What was found
(CAN) ON 24 FEBRUARY 2015, WITH 3 CREW MEMBERS ONBOARD WAS PRACTICING WATER LANDINGS. ON TAKEOFF THE CREW NOTE A HIGH NP 1214 RPM, NORMAL 1200 RPM. THE ACFT RETURNED TO BASE & MX TECHNICIANS FOUND THE SPRING STRUT ASSEMBLY BROKEN. THIS SPRING STRUT LINKS THE ENG INPUT QUADRANT TO THE FUEL CONTROL & PROPELLER CONTROL UNITS. IT COMPENSATES FOR ENG TORQUE WHEN POWER IS APPLIED OR REDUCED. IT WAS DISCOVERED THAT THE SHAFT PN 87620130-101 HAD SHEARED IN THE THREADS AT THE LEVEL OF THE FORK END PN 87620129-101. AMPHIBIOUS ACFT TECH SUPPORT WAS CONTACTED TO REPORT THE INCIDENT. A RESEARCH WAS DONE ON THE INTERNET & ON THE ADVISORY CIRCULAR 43-16A ALERT 336, DATED JULY 2006 ON 21 APRIL, 2002 A REGISTERED DASH 8 ACFT HAD A SIMILAR INCIDENT. CA060424008 SHAFT BROKEN 4/21/2006, DHC8301 PW123 87620130101 PROPELLER FLIGHT CREW REPORTED EXCESS BACKLASH & PROP SYNC DOES NOT SYNC. PROP WANDERING + - 5 TO 7 RPM. ENG SPRING STRUT ASSEMBLY REPLACED. AFTER DISASSEMBLY IN THE OH SHOP, SHAFT PN 87620130-101 WAS FOUND BROKEN AT POINT RIVET PN MS204170AD3. THE SIZE OF THE RIVET HOLE LEAVES MINIMAL MATERIAL AROUND THE SHAFT, WHICH IS PRONE TO BREAKING UNDER VIBRATION.