What aircraft was involved and where did it happen?

The accident on 2006-11-27 involved a aircraft, at NZ.

What was the probable cause of the accident?

The engine failure was caused by the mechanical failure of an exhaust valve tappet head, which released metal debris into the oil system.

Engine Failure in Gippsland Airvan Over Cook Strait

A scheduled flight from Wellington to Kaikoura was interrupted by a partial engine failure caused by internal component damage, prompting an emergency return to land.

What happened

On 27 November 2006, a Gippsland Aeronautics GA8 Airvan, registered ZK-KLC, was conducting a scheduled air transport flight from Wellington to Kaikoura. Approximately eight minutes after departing Wellington, while crossing the Cook Strait, the pilot experienced a sudden engine misfire accompanied by fluctuating oil pressure.

Recognizing the irregularity, the pilot immediately initiated a return to Wellington. Although the engine continued to run, the oil pressure remained unstable. The pilot successfully landed the aircraft at Wellington without further incident. Upon inspection by engineers, the engine showed significant internal damage, including metal debris found in the oil suction screen and pressure filter.

The investigation

TAIC investigators conducted a thorough engine tear-down and laboratory examination of the components. The investigation focused on the source of the metal contamination and the condition of the engine's oil system.

Technicians discovered that the engine's oil suction screen was clogged with metal particles. Further analysis revealed that the engine had suffered substantial internal damage. The investigation also looked into the operator's maintenance program, specifically regarding oil change intervals, and the physical condition of the exhaust system, which showed signs of buckling and splitting.

Findings

The engine failure was triggered by the break-up of a tappet head, though the specific reason for this component failure could not be determined.
The pilot was qualified and fit for the flight, and the engine was operated within normal parameters prior to the failure.
While the aircraft was maintained according to the operator's specific program, that program did not fully align with all manufacturer requirements.
The investigation found that the extended oil change interval used by the operator was not a contributing factor to this specific failure, as no damage from poor lubrication was identified.

Safety action

Following the incident, several safety improvements were implemented:

The operator updated its route guide to mandate a minimum altitude of 3000 feet when crossing the Cook Strait on the direct route.
The maintenance manual was amended to require more frequent oil and filter changes, specifically every 50 hours, and a spectrographic oil analysis program was introduced.
The manufacturer, Gipps Aero, added a 50-hour inspection requirement for the oil system to its service manual.
The Commission recommended that the Director of Civil Aviation inspect single-engine air transport operators to ensure compliance with regulations regarding flights over water.