Synopsis
On 10 February 1999, a Heyns Helicopters Mi-8 MTV-1 helicopter (registration ZS-RIP) was involved in an accident while attempting to deliver a cooling system to the top of a building in Cape Town. The helicopter crashed on the roof of Boston House, resulting in the deaths of all four occupants. The accident occurred at 0420Z under fine meteorological conditions.
Accident Sequence
The previous day, strong winds prevented the planned lift, so the operation was rescheduled for the following morning. Two sections of the cooling system were positioned at the Grand Parade. At 0400Z, the helicopter departed from the Newlands Forest Heli-port and flew to the Grand Parade, where it hovered while the load was attached to the cargo sling.
The helicopter then lifted and proceeded westward along Strand Street, which had been closed to traffic. As it approached Boston House, the helicopter turned 90° to the right and positioned itself above the building. It then turned another 90° right, now facing east. While hovering, the tail rotor came very close to a "Stannic" advertising board on an adjacent building. Shortly thereafter, the tail rotor contacted the advertising board. After about two seconds, the helicopter began spinning anti-clockwise. The tail boom swung through approximately 180°, the helicopter lost altitude, and the tail boom struck a building wall, breaking off at its attachment to the fuselage. The helicopter plummeted nose-first onto the roof of Boston House, bursting into flames upon impact. Minor explosions were heard shortly after.
Probable Cause
The South African Civil Aviation Authority determined the probable cause to be: During the final positioning phase of the flight, as the helicopter was manoeuvred in a clockwise direction, insufficient tail rotor clearance was maintained, causing the anti-torque tail rotor blades to make contact with an advertising board. This resulted in a complete loss of control. The helicopter yawed anti-clockwise and pitched forward into the building, crashing on the roof of Boston House, fatally injuring the crew.