propeller inspection | Stockton Propeller

Replacing vs. Repairing Your Airplane Propeller

An airplane’s propeller is one of the most highly-stressed and most-overlooked components on any aircraft. During routine operation, 10 to 25 tons of centrifugal force is pulling the hub’s propeller blades. Also, the propeller blades are bending and flexing due to thrust and torque.

Engineers design propellers to be properly maintained and to perform normally under these loads. But when damage occurs due to corrosion, stone nicks, or worse, additional unintended stress is imposed. In that case, the margin of safety may not be adequate. Operating an aircraft needing a propeller replacement or propeller overhaul can be a dangerous risk.

Propellers may need a professional propeller shop’s special attention and capabilities for many reasons, such as scheduled overhaul limits, operating inspections, and major repairs. Not to mention – propeller replacements!

If you’re worried about your propellers or require a propeller governor repair or propeller overhaul, talk to the experts at Stockton Propeller. With decades of experience and free service area pick-up and delivery, we’re the propeller experts who keep you flying!

A Quick Recap On Composite Airplane Propellers

Airplane propellers have been around, well, since the first powered flight. In the early days of aviation, propellers broke at an alarming rate. This breaking was a function of being carved from wood, a porous and fibrous structural tissue.

Today aluminum and structural composite blades are standard, and repairing them when they get dinged has become commonplace. Damage can result from stones and other objects and impact with external objects or the ground.

Repairing a structural composite blade is quite different because instead of just removing material, composite repairs replace material lost to gouges and other damage.

Beyond their obvious weight advantage over aluminum blades, structural composite blades have additional benefits:

A longer service life
The ability to maintain an optimum airfoil shape over the propeller’s service life
An almost infinite fatigue life
An expert can repair most damage
Far more robust when it comes to erosion and impact
Can withstand a lot more impact without affecting its airworthiness
Can be repeatedly restored to factory-new shape and aerodynamics

While the composite materials that form propellers are incredibly durable, they are not entirely immune to operational damage. Propeller manufacturers have created and published protocols to help airplane operators and maintainers determine when and how to repair composite blades.

Overview Of Propeller Issues

Most airplane propeller issues fall into one of two categories: corrosion or physical damage.

Corrosion

One of the most insidious causes of damage to a propeller is corrosion, both external and internal. External corrosion is visible on the blades. Internal corrosion eats at the components within the variable-pitch propeller. Regardless of whether it’s internal or external, corrosion reduces the propeller’s structural integrity, as well as its performance.

Physical Damage

Physical propeller damage include nicks, dings, gouges, and cracks on both the propeller blades and the propeller governor.

A propeller repair shop has the tools to do much more detailed inspections of propellers for cracks, including optical, eddy current, dye penetrant, and magnetic particle inspections. However, routine examinations for damage visible to the naked eye are crucial for good propeller health.

According to the FAA’s Advisory Circular AC 20-37E, “Limited minor repairs may be made on propellers by appropriately rated maintenance technicians either on the aircraft or upon removal of the propeller. Minor dents, cuts, scars, scratches, and nicks may be removed, providing their removal does not weaken the blade, substantially change weight or balance, or otherwise impair its performance.”

Why Repairing Is (Sometimes) Better Than Replacing

There are many valid reasons for repairing rather than replacing. These include:

saving money,
continuing working with a component that is otherwise known to be good,
supporting good mechanics in their business,
and saving the planet from a little more “airplane junk” in the dump.

Aircraft owners should consider all the costs of time, expense, and safety when considering what course to follow while performing maintenance.

Some mechanics prefer replacement over repairing a component. All FAA-licensed mechanics are authorized to do most repairs or replacement tasks, as long as they have the proper training, tools, and documentation.

In truth, most of your aircraft’s components can be repaired by your trusted mechanic, as long as they have the proper training and tools. The question is, should you have the propeller repaired or replaced altogether?

It’s important to consider:

How critical are the components to my safety and the safety of future flights? (Hint: Propellers are VERY important!)
What are the costs of repairing versus replacing (including your own time, shipping costs, and parts/labor)?
How will propellor governor repair versus replacement affect the future reliability (and future maintenance cost) of your aircraft?

All manufacturers publish “time before overhaul” (TBO) guidelines for their propellers. These TBO guidelines are based on both the in-flight hours and the calendar months the propeller has been in service. These guidelines typically range from 1,000 to 3,000 flight hours and five to seven years in service.

The Case For Replacement

So we’ve already covered the main questions on whether to deal with repairing vs. replacing above.

Why else might someone choose to replace a propeller?

You’ve reached your propeller’s operational life limit.
It seems obvious, but it’s imperative to pay attention to your aircraft propeller’s time before overhaul (TBO). Flying your aircraft with propellers beyond their intended service life is inadvisable and potentially dangerous. Overhauling or upgrading your propeller is an investment in your aircraft’s future safety and performance.
You are ready for a dramatic performance increase.
With new propellers, pilots can (potentially) improve aircraft performance with:
- shorter take-off distances,
- lower noise levels,
- better ground clearance,
- reduced tip erosion,
- increased climb rates,
- increased cruise speeds,
- and overall smoother operation.

