I recently had a landing accident in N44EU which was
precipitated by power failure during a go around; N44EU, a Mark
1, incurred "substantial damage" (FAA assessment). I was
fortunate to walk away with minor bruises and scratches.
In analyzing the accident later, I concluded from all the
details of the power failure that the most likely cause was that
the throttle cables kinked within the throttle block when I
attempted to rapidly apply full throttle, effectively locking the
power at the existing setting.
With the throttle at idle, several inches of cable are within the
throttle lever block and are not constrained by the sheath. When
the throttle is advanced, the springs at the carburetors normally
take up slack in the cable. Should the throttle lever be
advanced faster than the springs take up the slack, the cable can
loop downwards and kink within the throttle lever block,
effectively locking the throttle at a setting providing much less
than commanded power.
I expect that the rate at which the springs can take up the slack
will vary between aircraft depending on the routing of the
throttle cables, cable lubrication, and any other friction or
mass in the throttle cable system. In my case, I used powdered
graphite lubricant on all cables rather than oil (this to avoid
dirt attracted by oil) - I doubt that this contributed to the
problem, but each builder must make a choice of lubricant for
himself. The awkward part is that dirt, temperature, and other
unknown conditions could affect the maximum rate of throttle
application before kinking will occur and this could vary between
flights. Further, rapid throttle application tends to occur when
power is needed rapidly so a pilot could exceed the critical rate
inadvertently.
A further consideration with this throttle system design is that
should one of the throttle springs break then a similar kinking
failure will almost certainly occur.
My understanding of the reason the spring is incorporated by
Rotax is to cause the engine to go to full power should a
separation occur within the throttle linkage, the concept being
that having full power is better than having less.
My inquiries turned up another report of a Europa which kinked a
throttle cable on takeoff resulting in less than full power and
an aborted takeoff with no serious consequences. This lends at
least a bit of credibility to my amateur accident investigation.
I don't know whether the XS model uses the same throttle design
so this may not apply there.
Until the cause is officially established, I believe Europa
builders who have throttles of the above described design should
use some care when advancing the throttle rapidly.
John Newtown, CT
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