e. Inspection and Maintenance by the Owner/Operator. Notwithstanding the other requirements stated herein, it is incumbent on the owner/operator to inspect and conduct routine maintenance on his/her propeller. This document and others cited in this AC provide guidelines for doing such maintenance.
f. Propeller Records. Maintenance records are a required part of aircraft maintenance.
Propeller maintenance recordkeeping responsibility is ultimately assigned to the owner/operator of aircraft operated under 14 CFR part 91 in accordance with part 91, section 91.403.
Section 91.417 requires a record of maintenance, including a record of total time in service and time since last overhaul for propellers required to be overhauled on a specific time basis, for each propeller. A propeller logbook is an appropriate document for recording total time in service and time since overhaul. In some cases, lack of records may require premature maintenance activity, overhaul, or possible retirement since most ADs presume if the time in service and time since overhaul is not known, the propeller requires compliance with the most restrictive level called out in the AD. Propeller logbooks are available from various sources, including the propeller manufacturer. Damage as well as details of maintenance to the propeller should be entered into the logbook. The total time in service and time since the last overhaul recorded in the propeller logbook should be updated at minimum at the time of annual inspection when reviewing the aircraft operating maintenance records.
201. CLEANING. Proper cleaning of the propeller is critical to maintaining its continued airworthiness. Care should be taken in cleaning all propeller surfaces to prevent damaging the surface being cleaned. Many propeller surfaces have finish requirements that can be damaged by harsh brushing, cleaning agents, and handling. Other surfaces have special finish textures such as shot or glass bead peening that can be harmed by abrasion or polishing with steel wool or other abrasive materials. In addition, special corrosion protection finishes such as lacquer, paint, or anodizing can be inadvertently removed during cleaning. Use of high-pressure washers is not recommended to clean propellers because the high pressure may drive water under seals and into the hub and other cavities in the propeller. Once the water enters the propeller, it can establish a corrosive internal environment. Alkaline and acidic solutions and strippers for routine cleaning should also be avoided.
NOTE: If any oil or grease is evident on the propeller, the source of the leak should be determined before cleaning si nce the oil or grease may be leaking from a crack, seal, or lubrication fitting (see Figure 2-1).
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FIGURE 2-1.
Grease Leak Residues
a. Cleaning. Cleaning should be done with clean water and a non-alkaline cleaner.
b. Post-Cleaning. Rinse the propeller with clean water, dry with a soft cloth.
202. INSPECTION METHODS. The methods used in propeller inspection are versions of methods used in inspecting the entire aircraft. These methods have precisely determined probabilities that, if a defect exists, it will be detected. This reliability of detection of defects permits inspection intervals to be established. To ensure that a component will remain airworthy, it is necessary that the inspection used to detect defects in that component be accurately and reliably accomplished. This process requires that all inspections of the same part on a propeller be performed in a uniform manner to ensure the appropriate probability of detection of a defect. The inspector should be trained in the method and the inspection device used should be in good condition and calibrated as required. A detailed procedure should be used. A more detailed discussion of the requirements for satisfactory inspection may be contained in the propeller manufacturer’s maintenance documents. All inspections, other than visual, must be conducted in an appropriately rated repair station.
a. Visual Inspection. The primary defense against early failure of propellers. When inspecting propellers, it is necessary to use touch and other senses, as well as visual cues.
Changes in surface roughness, unusual free play, and odd sounds give hints as to conditions that may affect airworthiness. Feel for roughness and look for small variations in color, texture changes, waviness, and changes in reflection that may signal the removal of protective coatings.
