Recommendation Date
Recipient Name
ATD MoT
Text
Consider if a requirement exists for a fence/guard to be developed by the manufacturer, e.g. similar to that used to protect the elevators on the Pilatus Porter.
Reply Text
The installation of a protective fence/guard is not considered feasible or necessary. The Fletcher aileron utilises a shielded horn balance configuration and the gap between the horn and the wing when the aileron is deflected is integral to this type of design and does not lend itself easily to any form of guard. The Pilatus Porter has an unshielded horn balance, so this problem does not arise to the same extent.
There is a modification to Fletcher FU24-950 ailerons which fits endplates to the aileron horn balance and these provide some protection against the ingress of vegetation and deflecting it away from the area. This modification, AI/FU/0137 is available for retrofit under Service Bulletin 052; it is fitted as standard to all Crescos and since 1980 to all new production FU24-950s.
However, the primary purpose of the modification is to improve the roll rate and decrease stick forces and it is not known what the effect of the increased roll rate would have been if the modification had been fitted to the accident aircraft.
The level of protection is not such as to justify making the modification mandatory by the issue of an Airworthiness Directive. Nor is it considered that the development of any other protection is justified, as this could involve a significant redesign of the lateral control system.
There is a modification to Fletcher FU24-950 ailerons which fits endplates to the aileron horn balance and these provide some protection against the ingress of vegetation and deflecting it away from the area. This modification, AI/FU/0137 is available for retrofit under Service Bulletin 052; it is fitted as standard to all Crescos and since 1980 to all new production FU24-950s.
However, the primary purpose of the modification is to improve the roll rate and decrease stick forces and it is not known what the effect of the increased roll rate would have been if the modification had been fitted to the accident aircraft.
The level of protection is not such as to justify making the modification mandatory by the issue of an Airworthiness Directive. Nor is it considered that the development of any other protection is justified, as this could involve a significant redesign of the lateral control system.
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