What happened
On 28 March 2007, an Aerospatiale AS 350 B helicopter, registration ZS-RSW, was performing a domestic flight to transport three technicians from the Simmerpan Eskom Yard in Germiston. After picking up the passengers, the pilot attempted to take off from a grass area near several high-rise buildings.
During the transition from a hover to forward flight, the pilot performed a power check at approximately 25 feet above the ground. As the aircraft accelerated to a speed of 10-1s knots, a low rotor RPM warning sounded. In an effort to recover the rotor speed, the pilot lowered the collective pitch and descended toward a nearby road intersection. However, as the pilot attempted to climb away again, the low rotor RPM warning recurred.
The aircraft's right-hand skid struck the windscreen of a light delivery vehicle at the intersection, causing the helicopter to pitch nose-down and roll onto its left side. The main rotor blades subsequently struck a second vehicle. The collision resulted in one fatality—the driver of the second vehicle—while one passenger in the helicopter sustained minor injuries and others escaped unharmed.
The investigation
SACAA AIID investigators examined the aircraft's weight and balance records, engine components, and the takeoff site. The investigation included a teardown of the Turbomecham Ariel 1 B engine. While the engine was found to be capable of delivering design power, investigators noted that the fuel control unit's temperature compensator adjuster cover lacked a manufacturer's seal, suggesting prior adjustment.
Investigators also evaluated the takeoff environment, noting the presence of high-rise buildings near the takeoff area and the lack of proper aeronautical aids, such as a functional windsock, at the unapproved landing site.
Findings
- The helicopter exceeded its maximum allowable takeoff weight, weighing 1999 kg against a maximum of 1950 kg.
- The excessive weight directly impacted the engine's ability to maintain sufficient power and rotor RPM during the transition to forward flight.
- The takeoff area was constrained by high-rise buildings, which likely created uneven wind patterns contributing to the decay in rotor RPM.
- The takeoff site was not an approved helipad and lacked a proper windsock or a designated safe escape route for emergency maneuvers.