Accident Summary
On 3 February 2021, a Robinson Helicopter Company R44 Clipper II, registered VH-SXC, operated by GSL Group Pty Ltd on a passenger charter flight from Proserpine Airport to Whitehaven Beach, Queensland, was cruising at 1,500 ft between Long Island and Hamilton Island. The pilot detected a burning rubber smell and observed the clutch warning light flicker. A subsequent bang from behind the cabin coincided with the clutch warning light illuminating steadily. The pilot turned back toward Long Island, declared an emergency to Hamilton Island air traffic control, and executed a successful emergency landing on the western beach of Long Island. The pilot and two passengers were uninjured, and the helicopter sustained minimal damage.
ATSB Investigation
The Australian Transport Safety Bureau (ATSB) investigated the incident and found that of the four drive belts in the helicopter’s drive system, the forward two belts had dislodged and moved forward of the upper sheave, lodging against the sheave and clutch shaft. This caused damage to the belts and surrounding components. The remaining two belts shifted forward from their original positions and were not effectively engaged within the sheave grooves. Consequently, there was a complete loss of effective drive to the rotor system.
In consultation with Robinson Helicopter Company (RHC), investigators determined that a previous procedure of extending the clutch actuator to stretch new drive belts was no longer advised. This procedure, which had been performed on VH-SXC, involved extending the actuator with the engine stopped to hold the belts under tension for an unspecified time. RHC identified that if performed regularly, this practice could lead to overstretching and looseness in the drive belts during start-up, potentially allowing the belts to drop below the lower sheave grooves and misalign during belt tensioning.
The ATSB noted that repairs to the helicopter had been conducted per applicable manufacturer instructions, and the stability of sheave alignment indicated that misalignment was not a source of the failure. The belt-stretching procedure, current at the time, was used on each set of drive belts and for an additional five flight hours to address tight belts. However, RHC later recognized that engaging the clutch actuator to stretch belt sets contributed to excessive slack at start-up. The safety notice (SN-33) did not specify that the stretching was intended as a one-time application; in-service feedback showed operators performed it multiple times, and repeated use likely contributed to belt repositioning during operation.
Manufacturer's Response
RHC amended Pilot’s Operating Handbook Safety Notice SN-33 ‘Drive Belt Slack’, which covers pre-flight inspection requirements and rotor turning time after clutch engagement. The company removed the procedure of stretching new drive belts by extending the clutch actuator with the engine off. The maintenance organization involved raised awareness among engineers and advised customers and operators of the removal of the stretching procedure. They also reiterated the requirement for main rotor blades to turn within five seconds of clutch engagement and to seek maintenance support if this limit is not met.
Pilot Actions
The pilot followed fundamental emergency priorities: aviate, navigate, and communicate. After diagnosing a drive train problem, the pilot responded to increasing engine speed and decreasing rotor speed by following the Pilot’s Operating Handbook (POH) procedure and maintaining control. The pilot pulled the clutch circuit breaker after the clutch warning light illuminated steadily. The report notes that had the circuit breaker not been pulled, the remaining two belts might have tensioned and restored drive, but given the symptoms, the pilot’s actions were prudent. The pilot then returned toward Long Island, selected a suitable landing site, and communicated the situation to Hamilton Island control tower.