17B (B3) Propeller maintenance, storage and preservation

Scope (B3)

• 17.6 Propeller maintenance — level 3: static and dynamic balancing; blade tracking; assessment of blade damage, erosion, corrosion, impact damage, delamination; treatment/repair schemes; propeller engine running.
• 17.7 Storage and preservation — preservation and depreservation.

Level 3 means you must be able to apply the knowledge: interpret limits, choose the correct method and recognise when a propeller must go to an approved propeller workshop.

Routine inspection (daily/pre-flight and scheduled)

• Blades: nicks, cracks, erosion, corrosion, delamination/disbonds (composite and wood), loose or cracked metal tipping (wood), blocked tip drain holes.
• Hub and mounting: security, bolt torque (wood propellers — re-torque at intervals and after storage/humidity change), safety wire, cracks, oil or grease leaks from the hub (constant-speed — leaking seals or a cracked hub, which is serious).
• Spinner and bulkheads: cracks around screws and bulkhead edges, alignment.
• Governor, oil lines, propeller control linkage (full travel, cushion at the stops).
• Logbook: hours and calendar time for overhaul (TBO), Airworthiness Directives and Service Bulletins (e.g. hub crack inspections).

Blade damage assessment

Damage	Assessment and action
Nicks and gouges on metal leading/trailing edges	If within the manufacturer's limits, dress (blend) them out with files and fine abrasive to a smooth, shallow, rounded depression — no sharp edges or stress risers. Inspect with a magnifier/dye penetrant for remaining cracks. Treat and paint. Out of limits → workshop
Erosion	Leading-edge wear from rain/grit; restore profile within limits; composite erosion shields replaced by workshops
Corrosion	Remove pitting within limits, check depth, treat (chemical conversion coating) and repaint; corrosion under decals/de-ice boots and in the hub bore needs attention
Cracks	Unairworthy — remove the propeller
Bent blades / impact (ground strike, sudden stoppage)	Remove the propeller for inspection/overhaul by an approved workshop; the engine must also be inspected per the engine manufacturer (crankshaft flange runout, internal inspection)
Delamination (composite/wood)	Coin-tap test — a dull sound indicates disbond; visual check of bond lines and erosion shield; repair per approved data
Wood-specific	Cracks along grain, separated laminations, worn/charred hub faces (slipping on the flange), elongated bolt holes, warped blades, water damage

Key fact: Field repairs are limited to minor dressing and refinishing within published limits. Straightening bent blades, shortening blades beyond field limits, and hub repairs are workshop tasks.