Re: DC-9 Flight Control/ hydraulic systems

From: (Robert Dorsett)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         22 Jun 96 18:30:40 
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In article <airliners.1996.972@ohare.Chicago.COM> kls@ohare.Chicago.COM (Karl Swartz) writes:
>>>In the case of AAL 191, the sole changes to be implemented ...
>>Wasn't something done along the lines of having a mechanical downlock
>>installed to physically keep the slats in position with only positive
>>hydraulic pressure able to "lift" them?
>Discussed, but never added to the DC-10.  American also requested and
>was willing to pay for a modification kit to move the hydraulics from
>the leading edge of the wing to a safer location, but MD refused to
>produce it.  (The 747 and L-1011 had both mechanical slat locks and
>safer routing of the wing hydraulics from the very beginning.)

And in any case, the important thing to remember is that it was just a few
knots which meant the difference between safe flight and stalling out.  The
failure mode only became significant because the emergency engine-out
procedures did not take into account the possibility of inadvertent slat
retraction, which, compounded by the lack of warning mechanisms, reflected
poorly on both the FAA regulatory requirements and how Douglas chose to
implement them.

So, if airlines are faced with the option of a multi-million-dollar hardware
upgrade, or simply resetting reference speeds to be a few knots faster and
accepting takeoff penalties, they're going to go with the latter.

Robert Dorsett                         Moderator, sci.aeronautics.simulation