Re: DC-10 Modifications after ORD

From:         Mark Ingram <markt@mickey.mo-net.com>
Date:         12 Oct 96 21:34:29 
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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

Jim,

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?

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.

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).

We *both* thought that the result of such a complete hydraulic failure
would be a deep, $100-million hole in the ground, and in this regard -
fortunately for Al Haines and his crew and passengers - we were wrong.

Mark E. Ingram

MarkT@Mo-Net.Com (also mingram@mail.orion.org)