What happened
On the afternoon of Monday, 4 June 2001, a Bell UH-1H Iroquois helicopter, registered ZK-HJH, was performing an approach to Taumarunui when a catastrophic failure occurred. Witnesses observed the aircraft enter a turn before plummeting toward the earth. During the descent, the helicopter was seen to break apart in mid-air. The impact resulted in 3 fatalities.
The investigation
While an initial investigation had been conducted, the inquiry was later resumed to incorporate significant new evidence emerging from two other unrelated UH-1 helicopter accidents. This reopened analysis focused on re-evaluating the mechanical failures that led to the loss of the aircraft. Investigators performed extensive metallurgical testing and component examinations to determine the precise sequence of events.
Crucially, the resumed investigation was able to rule out a previous theory suggesting that the tail rotor crosshead had become loose due to improper maintenance. Instead, the physical evidence pointed toward a different mechanical failure within the tail rotor assembly.
Findings
Technical examinations established that a tail rotor blade pitch link had been bent at some point during the flight. This deformation led to the development of cracks, which eventually resulted in a fatigue failure of the link. The failure of this component caused the pilot to lose control of the aircraft, leading to the in-flight breakup and subsequent crash. While the investigation confirmed the link failed due to bending fatigue, the specific cause of the initial bending remained undetermined.
Safety action
Following the identification of risks regarding the airworthiness and operation of ex-military aircraft, the Civil Aviation Authority initiated safety actions. Additionally, specific safety recommendations were issued to the Director of Civil Aviation to address the identified concerns.