How Do You Know Which “Flight Path” To Take?

Okay, we’re sorry about that awful pun.

But we’re not sorry about being the best in propeller governor repair or propeller overhauls.

Talk to us. We’re the experts at Stockton Propeller. With decades of experience and free service area pick-up and delivery, we’re the composite propeller experts who keep you flying!

Propeller Inspection Checklist

Why Is Aircraft Propeller Inspection Important?

According to the Aircraft Owners and Pilots Association (AOPA), “the root cause of mechanically induced accidents is almost always neglect.” The AOPA continues:

“On takeoff, propeller tip speeds approach the speed of sound. The blades must absorb not only the punishing vibration of the engine’s power pulses but also vibration caused by the oncoming airstream. Centrifugal loads – those forces that try to pull the blade out of the hub – amount to 10 to 20 tons per blade.

The blades twist and flex. The stresses imposed on the prop are more concentrated in the small areas that are nicked or cut. These nicks and scratches act as stress risers, which can weaken the blade enough to eventually cause it to fail.

When an engine quits, the airplane can glide to a safe landing. When a propeller blade is lost, the resulting imbalance can tear the entire engine from the aircraft, putting the center of gravity far beyond limits and rendering the aircraft uncontrollable.”

That scenario, of course, can be avoided with frequent inspections using this propeller inspection checklist. Performing these routine preflight inspections can clue you into any needed propeller maintenance or repairs.

Stockton Propeller’s Propeller Inspection Checklist

A “walkaround” or preflight visual inspection of your aircraft’s propellers is vital for your plane’s safety and health. Even more important is the safety of you and your passengers or cargo.

An important note: While the term “walkaround” may make it sound like this could be just a superficial glance. However, this should instead be a studied review to gauge your craft’s airworthiness.

To perform a preflight visual propeller inspection, follow these steps:

Get a clear view of the propeller area. In other words, make sure your propellers are clean. In the course of any flight, propellers can pick up dead bugs, dirt, and other pollutants. If your propellers are dirty, it will be challenging to get a good view of any defects. If the propellers are dirty, you can easily wash them off with a simple solution of dish soap and water. If you have to wash off the propeller area, make sure that your propellers are in the down position. This will prevent any liquid from getting into the seals and causing issues there.

Check for surface damage. Carefully and thoroughly examine the aircraft’s propeller blades and other parts for any cracks, nicks, chips, corrosion, or other blemishes. Surface damage can be felt by running a fingernail along the propeller’s edge. For propellers made of wood or composite materials, check for delaminations or microcracks on the propeller surfaces, edges, and glue lines. If your propellers have any drain holes, check that they aren’t clogged. Clogged drain holes can lead to moisture retention and more significant problems down the road.

Check for erosion. Examine the propeller for any and all signs of decay. Look over the paint job on the propeller blades and spinners for any imperfections. This paint on the propeller protects the surface from erosion. If erosion starts to occur, it can be a much more costly fix than having a professional touch up your paint job.

Check for any loose or missing hardware or broken safety wire.

Check for any broken or compromised seals.

Check the straightness of the propeller blades. Perform a simple sight check for any deformations down the edges of the propeller blades. You can determine the straightness of the propeller blades with this simple sight check.

Check for looseness. Flex the propeller blades forward and backward to inspect the intersection for any movement. There should be no movement at all.

Check the hub. Gently shake each propeller blade to feel for blade movement in the hub of the propeller. A small degree – up to ⅛ inch – is allowable. If there is more movement than that, maintenance is needed immediately.

Check for oil or grease leakage. Look for any grease or oil. There should be no oil or grease detected on the propeller blades or spinners. A couple of exceptions are if your propellers are brand new or you are in a hot climate with high RPM conditions.

Update maintenance records. If you notice a small imperfection, make sure to note it in your aircraft’s maintenance records. Your repair person will know when you first saw the issue during a walkaround or preflight inspection. They will also know if the issue gets worse over time.

If, when following this checklist, you don’t see any areas of concern, your propellers are airworthy, and you are good to fly away!

How Often Should You Inspect Your Aircraft’s Propellers?

Before any flight, you should perform the above visual propeller inspection checklist of your aircraft’s propellers.

Then, of course, you should follow the manufacturer’s recommendations for your scheduled overhauls and maintenance. Generally, these schedules are based on years and flight hours.
The recommended Time Between Overhaul (TBO) guidelines are mandatory for Part 135 commercial operators but are only recommended for Part 91 pilots not flying for hire. That being said, Part 91 operators should follow the calendar recommendation for overhaul as a recommendation for inspection/reseal at the 5 or 6 year interval if the prop is less than halfway through the hour recommendation. This gives the prop a good inspection, replaces the aging grease and seals, and gives the blades a clean up and repaint. This will allow the prop to operate safely for another calendar period.

Stockton Propeller is a full-service propeller overhaul and maintenance facility in Northern California with the needed equipment and expertise to perform the needed inspection and service on your propeller. Get inspection and maintenance before a failure happens on your aircraft. Contact us today.

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