Re: DC-10 Modifications after ORD

From: (Brian A. Reynolds)
Organization: Rockwell Avionics - Collins
Date:         21 Oct 96 13:31:39 
References:   1
Next article
View raw article
  or MIME structure

re Slat latch.

On the MD-11, the slats (like those of the DC-10) are controlled by
hydarulaic cylinders moving a drum, with cables going from the drum to
the individual slats.  The MD-11 fault isolation drawings shows a 'slat
extend latch' on the slat cable drum. locking the slats in the extended
position.  How this lock gets 'unlocked' however is not all that clear
and I don't have access to the actual maintenance manuals of Illustrated
Part Catalog.

>We also discussed the vulnerability of the three hydraulic systems, with
>no control-cable backup, including their common routing through the tail
>section.  This gentlemen as much as predicted the UAL accident at Souix
>City (which was to happen several years after our discussion).

Not sure what you mean or what you would propose as an alternative,  The
DC-10 like all large aircrft cannot move flight control surfaces without
hydraulics.  It makes little difference how the hydraulics are commanded,
no hydraulics no movement.  In the DC-10/MD-11, the hyrdaulics are
commanded either by cables connected to the primary flight controls, or
through commands from the autoflight system to the hyrdaulic actuators
(in which case to cables causes the controls in the flight deck to move).
The two are combined in such a manner that the cable (i.e. flight crew
input) can over ride the flight control computer.  So the statement of
'no control cable back-up' is a non sequitur as the control cables cannot,
and were never intended to couple the flight crew directly to the control
surfaces. Doesn't work in big airplanes from any manufacture.  Crews arems
are not big enough :)  If you want to aircraft which have directly driven
control surfaces, stick with older designs in smaller aircraft.

As for common routing through the tail section - how is one to command
the control surfaces located in the tail unless the hyrdaulics and
associated control cables are routed there?  The elevator for example,
has all three hydraulic systems moving actuators.  If either one or two
systems fails, the surfaces can be moved by the third.  If one fails in
a 'hardover' position, the others can either move the surfaces against it
or 'out vote' the failed surface by voting three surfaces agains the failed

The design at this level was not at fault.  It was the routing of the
hydraulic lines combined with the lack of 'hydraulic fuses' to control a
ruptured hyrdaulic system (which have been added by the way) which related
to the loss of hyrdaulic fluid through the ruptured lines.