AO-2009-004 Britten Norman BN2A-Mk III Trislander, ZK-LOU loss of engine propeller assembly, near Claris, Great Barrier Island, 5 July 2009

Shortly after take-off at approximately 1305 on 5 July 2009, the right engine propeller assembly of ZK-LOU, a 3-engine Trislander, separated from the engine crankshaft and struck the side of the aeroplane. Nobody was seriously injured, but the aeroplane fuselage was extensively damaged and a passenger door was removed, leaving a large opening adjacent to some passengers.
Undetected corrosion of the propeller flange had led to extensive cracking and its eventual failure. Safety issues identified included the need for detailed checking of overseas component records to ensure their reported in-service hours were accurate and for periodic crack checking of propeller flanges for corrosion damage. A safety recommendation regarding component record-checking was made to the Director of Civil Aviation, and the Civil Aviation Authority issued a Continuing Airworthiness Notice regarding inspections of crankshaft flanges for corrosion.
(Note: this executive summary condenses content to highlight key points to the reader and does so in simple English with less technical precision than the remainder of the report to ensure its accessibility to a non-expert reader. Expert readers should refer to and rely on the body of the full report.)