Prop Preflights: Spotting the Damage

We’re all guilty at one point or another. There’s more to properly preflighting a prop than quickly running a finger along the leading edge of the blades to feel for imperfections. Moreover, if you do look closely at the prop before putting the power to it, do you really know what you’re looking at? 

Walking away from my visit at Sensenich Propeller Services—and walking around my community hangar and eyeballing some pretty atrocious-looking props—has opened my eyes to the level of abuse our props endure. It’s ugly.

Start your preflight by grabbing hold of the spinner and make sure it’s tight and isn’t missing hardware. Grab the blades and make sure they don’t wobble in the hub. I found just that after parking on a transient ramp for a week. I made the wise choice of not flying the airplane home because it turned out one of the three blades was used to pull the airplane out of the tiedown spot. Use a towbar, instead. Run a hand down the leading edge while looking and feeling for stone nicks (v-shaped nicks can cause stress risers and  failure of the blade tip). 

While you’re looking at the blades, start at the hub and look for grease—a sign of damaged seals. Periodically clean the blades so you can easily spot new leaks. Hartzell suggests a simple solution of dish soap and water to gently remove bugs, dirt and pollutants from the blade’s surface. But use caution in spraying water directly into the hub, which can trash the seals. 

No matter how well you care for a prop it will never be as pretty as it is the day it comes out of overhaul. It will develop nicks, which are sharp notch-like displacements of the blade’s leading and trailing edge. What you have here is the start of cracks in the blade.  And if you spot any cracks, they are grounds for immediate removal of the prop for a detailed inspection. While rare, you might also spot dents in the blade. Dents can cause local stress risers around their perimeter and under the surface. Leave your body filler in the toolbox—that’s not an approved or effective repair.   

The most common flaw on a blade is erosion. This is actually the loss of material from the blade’s surface, and is more common on the leading edge close to the tip. The problem with excessive erosion is the setup for eventual corrosion. Keep the engine power as low as you can when taxiing on unfamiliar surfaces, and that also includes avoiding Beta in a turboprop.  

Don’t underestimate lightning strike damage, especially if you park outside. Evidence that a metal blade was zapped might include burned and melted areas or even a trail of small pits along the blade’s surface. 

A good source of propeller upkeep info comes from the FAA’s AC 20-37E , which reinforces that only rated maintenance techs can perform any minor repairs (including filing, sanding, filling and painting) to a propeller. Keep the plane parked and lobby their help if you spot questionable damage. 

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Editor in Chief Larry Anglisano has been a staple at Aviation Consumer since 1995. An active land, sea and glider pilot, Larry has over 30 years’ experience as an avionics repairman and flight test pilot. He’s the editorial director overseeing sister publications Aviation Safety magazine, IFR magazine and is a regular contributor to KITPLANES magazine with his Avionics Bootcamp column. When he’s not writing, Larry is working on a collection of guitar compositions for the upcoming Flying n’ Jazz production.