What happened
On 23 October, the VH-HWY departed Darwin Airport at 1307. While the initial forecast indicated thunderstorms and low visibility, the weather conditions intensified more rapidly than could have been predicted before departure. During the flight, the pilot requested diversions to avoid weather, moving the aircraft 10 to 20 NM off track.
As the aircraft navigated these diversions, it entered an area of intense convective activity characterized by rapidly developing towering cumulus clouds and precipitating cells. The aircraft's flight path placed it in close proximity to strong up- and down-drafts. During this period, the aircraft likely experienced severe turbulence and potentially reduced visibility, which may have led to spatial disorientation.
Following these encounters, the aircraft entered a very high rate of descent from approximately 10,000 ft until it struck the terrain. Evidence from the wreckage, including the position of the wing components and the deformation of the fractured wing spars, indicates that the wings separated from the fuselage in-flight. This separation was likely caused by excessive wing loading exceeding the structural limits of the aircraft.
The investigation
The ATSB examined the aircraft's track data, satellite imagery, and radar to reconstruct the flight path. Investigators analyzed the deformation of the wing spars, noting an upward and rearward direction of the fractures. While the precise airspeed at the moment of failure could not be determined, the investigation focused on how the combination of airspeed, turbulence, and pilot control inputs contributed to the aerodynamic load.
Investigators also looked into the decision-making process regarding the flight path. They considered whether the pilots' attempts to return to the original track or re-divert south inadvertently placed the aircraft in more hazardous weather. The investigation also explored potential motivational factors, such as the pressure to maintain a schedule or the pilots' relative inexperience in their roles, though no definitive link to these factors could be established.
Findings
- The aircraft encountered severe convective turbulence and precipitating cells that caused the wings to exceed their design load limits.
- The combination of airspeed, turbulence, and control inputs likely led to the structural failure of the wings.
- The pilots lacked sufficient operational experience flying in the Darwin region during the wet season, which is a period known for hazardous weather such as windshear and turbulence.
- The risk mitigation strategy of pairing a supervisory pilot with a new pilot was ineffective because neither pilot possessed the necessary experience for the specific seasonal weather conditions encountered.