Manufacturer's Guidelines for the Overhaul of Aircraft Propellers
The Propeller Manufacturer provides guidelines for the overhaul of aircraft propellers by calendar months, or in-flight hours whichever occurs first. While Part 91 aircraft are advised to complete an overhaul, Part 135 aircraft are required to overhaul their propellers.
Harzell propellers (built before 1997) have a recommemended TBO (time between overhaul) of 5 years or 2,000 flight hours. TBOs for all Hartzell Propellers can be found in Hartzell Service Letter 61Y at the following: Hartzell Propeller Inc. Service Letter
McCauley's TBOs are listed at the following: McCauley's Service Bulletin SB137AE
Sensenich released the following bulletin regarding the recommended overhaul of its metal propellers: Sensenich Propeller Service Bulletin No. R-17
Overview of an Aircraft Propeller Overhaul
The propeller is visually inspected to determine if the propeller qualifies for an overhaul. Obvious reasons that a propeller would NOT qualify for an overhaul would include ground strikes or severe corrosion. (On occasion we may suggest that you invest the small fee to have your propeller visually inspected to determine if your propeller will likely make overhaul for trade or resale purposes) If the propeller passes a visual inspection, the propeller will be disassembled and the parts will be cleaned as pictured in the photo to the left.
As prescribed by the overhaul manual for each specific propeller, blades and various other reusable components are measured. As pictured in the photo to the right, the width, the thickness and the length of the blades are measured at specific stations or distances from the butt of the blade. Measurements are taken on other components as well. The blade measurements and other measurement inspections become part of the work order folder.
The finish is stripped off the aluminum and steel components - generally through sandblasting. The aluminum parts are then etched with a caustic solution and inspected by magnetic particle, eddy current and using an ultraviolet light or dye penetrant system as illustrated in the photo to the right.
The propeller will then be reassembled in accordance with the overhaul manual and set to the specified torque values and blade angle settings. The overhaul manual for each manufacturer has an established list of parts that must be replaced at each overhaul that includes seals and o-rings, mounting studs and nuts, blade ball and needle bearings and all hardware. All specifics regarding the replacement of parts become a permanent part of the work order folder. Of course A.D. notes, Service Bulletins and Service Letters are checked and complied with as required.
Finally, propellers are lubricated and the prop is statically balanced (see photo to the left). Once the propeller is mounted on the aircraft, a dynamic balance should be performed. For information on the importance of dynamically balancing your propeller see our webpage on dynamic balancing.