but he assured me that a fully loaded
> B757 would still have enough power to leave the ground.  Was he just
> trying to soothe my fears, since the event already passed, or is the
> plane actually that powerful?

Jack:

All multiengine aircraft, from light piston twins to the B-747, have to
be able to accelerate to takeoff speed, lose an engine, and still be
able to meet certain climb criteria before the FAA will certify the
aircraft as airworthy.  This is what makes a two engine airplane such a
powerhouse when compared to a three or four engine aircraft (such as the
B-727 and the B-747).  The certification process only requires one
engine to be inoperative, so a B-727 is dealing with a loss of a third
of its power, and a B-747 is dealing with a loss of a fourth of its
power.  However, two-engine aircraft like the B-757 are dealing with a
loss of a full half of their power.  Therefore, the engines have to be
much bigger on a two-engine aircraft to accommodate the loss of one and
still be able to meet the engine-out climb criteria.

Chris Dahler
dahler@iglobal.net