5th of July 2009
A Britten-Norman BN-2A Trislander MK.III-1was scheduled to operate a passenger flight between Great Barrier Island Airport and Auckland International Airport, both in New Zealand, on this day in 2009. Onboard a pilot and 10 passengers.
The aircraft after landing, note the missing propellor, damaged fuselage, and the missing passenger door (Source & © TAIC)
The weather was good but windy. Clouds were scattered at ~2500 feet, with some showers in the area and a 15 to 20-knot wind down runway 28 with good visibility. After all preparations were completed the engines were started, and will all indications normal the aircraft taxied to Runway 28. The pilot lined up the aircraft after receiving his take-off clearance applied full brakes and applied full power on all three engines. A check of all engine instruments showed everything was indicating normal the brakes were released at 13.00 lt (local time) and the aircraft started its take-off run. The take-off was without incident up to 500 feet, at that altitude the pilot heard an abnormal, engine, sound. And it appeared that the propellors were no longer synchronised. Using the propellor controls he attempted to synchronise the propellers. He also observed the manifold pressure and the engine speed for the right engine had both dropped. He, therefore, adjusted the engine and propellor controls to increase engine power. While adjusting the controls a loud bang was heard, followed by screams from the passenger compartment. While looking toward the right engine he observed that the propellor was missing from the engine, with oil streaming over the engine cowling.
The damaged interior (Source & © TAIC)
The applicable engine failure and shut down checklists were completed, and a distress call was made on the local area frequency. On the two remaining engines, the aircraft was continuing to climb and was leveled off at ~800 feet. Power was reduced on the two remaining engines and a left turn was initiated to start crossing over the Great Barrier Island Airport to position the aircraft for a right downwind back to Runway 28. As there was a strong headwind, the pilot elected to perform a flapless landing, keeping the airspeed up because of the change of some windshear. After an uneventful landing, the pilot stopped the aircraft on the runway to assess the situation of the passengers, before continuing to the apron. Three of the passengers received minor injuries as a result of a broken Perspex aircraft window and broken interior lining.
The two parts of the failed crankshaft, the left part remained on the propellor, the right part remained on the crankshaft (Source & © TAIC)
Damage to the aircraft was extensive;
Fractured crankshaft, that caused to propellor to fall from the aircraft
Fuselage was damaged
Aircraft window shattered
The passenger door fell off the aircraft after the hinges were damaged by the propellor.
The aircraft interior pushed inwards, into the cabin
The Transport Accident Investigation Commission (TAIC) of New Zealand investigated the incident and in their report (available by clicking on the field below).
They identified the following findings that caused or contributed to the incident;
The engine propeller assembly separated from the right engine of ZK-LOU in flight and struck the fuselage when the crankshaft failed at the flange that connected it to the propeller hub.
High-cycle fatigue cracking on the flange that had developed during normal operations from undetected corrosion had reached a critical stage and allowed the flange to fail in overload.
The crankshaft had inadvertently passed its overhaul service life by around 11% when the failure occurred, but the company had not realised this because of an anomaly in the recorded overseas service hours prior to importation of the engine to New Zealand. Ordinarily, the crankshaft would have been retired before a failure was likely.
The crankshaft was an older design that has since been progressively superseded by those with flanges less prone to cracking.
There was no requirement for a specific periodic crack check of the older-design crankshaft flanges, but this has been addressed by the CAA issuing a Continuing Airworthiness Notice on the issue.
The CAA audit of the company had examined whether its engine overhaul periods were correct, but the audit could not have been expected to discover the anomaly in the overseas-recorded engine hours.
This failure highlighted the need by potential purchasers of overseas components to follow the guidelines outlined in CAA Advisory Circular 00-1 to scrutinise overseas component records to ensure that the reported in-service hours are accurate.