Some areas may require the use of a 10x magnifying glass to identify small features or find cracking. Refer to the propeller manufacturer’s maintenance documents for specific instructions.
b. Penetrant Inspection. Fluorescent penetrant is far superior to non-fluorescing penetrant (visible die penetrant), particularly for detecting small surface cracks on propeller blades. The use of visible die penetrant is not recommended. Cleaning is vital to ensure reliable detection and the absence of false indications. Sometimes, manufacturers recommend specialized cleaning Par 201 Page 9
procedures involving media blasting and etch. Such procedures, if called for, are beyond the capabilities of most maintenance personnel and maintenance organizations not specifically FAA- certificated to accomplish them. Penetrant inspection on propellers is conducted in a rated repair station. Refer to the propeller manufacturer’s maintenance documents for special instructions.
c. Ultrasonic Inspection. Ultrasonic inspection uses specialized equipment to send, receive, and process sound waves to detect flaws on or below the surface of the component being tested. Appropriately certified inspectors conduct ultrasonic inspections. Ultrasonic inspections are very specific and require specially designed probes and calibration standards to obtain reliable results. Ultrasonic inspections can be conducted on composites, wood, ferrous, and nonferrous metals. Refer to the propeller manufacturer’s maintenance documents for special instructions.
d. Eddy Current Inspection. Eddy current inspection uses specialized equipment to generate and measure an electric field that detects flaws at or slightly below the surface of the component being inspected. Eddy current inspection is conducted by appropriately certificated inspectors. This type of inspection is very specific and requires specially designed probes and calibration standards to obtain reliable results. Eddy current inspection is used on ferrous and non-ferrous metals. Refer to the propeller manufacturer’s maintenance documents for special instructions.
e. Magnetic Particle Inspection. Magnetic particle inspection is conducted at an appropriately rated repair station. It is useful for finding cracks, inclusions, and imperfections at or near the surface of ferrous parts. Refer to the propeller manufacturer’s maintenance documents for special instructions.
203. TYPES OF INSPECTION. The paragraphs below describe non-destructive inspection and visual inspection techniques that have been adapted to, or are unique to, the propeller.
a. Inspection After Suspected Impact. Propellers that have been involved in a known or suspected static or rotating impact with relatively solid objects (e.g., ground, maintenance stands, runway lights, birds, etc.) or relatively yielding objects (e.g., snow banks, puddles of water, heavy accumulation of slush, etc.) should be inspected for damage in accordance with the manufacturer’s maintenance manual before further flight. If the inspection reveals one or more of the following listed indications, the propeller should be removed and sent to an appropriately rated repair station.
(1) A bent or twisted blade.
(2) A blade that tracks out of limits.
(3) A loose blade in the hub for blades that are not normally loose in the hub.
(4) Any noticeable or suspected damage to the pitch change mechanism.
(5) Any diameter reduction (tip damage).
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(6) A tracking alignment error.
(7) Visible major damage such as nicks, gouges, corrosion or cracks.
(8) Operating changes, such as vibration or oil or grease leak
b. Propeller Tracking Inspection.
(1) Evaluating propeller blade tracking can indicate much information about propeller condition. Accurate propeller tracking requires securing the aircraft in a stationary position and ensuring that the engine propeller shaft is tight against the thrust bearing. A blade-tracking datum can be made simply by placing a block on the ground in front of the aircraft in the propeller arc. Raise the block as required to obtain a clearance between the blade tip (blade vertical) and the datum block not exceeding 1/4-inch. Another method is to raise a block in front of the propeller with a small gap. A cowling fixture can be used as well. In some aircraft, it may be necessary to relieve engine compression (loosen spark plugs) and seek a calm day to eliminate outside disturbances that would cause an apparent tracking error. Draw a line on the block next to the blade tip position. Move the blade in a fore-and-aft direction and mark the limits of such motion. Pull all the blades past the drawn datum, checking fore-and-aft free play as before. No blade should deviate more than 1/16-inch from the plane of rotation, as defined by the drawn marks, unless the manufacturer’s service manuals define greater limits. Record any abnormal condition in the propeller log.
(2) It should be noted that some propeller blades require centrifugal load to seat properly in the hub so propellers of this type will show a large amount of free play. Follow the manufacturer’s tracking inspection instructions for these propellers. Blade-to-blade tracking difference could indicate a deformed blade. Free play differences on blades may indicate internal blade bearing, preload system, or actuating pin problems. Safety practices, such as ensuring that switches are off, or grounding the magnetos, are necessary to ensure that rotating the propeller does not cause the engine to start during the tracking inspection (see Figure 2-2). A repair station should not return propeller blades that exhibit any looseness or out-of-track conditions exceeding 1/16-inch (or the manufacturer’s specification) to service without inspection/repair.
