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.
Hartzell usedpropellers (built before 1997) have a recommended TBO of 5 years or 2,000 flight hours. TBOs for all Hartzell Props can be found in Hartzell Service Letter 61Y at the link below:
The airplane propeller is visually inspected to determine if the propeller qualifies for an overhaul. Obvious reasons that an airplane propeller would NOT qualify for an overhaul would include ground strikes or severe corrosion. (On occasion a PropellerMan technician 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 airplane propeller passes a visual inspection, the propeller will be disassembled and the parts will be cleaned.(picture left)
As prescribed by the propeller overhaul manual for each specific prop, 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 propeller 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.
During a propeller overhaul, 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 airplane 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, the airplane propeller is lubricated and the prop is statically balanced (see photo to the left). Once the propeller is mounted on the aircraft and while the propeller is running, a dynamic balance should be performed (see photo to the right).