Re: hydraulic failure

From:         geoffm@purplehaze.Corp.Sun.COM (Geoff Miller)
Organization: Sun Microsystems, Inc.
Date:         23 Mar 93 00:24:54 PST
References:   1
Followups:    1
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  or MIME structure (Joe Dellinger) writes:

>Now... a year after the event I'm sort of curious. Just how BAD
>a mechanical failure was that? It seems to me that not being able to turn
>the nose wheel at all and having to lower the landing gear by hand-crank
>is sort of NOT A GOOD SIGN.

It's no big deal, actually.  Large transport aircraft typically have 3-4
hydraulic systems, with the most levels of redundancy applying to the
primary flight controls (ailerons, elevators and rudder).  Other systems,
such as landing gear and flap extension/retraction, normal and emergency
wheel brakes and nosewheel steering, have fewer levels of hydraulic backup 
and are spread out among the separate hydraulic systems.  

Nosewheel steering is among the less critical systems employing hydraulic 
pressure -- perhaps the *least* critical --  so it generally gets its 
actuation pressure from only one hydraulic system.  If the nosewheel steering 
fails, it's a simple matter to steer the airplane with the rudder, and center 
it on the runway before slowing to a speed at which rudder authority is lost.

As for cranking down the landing gear, that's a simple, straightforward
procedure, albeit an uncommon one.

>And why did we fly straight through such awful weather to get back to LA?  Why 
>didn't they go above it, or around it, or something? 

Difficult to say for sure without knowing the facts of that particular 
situation.  Returning to LAX via the most direct route might've been 
considered more important under the circumstances than sticking to the best
route for a smooth ride.  And maybe the turbulence was worse than anticipated.

>How often do such "minor hydraulic failures" occur? Are they fairly common? 

Not very.  I've probably flown hundreds of hours in commercial aircraft since
my first flight in 1960, and I've never experienced an inflight emergency.
Nor do I know anyone personally who has.

>This one didn't make either the LA or Honolulu papers. Is that typical?

Sure.  Inflight malfunctions such as this one are relatively rare, but they
do happen from time to time.  And since the passengers were never in any 
danger, the incident wasn't newsworthy.  Your plane probably could've made 
it all the way without further incident, but it's standard procedure (and 
common sense) to land as soon as possible when an inflight failure occurs, 
simply as a precaution.


Geoff Miller			+ + + + + + + +        Sun Microsystems
geoffm@purplehaze.Corp.Sun.COM	+ + + + + + + +     Menlo Park, California