Slat extension locks

From:         rdd@cactus.org (Robert Dorsett)
Date:         29 Jun 93 09:22:55 PDT
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In previous DC-10 discussions (last year, mainly), I erroneously referred
to the Boeing use of "jackscrews" to lock leading edge devices.  This is
incorrect.  Jackscrews are used to some extent for trailing edge extension,
but aren't used for leading edge devices in any airplanes I'm familiar with.

I recently learned that the locking mechanism for the LED's is to trap 
hydraulic fluid downstream of the actuator.  The locking mechanism is located 
in the extension piston itself, and may not be opened again except by more 
hydraulic pressure, during the retract cycle.  

Thus, if the hydraulic system is lost, the device itself will remain firmly 
wedged extended, with a small quantity of hydraulic fluid present in the 
sealed piston.  Probably held more firmly than with hydraulic pressure 
present.  

I'm told that this system is so reliable that it's caused many a problem for 
maintenance-type people once an actuator itself fails: there's no way to 
retract the slats on the ground.  Boeing apparently sells a little hand-
pump to permit the fluid to be removed, but I'm told of one incident which 
involved the use of a hacksaw. :-)

Sorry for any confusion, for those who hang on my every word. :-)


Egomaniacally,

---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd