Hi! Fred
Whilst I don't purport to be an authority I must contribute as follows:-
As frustrating as you may find it, the Mod 73 identifies a positive
eventuality of the centre bush becoming unbonded and allowing the
stabilators to migrate outwards and so disengage from the drive pins at the
close out rib end. Indeed only a small number were found to have become
unbonded but unless mod 73 is effected then you will never be sure, nuisance
though it is.
I understand that the main failure found on G-OFHC was a delamination of
the final lay ups on the WING close out rib (due to insufficient scuffing
preparation (on a photo I saw) and not least by the nearby aft wing lift pin
pulling out of the threaded stack of aluminium/layup sandwiches in the rib
close out , the aluminium plates having individually moved during curing
resulting in the drilled hole prior to threading missing full engagement of
the plates.
More recent kits have wider plates allowing for more error of centralization
of the hole, the original kits only used 1" wide plates allowing for minimal
error but the kit instructions did warn of the potential for the plates to
move during working and curing.
It was not the flap pin which failed but indeed the flap drive pin just may
have become disengaged by the flap moving outboard.
Whichever came first to precipitate the sequence of events is somewhat
immaterial, both mods to wing and stabilators are in best interest but also
serious checks of the degree of engagement of the flap drive pin into the
flap drive tube when the flaps are deployed should be followed as per Europa
Technical Bulletin.
Regards
Bob Harrison G-PTAG
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Fred Klein
Sent: 14 October 2009 07:13
Subject: Europa-List: Mod 73
With the premise that the only stupid questions are those which aren't
asked, I have a couple for anyone who'd like to comment on this Mod 73.
As I recall, Mod 73 is a direct outcome of the initial concerns
following William Mills' tragic in-flight break up...particularly a
concern that the triggering event was one of the tailplanes moving
outboard and decoupling from the pins on the torque tube flange.
Following the grounding of UK-based Europas, Mod 73 was devised,
approved, and implemented on the entire UK fleet as well as on many
other aircraft based elsewhere. From the list prepared of those who
implimented Mod 73 (I don't believe) any instances were discovered or
reported of incipient failures.
Subsequently, the accident investigation (if I recall correctly)
determined that the triggering event was a failure caused by the
incorrect location of embedded aluminum plates on the inboard face of
a flap...a condition which precluded the proper threading for the flap
pin which was pulled free and destabilised the aircraft...a condition
totally unrelated to issues intended to be addressed by Mod 73.
If I am even partially incorrect thus far, please enlighten me.
So my questions are:
- Is Mod 73 a required mod for any aircraft based outside of the
UK?...particularly in the US?
- If not, why implement Mod 73 when there is no evidence that a
problem with the original design exists?
- Is Mod 73 an example of a prematurely arrived at "fix", approved and
implemented in a rush to get the Europa fleet airborne again before
the real culprit was determined...and...does it remain in effect today
out of a reluctance of regulatory agencies to set things right?
Thanks for any comments and input,
Fred
A194
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