On 9/7/2010 11:10 AM, Eric Munk wrote:
Going on some years of experience maintaining three high-time Puchaczes,
I'd say these are your options:
- Rudder not properly installed after maintenance. The only thing holding
the rudder in place is a castelled nut (visible from the underside of the
fuselage, behind the tailwheel). To remove the rudder for maintenance,
remove the split pin and castelled nut, and the rudder may be lifted off
upwards. The rudder cables are attached to a rudder drive - butterfly
shaped - that automatically connects when the rudder is refitted. Lovely
system, actually. Now, sometimes people do not take out the lower
(castelled) nut, but the nyloc nut that holds the bottom rudder hinge pin
to the rudder itself. That saves some time fiddling with splitpins (while
working upside down), but also creates the hazard of rehanging the rudder
without fitting this nut, and to a quick inspection from the underside of
the aircraft it looks OK (bottom castelled nut properly fitted), while it
is actually loose in the aircraft (top nyloc missing). I had one of these
when I did an annual after maintenance, lovely situation to catch in
time...
- Service Bulletin BE-058 not complied with, not checked or improperly
done. It says to check the bottom nut. If another type of nut is there
(e.g. nyloc), it needs to be replaced by a castelled nut. Shortly
afterwards, a Puchacz in the UK lost its rudder: it had a nyloc replaced
by a castelled nut, but the inspector in question had overlooked that a
hole for the splitplin was already there when he drilled a new one,
weakening the bolt which subsequently failed. All other SB's relating to
the rudder system, were regarding the attachment of the cables to the
rudder pedals (which were a completely different although very important
problem altogether).
- A structural problem. There's two known weakpoints in the Puch's
rudder attachment. First (a minor one) is the plywood (vertical) support
under the rudder cable drive (the butterfly shaped thing). The glued joint
on the topside (to the horizontal plywood mount of the butterfly lever)
tends to fail sometimes. However, this alone should not result in the
rudder to depart the aircraft, or even the rudder controls to become
difficult. Then there's also the problem the GFA alerted the world about
(but which has not yet made it into an SB or AD) of cracks found in the
horizontal support plywood of the butterfly lever. This however, should
result in the rudder becoming inoperable, but it should remain on the
aircraft since the mounting is not affected. Then there's always the
chance of a different hitherto unknown structural problem altogether...

Just giving you information to work out the problem at hand. Not pointing
fingers here (which is a pointless thing to do anyway).

Eric

I don't normally like to repeat an entire post, but (and speaking as someone
who has never actually seen a Puchacz in the flesh) this one deserves it IMHO.

Thanks, Eric, for an informed, informative and hugely useful post in response
to a (we can hope!) isolated if bizarre incident that could fairly easily have
ended badly. If I ever buy (or see) a Pooch, I know one area where I'll be
peering more intently, now!

Regards,
Bob W.