What happened
On the morning of 29 January 2005, a Cessna 172 performing a specialized aerial survey for the New Zealand Police struck terrain in the Doolans Creek Valley, approximately 7 km south of Gibbston. The aircraft, registered ZK-LLB, was engaged in a low-level operation to identify illicit cannabis plantations.
After departing Queenstown Aerodrome, the aircraft was observed by witnesses flying at a low altitude in a slow, circling pattern over the Kawerau Valley. During the mission, the aircraft descended into a confined mountainous area. While the pilot had briefly reduced altitude to a level that diminished maneuvering margins, a subsequent, more rapid descent occurred, resulting in the aircraft striking the side of the valley in controlled flight. The impact destroyed the aircraft and caused the two fatal injuries of the pilot and the police observer.
The investigation
Investigators examined the aircraft's maintenance history and flight performance. Although the engine had undergone repairs for a stuck exhaust valve earlier that week, inspections of the wreckage showed no evidence of mechanical failure or engine power loss. The aircraft had sufficient fuel remaining at the time of the crash, making fuel exhaustion unlikely.
Analysis of the flight path revealed that the aircraft was circling in a mountainous region where the valley walls narrowed significantly at the site of the impact. The investigation looked into whether the pilot's view was obstructed; it was noted that the aircraft's configuration and the bank angle during the final turn may have masked the approaching terrain from the pilot's perspective. The investigation also considered the operational requirements of the survey, which necessitated low-level flight that inherently reduced safety margins in rugged terrain.
Findings
- The aircraft was operating in a controlled flight state at the time of impact.
- The pilot had descended to an altitude that did not provide enough space to safely maneuver around the valley sides.
- A sudden, further descent occurred, the cause of which remains undetermined, though engine failure was ruled out.
- The pilot's view of the approaching terrain was likely obscured by the aircraft's nose and instrument panel during the final turn.
- The terrain feature (a terrace) caused the valley to narrow more sharply than expected at the level the aircraft had descended to.