What happened
On 22 April 2017, a Bell 430 helicopter, registration ZS-VDM, was performing a private positioning flight from Grand Central Aerodrome to the Spartan Helistop in Kempton Park. The pilot, accompanied by a second pilot acting as a passenger to provide guidance, approached the helistop for the first time. After a successful initial inspection of the site, the pilot executed a landing into the prevailing wind.
Upon touchdown, the aircraft began to roll forward due to a slight downslope on the helistop surface. The pilot attempted to use the toe brakes, but they were ineffective in stopping the movement. In an instinctive effort to arrest the forward motion, the pilot applied aft cyclic input. This action caused the main rotor disk to tilt significantly, leading the blades to strike the left vertical stabilizer and subsequently sever the tail boom. The aircraft experienced violent shaking and a 90-degree rotation before the crew shut down the engines to prevent fire. No injuries were reported.
The investigation
SACAA AIID examined the sequence of events, which were corroborated by ground-based video footage. The investigation focused on the physical state of the Bell 430, the characteristics of the Spartan Helistop, and the pilot's control inputs. Investigators noted that while the pilot had extensive experience, this was her first landing at this specific location. The investigation also reviewed the official helistop directory provided by the regulatory authority to determine if critical surface information had been communicated to users.
Findings
- The primary cause of the accident was the application of excessive aft cyclic to stop the forward roll, which caused the main rotor blades to contact the tail boom.
- The helistop surface possessed a slope for water drainage that was not documented in the official SACAA helistop directory.
- The pilot did not utilize the parking brake or request the co-pilot to apply his side's toe brakes during the roll.
- The pilot was unaware of the specific aft cyclic limitations of the aircraft when the collective pitch is nearly fully lowered.
- The pilot did not attempt to transition back into a hover to reposition the aircraft once the forward movement began.
Safety action
- It is recommended that the pilot undergo dual flight retraining on the Bell 430 to address knowledge gaps regarding control inputs during ground operations.
- It is recommended that the Spartan Helistop directory be updated to include specific longitudinal and lateral slope information to ensure pilots are aware of potential drainage gradients.