aircraft propeller maintenance procedures

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.

Preventing Corrosion with Propeller Maintenance

Aircraft propeller maintenance procedures are strict and rigid – and for a good reason. Ensuring that the propellers of any craft are in optimum condition is essential for maintaining onboard safety. Propeller inspection is a vital part of this, as is taking measures to prevent damage and issues.

Corrosion is one of the most significant factors in the deterioration of propellers, and this can be expensive and dangerous. Luckily for you, here at Stockton Propeller, we make it our mission to keep you informed and educated. In turn, this means you can keep your aircraft in tip-top condition for longer.

What Is Corrosion?

In the simplest terms, ‘corrosion’ refers to the breakdown of a material – usually metal – due to a chemical reaction. Typically, this will involve the oxidation of metals with air or water molecules.

Corrosion can also occur when an acidic or base material comes into contact with something else. Corrosion impacts the physical properties of a material, making it weaker or less effective.

When it comes to aircraft, this can be very dangerous.

What Are Common Types of Propeller Corrosion?

There are many causes of aircraft propeller corrosion. Familiarising yourself with the most common will help you prevent them. These most common corrosion causes include:

1. Uniform Surface Attack

The most common type of corrosion, uniform surface corrosion, is caused by the metal’s exposure to the oxygen in the air. Uniform surface attacks usually occur where paint wears away from the surface.

Decay will be accelerated if the surface is not adequately prepared before painting. It can also be exacerbated if the propeller is exposed to high humidity, acids, or pollutants.

2. Intergranular Corrosion

This type of corrosion is less common but more disastrous. Once you have discovered it, it is usually too late to save the propeller.

Intergranular corrosion occurs between the grains or crystals of the materials and may appear in the presence of tensile stress. Here, cracks may occur along grain boundaries, and progress along the paths until total decay occurs.

This type of corrosion usually occurs as a result of chromium depletion and can be avoided using materials with less than 0.05% carbon.

3. Stress Corrosion

Stress corrosion is prevalent in highly stressed areas of the aircraft, such as propellers, engine crankshafts, or landing gears. Scratches or corrosion to the metal surface is usually the primary cause and can result in the component’s failure.

4. Crevice or Deposit Corrosion

Another common form of corrosion is a crevice, or deposit, corrosion, and can occur anywhere, which traps pollutants or moisture. Rivets and lapped skin joints are prime examples, and this can result in a weakening of the entire structure if left untreated.

5. Filiform Corrosion

The first sign of this is usually fine, worm-like lines or corrosion which show up under paintwork. Over time, this will turn into a bubbling, flaking surface, leading to long-term damage. Filiform corrosion is most commonly found on aluminum or magnesium surfaces, which have been inadequately prepared for polyethylene paints.

Reduce the Risk of Corrosion with Aircraft Propeller Maintenance Procedures

Corrosion can be catastrophic to an aircraft, especially when it occurs on the propeller. These are the heart of the craft, and a failure here can lead to tragedy in the air. Fortunately, there are steps you can take to help reduce the risk of corrosion, and these revolve around proper maintenance.

Wash Your Aircraft

Taking a little time to wash and care for your craft can really pay off in the long run. If you have undergone a long flight, make sure you rinse off the aircraft to remove any corroding agents.

Take extra time and care on propellers, do not use a pressure washer, and make sure these are treated with corrosion inhibitor products where appropriate.

Cleaning your propeller blades properly can help to increase their lifespan, and well as reducing corrosion. Different materials will have different requirements, as follows:

Aluminum and steel propellers should avoid caustic or acidic materials, as well as steel brushes, steel wool, or power buffers. Instead, use a brush or cloth with a suitable cleaning solvent, and add a suitable polish if required. Once clean, coat the propellers in engine oil.
Wooden propellers need warm water and mild soap, with a cloth or brush.
Remember to rinse in freshwater as soon as possible if it has been in contact with salt water, and thoroughly dry once finished.

Use Covers

Covering your aircraft helps to protect it from the elements, and this can also be applied to propellers. Investing in quality propeller covers allows you to increase the lifespan of these parts and keep them safe from corrosive factors.

Keep The Aircraft As Dry As Possible

Staying dry can be easier said than done if you live in a damp climate, but it is essential to try. Make sure your craft is dried off thoroughly, and don’t leave propellers to simply ‘drip-dry.’

Carry Out Regular Propeller Inspections

Ultimately, implementing a strict, regular inspection and maintenance program is the easiest way to reduce corrosion. A scheduled propeller inspection plan will allow you to get to know the aircraft, flagging up any inconsistencies or changes immediately. It also allows you to treat corrosion as it arises, rather than leaving it to spread.

What Is Involved In A Propeller Inspection?

A regular inspection should include a visual overview of the propeller and any other security features. As a rule, you should check:

Propeller blades and spinners for any grease deposits or the presence of excessive oils
Weld and braze sections for evidence of weakness or failure
For any scratches, nicks, or flaws on the propeller.
Bolts and screws for tightness and proper safety.
Ensure oil levels and lubricating requirements are sufficient.

Preventing Corrosion with Propeller Maintenance

Learning to undertake regular, thorough maintenance and inspections are crucial elements of owning an aircraft. At Stockton Propeller, we have the skills, experience, and equipment you need to keep your propellers in the best condition.

Get in touch today, and ask one of our experts how we can help keep your craft airborne for longer.

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