What happened
On the morning of 10 August 2005, a Cessna U206G, registration ZK-WWH, departed Queenstown Aerodrome bound for Mount Cook Aerodrome. The aircraft was carrying a pilot and five passengers. Shortly after the aircraft became airborne, the pilot encountered severe control difficulties. The aircraft began to yaw and roll violently to the right, followed by a roll to the left, causing the left wing tip to strike the runway. The aircraft failed to remain airborne and eventually came to rest on its nose in the grass. While the aircraft sustained substantial damage to the engine compartment, propeller, landing gear, and left wing, there were no injuries among the occupants.
The investigation
The investigation examined the aircraft's condition, the environmental factors, and the loading configuration. Although the pilot had performed cleaning procedures to remove frost from the leading edges and control surfaces, investigators found that a layer of frost remained on the upper surfaces of the wings. The investigation also looked into the possibility of wake turbulence from a preceding Cessna 206, which had taken off just before ZK-WWH. Additionally, the investigation reviewed the aircraft's weight and balance, noting that the center of gravity was likely positioned aft of the rear limit for take-off. The loading of the aircraft included unsecured skis in the cabin and ski boots in the baggage area.
Findings
- The primary cause of the loss of control was the presence of frost on the upper wing surfaces, which degraded aerodynamic performance.
- The aircraft's center of gravity was likely behind the allowable rear limit during take-off.
- While wake turbulence from a preceding aircraft may have contributed to the initial upset, the frost was the main factor.
- Baggage and cargo, including skis, were not properly secured within the cabin or baggage area.
Safety action
Following the investigation, several safety issues were identified, including the necessity of ensuring all critical flight surfaces are entirely free of contaminants like frost before departure. There was also a noted need for improved pilot awareness regarding wake turbulence encounters and the requirement for more precise weight and balance calculations that account for all relevant conditions. Furthermore, the investigation highlighted the importance of accurate passenger safety briefings and the proper restraint of all cargo and baggage.