PPRuNe Forums - View Single Post - Jackscrew End Stop Probably Cause of AS 261 Crash
Old 8th December 2002 | 20:13
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Belgique
 
Joined: Mar 2000
Posts: 301
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From: Obvious
THE NASA FAILSAFE JACKSCREW

The solution to the Alaska 261 jackscrew failure problem is the recent NASA invention of the FAILSAFE JACKSCREW. It was cunningly designed by NASA to overcome a single critical failure Shuttle-Launch catastrophe problem (failure of disconnects and pull-backs prior to lift-off). NASA also identified it as a solution to the type of failure that downed Alaska 261. There are photos, drawings and descriptions at the following links.


link ONE

link TWO

link THREE

link FOUR (NASA's failsafe jackscrew pdf file)

link FIVE

link SIX

link SEVEN

link EIGHT

link NINE

link TEN Air Safety Week Magazine's Article on the FS Jackscrew

link ELEVEN Earlier Air Safety Week Article on the FailSafe Jackscrew (pdf file of 654kb)


Unfortunately the FAA (Transport Airplane Directorate) has already dismissed the Failsafe Jackscrew as being "out of the question" due to the Alaska 261 crash being caused solely by human failure (i.e. maintenance error inasmuch as a worn but not yet threadbare screw was not replaced two years before the crash and this failure to mantain being exacerbated by caked grease also preventing the screw-threads from being lubricated). The FAA's own Cost-benefit analysis does not justify the cost of replacing existing jackscrews with this NASA Failsafe Design.

The Story of why that failing AK261 jackscrew was NOT replaced is in large part the story of Whistleblower John Liotine (links 7 & 8).

On 10 Dec 02 the NTSB will possibly follow the lead of ex-member Dr Loeb when he condemned the 737 rudder design as having
insufficient "reliable redundancy". When McDD had the MD-80/90 jackscrew design certified originally it was upon the false premise that the horizontal stabilizer was "structure" and therefore did NOT come under that part of FAR25 that lays down strict redundancy and single-point failure rules for flight-controls. It is now patently obvious that the horizontal stabilizer and its jackscrew are indeed critical "flight controls"
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