What aircraft was involved and where did it happen?

The accident on 2000-07-01 involved a aircraft, at NZ.

What was the probable cause of the accident?

The accident was caused by an excessive tailwind during final approach, which was compounded by the pilot's incorrect assessment of wind conditions and inadequate performance data in the aircraft flight manual for the specific runway slope and wind parameters.

Tailwind causes aircraft overrun at Great Mercury Island

A Piper PA 32-260 charter flight overran an uphill grass runway at Great Mercury Island, resulting in substantial aircraft damage but no injuries.

What happened

On 1 July 2000, a Great Barrier Airlines charter flight carrying four passengers was landing at Great Mercury Island when the Piper PA 32-260, registration ZK-DSQ, overran the uphill grass runway. The aircraft touched down approximately 90 meters past the runway threshold. Despite the pilot's attempts to brake on the wet surface, the aircraft could not be stopped before reaching the top of the slope. The plane continued downhill past the end of the airstrip, colliding with a boundary fence and striking a post, which caused substantial damage to the wing and fuselage. There were no injuries to the occupants.

The investigation

Investigators examined the pilot's approach and the environmental conditions at the time of the accident. The investigation established that while the pilot had the necessary training and licenses, he lacked significant experience operating at this specific airstrip. The pilot had relied on a windsock observation from the downwind leg to estimate the wind, which led to an incorrect assessment of the tailwind component. Furthermore, the investigation looked into the reliability of the automatic weather station at the site, noting that its wind direction reports may have been inaccurate and required calibration.

Findings

Several factors contributed to the accident:

The primary cause was an excessive tailwind encountered during the final approach.
The pilot's decision to land was based on an inaccurate estimation of the wind component, likely due to observing windsocks from a distance rather than a direct overhead survey.
The airline's operations manual used a tailwind component limit that was difficult to calculate accurately from reported wind directions.
The aircraft flight manual's performance charts did not provide sufficient data for the specific slope and tailwind conditions present at the Great Mercury Island airstrip.
The wet grass surface reduced braking effectiveness, exacerbating the overrun.

Safety action

Following the inquiry, several recommendations were made to improve safety:

The airline was advised to amend its operations manual to use simple wind speed and direction limits rather than complex tailwind components.
Instructions were issued to extend aircraft flight manual performance data to cover the specific requirements of the operations being conducted.
The operator was advised to ensure the automatic weather station at Great Mercury Island was properly calibrated and reported wind relative to magnetic north.