Re: SURGE ON GE90 ENGINE

From:         drakeal@aol.com (Drakeal)
Organization: America Online, Inc. (1-800-827-6364)
Date:         06 Jun 95 10:11:05 
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>I read in Aviation Week that one of the GE90's on BA's first 777 had
>experienced a "surge".  Can anyone tell us what a surge is and why it's of
>concern?  Will this problem delay the delivery of the BA aircraft?


A surge is the same as an engine stall.  Basically, it is when the local
pressure ratio across a compressor stage is too high, and the air stops
flowing forward and rushes back out the front of the engine.  The result
is often a loud bang, accompanied by flames flaring briefly at the engine
inlet.  Very  spectacular and upsetting to passengers.  Stalls occur for
various reasons, from damage to the compressor to incorrect fuel flow
settings.  Most modern jet engines (the GE90 included) incorporate
variable geometry stator vanes; these contribute to compressor stability
by regulating the amount of air admitted to the compressor.  When these do
not move to the right angle at the right time, stalls can result.
Scuttlebutt says that this incident was due to FOD, or Foreign Object
Damage.  I interpret this to mean that a piece of hardware came loose in
the engine and damaged the compressor.

Stalls are important in this case, because the GE90 program is trying to
gain its ETOPS or Extended Twin Engine OperationS, certificate from the
FAA and CAA.  The ETOPS certificate enables an aircraft to be up to 180
minutes from any airfield at any point in its flight, in the event of an
engine failure.   This allows an aircraft to fly more efficient
transoceanic routes that are farther from possible divert airfields.  To
do this, it has to show a certain level of reliability.  The GE90 is
behind the Pratt & Whitney 4084 in getting its ETOPS.  This incident could
put it even further behind.  BA's contract with GE may be contingent on
recieving ETOPS certification by a particular date.  They may refuse to
accept the aircraft until the ETOPS is granted.  The ETOPS war is key in
the struggle between GE, P&W, and Rolls Royce; whoever gets flying quicker
will recieve the bulk of initial orders for their engines.  To companies
who have sunk enormous amounts of capital into the development of these
powerplants, that could be crucial.