What happened
On June 28, 1998, an AS-350 helicopter, registration PP-EOE, operated by the São Paulo Military Police, was performing a specialized flight demonstration known as the "Mac Guire" maneuver in Indaiatary, São Paulo. The maneuver involves transporting personnel externally via suspension ropes to simulate rescues in difficult terrain.
During the demonstration, two military personnel were being transported suspended by ropes on the exterior of the aircraft. While the helicopter was in flight, the suspension ropes collided with kite strings coated with "cerol" (a highly abrasive glass-embedded substance used on kite strings). The impact caused the ropes to sever instantly, resulting in the two fatalities of the personnel being transported. The helicopter remained undamaged, and the remaining crew members escaped without injury.
The investigation
The CENIPA investigation focused on the physical properties of the broken ropes and the operational procedures of the flight crew. Laboratory analysis conducted at the Aerospace Technical Center (CTA) utilized stereomicroscopy and scanning electron microscopy (SEM) on the rope fibers. The results confirmed that the fibers had been sliced by an abrasive cutting object. Furthermore, energy-dispersive X-ray (EDS) analysis detected chemical elements consistent with the glass composition found in commercial "cerol" kite strings.
The investigation also examined the crew's pre-flight briefing and situational awareness. It was determined that while the pilot was experienced and the aircraft was properly maintained, the specific danger posed by kite strings had not been adequately addressed in the mission briefing. Additionally, the investigation found that a previous similar accident in Brasília had not been effectively communicated to the crew, leading to a lack of awareness regarding the extreme danger of even minimal contact with such strings.
Findings
- Low situational awareness regarding the specific risks of performing the "Mac Guire" maneuver in areas where kite strings might be present.
- Deficient planning, as the pre-flight briefing failed to address the necessity of checking the area for obstacles such as wires, poles, or kites.
- Inadequate communication of safety information, as the unit had not properly disseminated information regarding a similar previous accident, which prevented the implementation of more stringent preventive measures.
- The primary cause of the rope failure was the contact with kite strings coated with "cerol".