Skyfox CA25N, VH-PSM, on 1 May 1999

As the Skyfox Gazelle climbed to approximately 250 ft above ground level following take-off, engine power reduced significantly, and engine vibration increased. The pilot landed the aircraft on the runway distance remaining. 

An investigation carried out by the aircraft's maintenance organisation revealed no defect that could have led to the loss of power. Two days later, the aircraft experienced similar engine problems, and the pilot conducted another precautionary landing. This was followed by a third similar incident 3 days after the second event. In both of those subsequent incidents, investigation revealed no defect that could have led to the loss of power.

Although the reason for the engine power losses could not be determined, it was found during the investigation that the air intake system on the aircraft incorporated two lengths of wire reinforced impregnated cloth hose, commonly known as "SCAT" hose to transfer air from the air intake box underneath the engine, via the rear of the engine, to the two carburettors on the top of the engine. SCAT hose was approved by the Civil Aviation Safety Authority as a part of the intake system for the Rotax 912 engine on the Skyfox aircraft. 

The Civil Aviation Safety Authority has subsequently issued advice on SCAT hoses in an information leaflet entitled "SCAT/SCEET Hoses". The leaflet stated, in part, that "SCAT and SCEET hoses manufactured by Thermoid RHD industries and marketed as Aeroduct flexible ducts, are not approved by the manufacturer for use as a piston-engine intake duct/hose. Contrary to popular belief, Aeroduct "SCAT" and "SCEET" hoses, as detailed in certain aviation parts supplies catalogs, are not approved by the hose manufacturer for use in negative pressure applications. 

This effectively prevents the use of Aeroduct SCAT and SCEET hoses as engine intake hoses." A negative pressure application is one in which the air pressure outside the hose is greater than the air pressure inside the hose. In an engine intake application, air is drawn through the hose by the engine past an air filter. In this case, the air pressure outside the hose is greater than the air pressure inside the hose. The hose is not designed to withstand such a pressure difference, and it is possible that the hose could collapse, causing an obstruction to the airflow to the engine. Investigation revealed no indication that the SCAT hose had collapsed during the occurrence.