Re: DC-9 Flight Control

Organization: MindSpring Enterprises, Inc.
Date:         23 May 96 10:37:33 
References:   1
Followups:    1 2
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  or MIME structure (billie durso) wrote:

>I am new to this subscription so please bear with me.  I was wondering
>about the recent crash of the Valujet DC-9, and arrived at the
>following question.  This question applies to all of the elder
>transports 727, 737, DC-9, DC-10...

>    I am pretty sure that all of these earlier aircraft had mechanical
>linkages to all of the primary flight control surfaces.  I also am
>pretty sure that these mechanical linkages were hydraulically boosted
>to easy in control of the aircraft.  Assuming a total power failure in
>the aircraft, are these hydraulic boosters shutdown?  If so the flight
>surfaces would become excessively hard to control.  If anyone out there
>has any experience with the design of these aircraft please give me an
>answer about this.  Could a fire in the main fusebox cause a total
>power fialure throughout th e aircraft.?  Let me know.  Thanks


The DC-9 series will fly fine without electrical or hydraulic power
The ailerons are a cable and tab system as well as the elevators
The rudder is normally powered by a hydraulic pack but automatically
reverts to a tab system with the loss of hydraulic pressure. The
horizontal stabilizer is electric and cannot be used without the main
busses powered. The landing gear can be lowered through a cable
system. The speed brakes are hydraulic and are also used to augment
roll control so roll won't be as effective but control wouldn't be a
problem. I have never heard of a DC-9 losing all hydraulic power since
each engine has it's own pump in addition to an electrically powered
aux. pump. The APU can also be run in flight and can supply electric
and pneumatic power. The apparent total loss of control of the
Valuejet aircraft hopefully will be discovered, but loss of systems
doesn't explain why it would just fall out of the sky.

P. Danclovic