Re: DC-10 Modifications after ORD

From:         Jim Innes <>
Organization: Canada Internet Direct, Inc.
Date:         21 Oct 96 13:31:40 
References:   1
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Mark Ingram wrote:
>On 12 Oct 1996, Jim Messina wrote:
>> I read the long NTSB report posted here two months ago about the AA DC-10
>> crash at O'Hare years ago. I am still uncertain what modifications were
>> done to the DC-10 fleet as a result. Can someone summarize them. Thanks

>Years ago I asked almost the same question of a former MD engineer who
>taught my DC-10 systems ground school.  I don't remember everything
>he  said, but he did say that one of the main changes was in how the
>leading edge devices are "locked" into position.
>I put quotes around the word locked, above, because unlike most (all?)
>Boeing jets, which indeed use a mechanical locking mechanism which
>cannot be unlocked in the absence of hydraulic pressure, the DC-10 has
>always used *hydraulic* locking of LED's.
>In the American accident, a rupture of the main hydraulic lines to the
>LED's in the left wing caused the devices to retract.  So, the design was
>modified such that the LED's were truly locked after extension, right?

The design was actually modified after a overrun incident in MIA.
The system is actually "hydraulic balance relief valves", they are located
as close as possible to the outboard slat drive actuators, and well outboard
of the engine attachment area around the pylon.

> According to my source, no:  The *hydraulic* locking was only moved
>closer to the actuating cylinders.  The LED's (according to my instructor)
>could still suffer an unwanted retraction under certain circumstances.

A second change after MIA, was to modify the cable system controlling tthe
two hydraulic vavles which control the outboard slats. This mod will
prevent slat retraction even if the command cable is damaged.

>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).

The feeling about Souix City amongts some of us is that the real problem
was never fixed, the powerplant. The CF6-6D has had a terrible history of
uncontained failures. The close proximity of hydraulic systems is a
problem on alot of aircraft designs, anybody remember JAL in Osaka?

Just some thoughts,
Regards Jim Innes