Following a number of accidents and serious incidents involving Robinson R22 helicopters where a failure of either one or both rotor drive v-belts has led to the occurrence event, the Australian Transport Safety Bureau (ATSB) initiated a Safety Issues investigation into the broader question of Robinson R22 v-belt operational reliability.
What the ATSB found
There were no systemic safety issues identified as a result of the ATSB investigation. However, drive belt reliability was found to be negatively influenced by a broad range of operational and maintenance-related factors, including:
- high gross or overweight operations
- high or excessive engine power settings (manifold pressures)
- sheave misalignment and/or poor drive system condition
- inadequate or infrequent inspections of the rotor drive system.
What's been done as a result
In July 2011, the ATSB issued safety advisory notice AO-2011-060-SAN-001, reinforcing the need for continued vigilance by operators and maintenance organisations regarding the routine inspection of the R22 drive system.
During the course of this investigation, the Robinson Helicopter Company released an updated ‘Revision-Z’ v-belt. Since that change, R22 industry feedback has indicated an overall improvement in the stability of the drive system and a reduction in failure rates.
The Robinson R22 helicopter is the most popular light utility helicopter used in Australia and has a reputation for being an extremely reliable machine. Owners and operators should fully appreciate the nature and effects of the operational stresses placed on the helicopter, particularly if the machine is utilised in a dynamic and demanding manner such as required for cattle mustering operations.
Pilots, operators and maintainers should pay particular attention to the installation and condition of R22 drive belts and other components of the drive system, and should ensure that the manufacturer’s requirements for inspection and maintenance of the drive system are adhered to at all times.
The continued safe flight of an R22 helicopter that has sustained a v-belt failure can be assisted by the pilot’s awareness of the indications of a drive system malfunction, and the appropriate management of the emergency autorotation in accordance with published procedures.
In response to a fatal Robinson R22 helicopter accident and a number of other occurrences involving failure of Robinson R22 helicopter V-belts, the ATSB has commenced a safety issues investigation regarding the reliability of the Robinson Helicopter Co. model R22 drive belt system.
Since the commencement of this investigation, the ATSB has examined accidents, incidents and occurrences involving Robinson R22 drive belt (V-belt) failures. Stemming from that, no significant safety issues have been identified to date in the manufacture or design of the drive belts that might present an airworthiness issue for continued safe operation of the Robinson R22 helicopter fleet.
Industry feedback indicates that failures have been relatively infrequent since Robinson introduced the 'Revision-Z' drive belt standard. Once the initial break-in period is complete, the final stability of the belt system is reported to be much better than has been the case with earlier revision belts. The 'Revision-Y' belts were prone to stretch that required periodic adjustment of the drive system throughout the life of the belts.
Although no singular issue has been identified with the drive belt construction, it should be recognised that the belts represent a critical link in the main rotor drive system. Belt failures are often rapid and may be preceded by the onset of vibration or the smell of burning rubber. The ATSB reinforces the need for continued vigilance by operators and maintenance organisations during the routine inspection of the R22 drive system. Some of the factors that can influence the reliability of the R22 drive system are:
Regular inspection: It is an Australian regulatory requirement that the daily inspection of the drive belts and sheaves must be performed by a licensed aircraft maintenance engineer, a pilot endorsed on the aircraft type or an approved person, in accordance with the R22 Aircraft Flight Manual. The ATSB advises that particular vigilance should be applied during these inspections as they represent a fundamental opportunity to detect the onset of deterioration of the drive system. Any form of drive belt damage such as blistering, cracking and tie band (webbing) separation indicates that the belts require replacement.
Robinson Service Bulletin SB-66 highlights the importance of inspecting the sheaves. If the wear pattern is noticeably different from groove to groove, it is recommended that the drive belts be immediately replaced. The surface condition of the sheaves should be smooth and uniform.
Another prime inspection opportunity exists prior to installation of the belts. Careful inspection of the drive belts at this time may identify any surface abnormalities.
Operation: Pilots must monitor Manifold Air Pressure (MAP) to avoid exceeding the placarded power limits, as listed in the Robinson R22 flight manual. Exceeding the drive system limitations may result in sudden belt failure. Refer to Robinson Safety Notice SN-37.
Environment: Operating the helicopter in environments where dust and grit can contaminate the drive system, or where the ambient temperature is high, can also influence the service life of the belts and sheaves. Helicopters operated in these environments may require additional periodic inspections of the drive system.
Sheave alignment: Correct sheave alignment after installation of the drive belts is critical in ensuring the belt longevity.
High gross weight operation: Pilots must ensure that the approved gross weight limits are not exceeded while operating the helicopter.
Clutch actuator: The electrically-driven clutch actuator automatically controls drive belt tension. A cockpit caution light will illuminate when the actuator is re-tensioning, engaging or disengaging the belts. Robinson Safety Notice SN-33 suggests that a problem with the drive belts may be imminent if during flight the clutch light flickers or stays on for longer than normal. Under these circumstances the pilot is advised to land immediately.
ATSB Safety Advisory Notice AO-2011-060-SAN-001
On 6 July 2011, a fatal Robinson R22 accident (AO-2011-060) occurred near Julia Creek, Queensland. The ATSB found that the helicopter sustained an in-flight failure of the drive belts and in the interests of transport safety, issued a Safety Advisory Notice that urged pilots, operators and maintainers to pay particular vigilance to the R22 helicopter drive belt system.
This information is released in accordance with subsection 25(2) of Part 4 of the Transport Safety Investigation Act 2003.
|Date:||14 July 2009||Investigation status:||Completed|
|Investigation level:||Systemic - click for an explanation of investigation levels|
|Location:||ATSB Central Office Canberra|
|State:||Other||Occurrence type:||Propeller/rotor malfunction|
|Release date:||30 April 2013||Occurrence category:||Other|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Robinson Helicopter|