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FIGURE 2-2.
Propeller Tracking (Wood Block or Cowling Fixture Shown)
c. Propeller Overspeed Inspection. Generally, propeller overspeed causes no visible external damage to the propeller. In the event of an overspeed event, the manufacturer’s instructions should be followed. These instructions usually contain permissible transient overspeed and overspeed limits above which the propeller must be removed and sent to a repair station. The problem that caused the permissible transient overspeed condition should be corrected since the propeller is not designed to be routinely operated at the transient overspeed limit.
d. Inspection for Corrosion. Corrosion may be present on the propeller in varying amounts. Prior to performing any inspection process, maintenance personnel should determine the specific type and extent of the corrosion and become familiar with the propeller manufacturer’s recommended corrosion removal limitations and practices.
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e. Inspection of Aluminum Blades. For aluminum blades, conduct a thorough visual inspection per the manufacturer’s maintenance document. If blade damage is beyond that specified for field repair, the blade must either be retired or sent to a repair station for evaluation before further flight.
f. Inspection of Composite (Including Wooden) Blades. For composite blades, a thorough visual inspection is recommended together with a coin tap inspection of each composite blade, including the metal erosion shield on the leading edge (see AC 43-3, Nondestructive Inspection for Aircraft, or follow the manufacturer’s instructions for coin tap test limits so as not to damage the blade). Repair damage, delaminations, or debonds within the limits specified. If blade damage is beyond that specified by the manufacturer for minor repair, the blade must either be retired or sent to a repair station for evaluation before further service.
g. Inspection for Lightning Strike on Composite Blades. Any composite blade suspected of lightning strike should be inspected and may require overhaul. Lightning strikes usually enter a composite blade through the metal erosion shield. If the blade has a metallic lightning screen or tip lightning strip, the lightning strike may enter the screen or through the tip instead of the erosion shield. If a lightning strike is present, a darkened area and possible pitting, usually in the proximity of the tip, will be noticeable. If a lightning strike is suspected or detected, follow the manufacturer’s service instructions before further flight.
204. INSPECTION LEVELS.
a. Three Levels of Inspection. To ensure airworthiness, propeller inspection may be accomplished at three levels:
(1) Preflight or walk-around inspection, detailed inspection (such as a 100-hour or annual inspection), and teardown inspection (or overhaul).
(2) These levels correspond to three of the four inspection levels carried out on airframes. Regardless of the level of inspection, the inspection should follow a standard procedure to be carried out in a similar fashion every time it is accomplished. The major elements of any inspection include the following:
(a) Basis for the Inspection. Purpose, documents needed, inspection frequency, and what is needed to accomplish the inspection.
(b) Preparation. Cleaning, surface preparation, equipment and calibration requirements, etc.
(c) Implementation. Define what the inspection is and how it is to be carried out, defect criteria, post-cleaning, etc.
(d) Evaluation. Accept/reject criteria, reporting.
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b. Preflight/Walk-Around Inspection. The propeller portion of the walk-around is an important element of the process of airworthiness maintenance. It should not be merely a superficial look, but a studied review of the condition of everything that might give trouble during the forthcoming flight.
(1) Blade. The blade and its surface should be carefully inspected for conditions affecting airworthiness as detailed below.
(a) Surface Damage. Look for surface damage on both sides of the blades such as dents, nicks, scratches, and corrosion. Surface imperfections can also be felt by running your fingernail along the blade leading edge. Damage should be repaired before flight. Whenever a noticeable dent, nick, corrosion pit, or bump is observed, an appropriately rated mechanic should blend it out. The mechanic should remove all corrosion products and determine that the section thickness has not been reduced below allowable limits. Allowable thickness limits should be obtained from the manufacturer’s maintenance manual, or other FAA acceptable propeller inspection criteria.
(b) Erosion. Examine the blade for evidence of erosion. If metallic blades appear to show erosion beyond limits, the propeller should be removed from service and evaluated by an appropriately rated repair station. Check the condition of the paint on blades and spinners that have protective paint. Paint protects the surface of the blade from erosion, and the blade should be repaired before the paint wears through and the blade structure begins to erode. Do not apply excessive paint and do not paint propeller components unless it is in accordance with manufacturer’s instructions since improper painting may affect propeller balance, operation, static electricity discharge, or have other unintended consequences.
