All CA21, CA22, CA22A, CA22/25, CA22N, CA2S & CA25N aircraft with wing TIS greater than 300 hr. or older than 12 months.

An aileron hanger rib trailing edge extension was broken with very little downward pressure during a non-scheduled inspection. This Service Bulletin is an immediate response to this incident and a future bulletin will require additional drainholes and internal inspections in some aircraft. The aircraft on which the rib was discovered was 2.5 years old and was stored outdoors in a slightly nose down position which could have reduced the effectiveness of the wing drainholes. The rib appeared in good condition except for shallow depressions and the paint was intact.

The requirements of this Service Bulletin are mandatory and are to be carded out before next flight with the exception of a flight to an approved maintenance organisation after a suitable preliminary inspection by the pilot.

A good indication of possible deterioration is fabric wrinkles or a hole and movement in the areas shown. All hanger ribs to be inspected as follows:

• Check each hanger rib trailing edge extension by squeezing the sides gently with multi- grips or prodding with a narrow flatbladed screwdriver. Compare the hardness of different areas. Remove the turtledeck to facilitate inspection of the inboard side of the butt hanger rib.
• Grasp each hanger rib extension individually from the top, placing the thumb on the top edge and push down firmly testing the structural integrity. There should be no movement between the trailing edge and the extension.
• Using a similar grip continue testing the structural integrity by twisting the extensions firmly in both directions.
• Look for depressions where plywood fibres have collapsed causing a sucked in appearance.
• Any indication of deterioration should be further investigated as follows:
• Remove paint in the suspect area shown using a knife or chisel dragged at surface 75-85° to the surface.
• if all the paint is removed easily in 2 or 3 scrapes, dry rot is present. If some paint can be lifted off including wood fibres attached to the back of the paint, dry rot has affected the plywood. Refinish the scraped area if no damage is found with Epiglass Evidure epoxy wood preservative and paint.
• Contact Skyfox Aviation for repair advice if any doubt exists regarding serviceability before further flight.

Peter N Moller

Production/Airworthiness Manager 27/2/98