Accident Britten-Norman BN-2A Trislander Mk.III-1 ZK-LOU, Sunday 5 July 2009
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Date:Sunday 5 July 2009
Type:Silhouette image of generic TRIS model; specific model in this crash may look slightly different    
Britten-Norman BN-2A Trislander Mk.III-1
Owner/operator:Great Barrier Airlines (New Zealand)
Registration: ZK-LOU
MSN: 322
Year of manufacture:1972
Engine model:Lycoming O-540-E4C5
Fatalities:Fatalities: 0 / Occupants: 11
Other fatalities:0
Aircraft damage: Substantial, written off
Location:near Great Barrier Island Airport (GBZ) -   New Zealand
Phase: Initial climb
Nature:Passenger - Scheduled
Departure airport:Great Barrier Island Airport (GBZ/NZGB)
Destination airport:Auckland International Airport (AKL/NZAA)
Investigating agency: TAIC
Confidence Rating: Accident investigation report completed and information captured
A Britten-Norman BN-2A Trislander Mk.III-1 passenger plane sustained substantial damage in an accident near Great Barrier Island Airport (GBZ), New Zealand. There were ten passengers and one pilot on board. Three passengers suffered minor injuries.
At about 13:00 the 3-engined Trislander took off from Great Barrier Aerodrome at Claris on Great Barrier Island on a regular service to Auckland International Airport (AKL).
When climbing through about 500 feet the pilot heard an unusual "pattering" sound. He also heard the propellers going out of synchronisation, so he attempted to resynchronise them with the propeller controls. He checked the engine's gauges and noticed that the right engine manifold pressure and engine rotation speed had dropped, so he adjusted the engine and propeller controls to increase engine power. At that time there was a loud bang and he heard a passenger scream. Looking back to his right the pilot saw that the entire propeller assembly for the right engine was missing and that there was a lot of oil spray around the engine cowling.
The pilot turned the airplane left and completed the engine failure and shutdown checks. He transmitted a distress call on the local area frequency and asked the other company pilot, who was airborne behind him, to alert the local company office that he was returning to Claris.
Despite the failure, ZK-LOU continued to climb, so the pilot said he levelled at about 800 feet and reduced power on the 2 serviceable engines, completed a left turn and crossed over the aerodrome and positioned right downwind for runway 28. There was quite a strong headwind for the landing, so the pilot elected to do a flapless landing and keep the power and speed up a little because of the possibility of some wind shear.
After landing, the pilot stopped the airplane on the runway and checked on the passengers before taxiing to the apron. Three of the passengers received some minor abrasions and scrapes from shattered Perspex and broken interior lining when the propeller struck the side of the fuselage.

1. 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.
2. 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.
3. 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.
4. The crankshaft was an older design that has since been progressively superseded by those with flanges less prone to cracking.
5. 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.
6. 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.
7. 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.

Accident investigation:
Investigating agency: TAIC
Report number: 09-004
Status: Investigation completed
Duration: 8 months
Download report: Final report



photo (c) TAIC NZ; Great Barrier Island Airport (GBZ/NZGB); July 2009

photo (c) TAIC NZ; Great Barrier Island Airport (GBZ/NZGB); July 2009

photo (c) via Werner Fischdick; Auckland International Airport (AKL/NZAA); January 2007

Revision history:


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