All Robinson R22 helicopters.
This Continuing Airworthiness Notice (CAN) is issued to draw attention to the occurrence of main rotor drive failures on R22 helicopters and the inspection/maintenance requirements of main rotor drive systems. This CAN provides a guide to the information available with emphasis on the inspection and maintenance requirements of main drive belts.
This CAN is prompted by numerous reports of R22 main rotor drive system failures in New Zealand and Australia. Investigation revealed a significant number of main drive belt failures may be due to either maintenance and/or the type of aircraft operations. Failures include low TIS main rotor drive belts. R22 aircraft on aerial work operations are subject to more strenuous operations which may have a detrimental effect on main rotor drive system reliability.
Typical Main Drive System Failures:
Several reported failures of newly installed main drive belts were described as feeling "sticky", "soft" and "stretchy" at the time of installation. In one instance a set of drive belts had a lumpy drive face which caused excessive vibration. Experience has shown that drive belts are more likely to fail due to the belts not having been inspected for defects prior to installation, and newly installed belts are more likely to fail due to not adhering to the correct V-belt ‘break in’ procedure.
Failures are due to pre-existing defects in drive belts not being identified prior to installation, incorrect tension of new/used belts, the unacceptable surface condition of the sheave V-grooves, incompatible sheave types used as a pair, sheaves installed in the incorrect position, misaligned sheaves and incorrect actuator rigging.
Some failures of the lower pulley bearing have been due to incorrect servicing of the lower pulley bearing.
Reports of cracks found in the lower pulley bracket have been attributed to excessive vibration from the engine cooling fan and lower pulley or sheave.
In addition, an in-flight alternator drive belt failure may interfere with the operation of the main rotor drive belts and can result in malfunction or failure of the main rotor drive belts.
Recommendation:
The CAA strongly recommends operators/maintainers of R22 aircraft consider the following:
Applicable References:
Manufacturer information which pertains to the maintenance of the R22 Main Rotor Drive System :
Manufacturer information which pertains to the operation of the R22 helicopter :
Note: The above mentioned references are for general guidance and may not be revised in this CAN. These references are not intended to exclude any other approved data or new information including ADs.
All other enquires regarding this CAN should be made to:
Owen Olls
Airworthiness Specialist
Email: ollso@caa.govt.nz
Phone: 04 560 9569
