22. PERIODIC REPLACEMENT OF SAFETY CRITICAL PARTS SAFETY CRITICAL PARTS Nr. No. Replacement interval 1 Every 2 years or 4000 hours, which ever comes sooner 2 Every 2 years or 4000 hours. 3 a b PC450-ENG c 3-19 . Safety critical parts for periodic replacement Q’ty Fuel hose (fuel tank - engine) 1 Return fuel hose (engine - fuel tank) 1 Front pump hoses (line filter - control valve) 2