|
Proper Propeller Maintenance Recently Transport Canada made changes to the Canadian Aviation Regulations Airworthiness Manual Standard 625 Appendix C (4) Out of Phase Task and Equipment Maintenance - Variable Pitch Propellers extending the Calendar Time Between Overhaul (TBO) to 10 years. Additionally, the Exemption to CAR 605.86(1) that extended the interval for internal inspection from 5 to 6 years has also been cancelled. These two changes were justified though an amendment to CAR Standard 625 Appendix B Part 1 (8) Scheduled Inspection for Small Aircraft other than Balloons - Propeller Group by marginally improving the annual external inspection requirements. These changes are being viewed as a relaxation to the previous standard that may compromise air safety. As the premier propeller repair shop in Canada, Western Propeller has serviced most types and models of propellers operating under all conditions and maintenance schedules. As robust as these vital components are, it is surprising how even small, seemingly insignificant defects will render them unserviceable or will potentially cause a catastrophic failure. Propellers are one of the most highly stressed (and often most neglected) components of the aircraft. Even under the best of operating circumstances the propeller is subjected to incredible amounts of stress, which include:
Yet even under these operating extremes, the propeller is expected to continue to function trouble free. To ensure this trouble free operation, periodic and regular maintenance is mandatory. The performance of the annual external inspection is easy; do a visual inspection of the blades looking for any signs of cracks, nicks and pits. Check the hub and blade roots for any signs of grease or oil leakage, then if any defects are observed, perform the appropriate repair. However, this external inspection is superficial and it leaves cracks, pits and corrosion on interior surfaces undetected. These can only be found once the propeller has been disassembled and stripped.
Propeller Manufacturers are the experts on their individual propeller models and the specific applications. A considerable amount of engineering time is spent designing, testing and approving propellers and their applications. Likewise, through TBO development programs, overhaul periods and service life limits are also specified. The results of these programs are the published maximum Flight Hours and Calendar Months for the propeller TBO limits. The propeller manufacturers all have specifications that provide a recommended TBO period. Adherence to these specifications will ensure that the factory warranty is not compromised. However if the Manufacturers' schedules are not followed then, "the manufacturer will be relieved of all obligations and liability under the warranty." Additionally, insurance coverage issues must also be considered. It is the responsibility of each individual owner to ensure that the aircraft, and in this case, specifically the propeller is adequately and reasonably maintained. Adequate maintenance may be more than just meeting the legislated requirements for the time between overhauls and in some instances and under some conditions it should exceed even the limits as set out by the Manufacturer. The owner must decide, aided by the AME and the expertise of the propeller maintenance specialist, as to what constitutes adequate maintenance. In the interest of aviation safety, it is the recommendation of Western Propeller "that in all cases, the legislated propeller TBO requirement be surpassed and that at a minimum the specified Flight Hours and Calendar Months TBO of the specific propeller Manufacturer be followed." The following are the propeller Manufacturer's Time Between Overhaul (TBO) specifications:
For more information on proper propeller maintenance please contact one of our Locations and also visit the following Internet sites: AOPA Air Safety Foundation - Safety Advisor Propeller Safety Worldwide Aircraft Propeller Association (WAPA) Hartzell Propeller Inc., General Service and Maintenance McCauley Propeller Systems, Propeller System Technology Guide |
