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ASN Wikibase Occurrence # 248768
Last updated: 14 January 2022
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Type:Silhouette image of generic R44 model; specific model in this crash may look slightly different
Robinson R44 Raven II
Registration: ZS-RDI
MSN: 2393
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Location:Cypherkuil Private Farm -   South Africa
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Departure airport:De Poort private farm near Colesberg
Destination airport:De Poort private farm near Colesberg
Investigating agency: CAA SouthAfrica
Two occupants on-board a Robinson R44 helicopter with registration ZS-RDI took off from De Poort private farm near Colesberg, routing to Cypherkuil private farm, with the intention to land back at De Poort private farm. The flight was conducted under Visual Flight Rules (VFR) by day and in Visual Meteorological Conditions (VMC). The pilot reported that he was flying at low altitude, below 500 feet above ground level (AGL), while tracking game (springbok) on Cypherkuil farm when the helicopter lost tail rotor effectiveness (LTE) during a right turn. The helicopter started to spin in a clockwise direction. In an attempt to recover, the pilot pulled too much power and lost control of the helicopter. The helicopter landed hard on the ground with the skids first. The main rotor blades severed the tail boom and the helicopter rolled to the left before coming to a stop. The helicopter was substantially damaged during the landing sequence and the two occupants on-board were unharmed.
It is likely that during a right turn, with the helicopter flying at a low altitude, its airspeed decayed which resulted in the pilot abruptly increasing engine power to increase the helicopterís airspeed. However, the increase in power required by the main rotor exceeded the increase in power available or produced by the engine, causing the main rotor rpm to decrease if collective pitch is increased excessively. Because the tail rotor revolutions per minute (rpm) is tied to the main rotor rpm, the tail rotor speed also decreased. Although the engine was still providing maximum torque to the main rotor, the tail rotor was unable to provide adequate counter-torque as the thrust was greatly reduced due to the low rpm; this caused the loss of tail rotor effectiveness. As a result, the helicopter started to spin and the pilot lost control of the helicopter and crashed.

Probable Cause and/or Contributory Factors
Loss of control due to loss of tail rotor effectiveness induced by the low main rotor rpm. The low main rotor rpm was caused by an abrupt increase in engine power following a reduction in the helicopterís airspeed.

Contributory factor:
Improper recovery technique.
Low-level flight resulting in insufficient height to recover.



Accident investigation:
Investigating agency: CAA SouthAfrica
Status: Investigation completed
Duration: 7 months
Download report: Final report

Revision history:

13-Mar-2021 19:26 harro Added
13-Mar-2021 19:35 harro Updated [Cn, Category]
07-May-2021 12:05 harro Updated [[Cn, Category]]

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