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Propeller Maintenance: What to Know About TBO Limits

Date: September 26, 2019 Category: Blog Tags: , , , , ,
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At Hartzell Propeller, we manufacture aircraft propellers, but our top priority is safety. Like any mechanical device, propellers require periodic maintenance and inspection to ensure a long life and safe operation in flight. If left unchecked, even small issues with your propeller can turn into larger—and more expensive—problems. For this reason, we encourage pilots to comply with the published TBO (time between overhaul) limits for their propeller model.

To clear up some of the confusion surrounding overhauls for propellers, we’ve put together this guide on what to know about TBO intervals.

What is the published TBO for my propeller?

Every aircraft propeller manufacturer, including Hartzell Propeller, has a list of overhaul times for their props based on calendar time (months or years) and flight hours. At Hartzell, we publish overhaul times based on in depth evaluations and testing by our team of skilled engineers. If you have a Hartzell prop, refer to the most recent revision of Hartzell Service Letter HC-SL-61-61Y and use your propeller model number to locate the overhaul limits that apply to you.

It’s important to pay attention to the limits set forth by your propeller manufacturer so you know when you’re getting close to overhaul time. Following the overhaul limits will ensure that any issues developing within your propeller are discovered early, while they might still be repairable.

Are pilots required to follow the manufacturer’s published TBO?

Pilots operating under Federal Aviation Regulation Part 91 are not obligated by the FAA to comply with a manufacturer’s service document. But even though complying with overhaul times is not a legal requirement, there’s a reason why manufacturers like Hartzell Propeller set overhaul limits for their props. Neglecting your propeller by operating it beyond these limits may not be illegal, but it could lead to reduced reliability, propeller malfunction, expensive component replacement, and potentially unsafe operating conditions.

At Hartzell, we’ve been designing and manufacturing propellers for more than a century. While our propellers were designed for high reliability and a long service life, we recognize the age limitations of the components within a propeller. Following our published overhaul limits will protect your safety and maximize the cost-effective operation of your propeller investment for years to come.

Should I follow the calendar limit or flight hours?

The short answer is to this question is whichever occurs first. Many times, pilots know their propeller’s published TBO period based on flight hours, but ignore the calendar limit. This could be a major safety concern, especially for general aviation pilots who fly fewer than 100 hours per year.

For example, say the overhaul limit for a propeller is 2,000 flight hours or 60 months (5 years). If a pilot flies 100 hours per year, they would only have 500 flight hours on their propeller at the end of the five-year period. If they waited to reach 2,000 flight hours before sending their prop in for an overhaul, it would take twenty years! The fact is, even if an aircraft is stored in a heated hangar, the propeller is subject to degradation over time due to corrosion, internal seal aging, and the breakdown of internal lubricants. This type of age-related damage caused to the propeller and hub isn’t always visible externally; it is usually only detected during a complete propeller disassembly and overhaul.

As you can see, it’s well worth it to take care of your propeller by having it overhauled and inspected within the published TBO limits. Next week, we’ll talk about what to expect during the overhaul process and how to find the right service facility for your Hartzell propeller.

Do you have a question for the Hartzell Propeller technical team? Complete an online contact form, call 800-942-7767, or email

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