(c) Composite or Wood Delaminations. Although not susceptible to corrosion like metal propellers, wood or composite propellers have special problems that can lead to an unairworthy condition. Wood or composite propellers are susceptible to internal damage from small stone strikes that can create delamination or microcracks and permit intrusion of moisture.
Moisture will cause expansion of existing cracks and delaminations. When moisture freezes within the blade, it causes delamination. When inspecting wood or composite propeller blades, look for cracks or delamination on the blade surface and at blade edges. In wooden propellers, check the gluelines for debonding; look for warp and loss of protective coating (paint or varnish). If drain holes are present, it is imperative that they be inspected since they may become clogged with insects and debris. Clogged drain holes can cause moisture retention.
(d) Straightness. Sight down the edges to find any deformation.
(e) Looseness. Feel the blades and move them to find unusual changes in looseness and unusual play. Blade-to-blade differences indicate that an internal problem may exist. Some propeller blades are designed to be loose. In this case, look for blade-to-blade differences to indicate unusual play.
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(f) De-Icing System. Check the de-ice or anti-ice boots, if installed, for good adhesion to the propeller. Examine the boots and exposed wiring for breaks and burn through (see Figure 2-3).
FIGURE 2-3.
Heater Edge Debond
(g) Sheath Cracks and Debonds. Check the leading edge erosion sheath of wood or composite blades, if installed, for cracks and debonds. If damaged, repair before further flight or follow the manufacturer’s recommendations for permissible limits on cracked or debonded leading edge erosion sheaths (see Figure 2-4).
FIGURE 2-4.
Sheath Crack
(2) Oil and Grease Leakage. Look for oil or lubricant leaks in unusual places, like the outside surfaces and seals. Oil or grease leakage may be due to a seal failure or a crack. The source of the oil or grease leak should be determined before flight. During maintenance, wipe the surfaces of the propeller after this inspection, not before, since oil leaking from a crack may assist in detecting it. Some manufacturers fill hubs with red oil that gives a positive warning of a crack in the hub.
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(3) Spinner and Bulkhead. Externally check the spinner and bulkhead for security, missing fasteners, damage, and cracks. Cracks typically originate from the attachment screws.
Cracks should be serviced in accordance with the manufacturer’s manuals. Check for looseness of the bulkhead. This could be an indication that the mounting bolts are loose.
(4) General Condition. Look for loose wires, grease fittings, and debris.
(5) Control System. The control system (governor) of a controllable pitch propeller should be checked to determine whether the system is operating properly and is not leaking.
(6) Maintenance Records. Note any indications in th e logbook for future reference to determine whether a condition is getting worse.
c. Detailed Inspection (Such as at a 100-Hour or Annual Inspection). A more rigorous visual inspection can detect some conditions affecting airworthiness of propellers, particularly from external sources of damage, such as erosion, de-icing boot damage, and blade tracking.
Many locations encountering damage are hidden. For these areas, conducting a worthwhile inspection will require some disassembly and special equipment. Such an inspection is a detailed inspection and may be accomplished in the field by appropriately rated maintenance technicians. Generally speaking, a detailed inspection requires removal of the spinner and certain other components as indicated below. Propellers suspected of more severe damage may require removal from the aircraft and the next level of inspection - a teardown inspection.
(1) Inspection Interval. Most manufacturers require a periodic inspection at fixed intervals, usually between 1 and 2 years or 100 to 300 flight-hours, whichever is sooner. A detailed propeller inspection is done at each aircraft annual inspection, or as required in the aircraft maintenance procedures. This inspection reduces the possibility that a propeller will be neglected and subjected to unobserved corrosion and other damage.
(2) Fixed-Pitch Propeller. The detailed inspection uses a procedure similar to that used in the walk-around inspection, but more time and closer scrutiny is required. Inspect the propeller section-by-section (if it is a large propeller, consider marking off sections to ensure complete coverage). Use the best possible light and use a 10X magnifier for any questionable areas. Look for cracks and corrosion pitting that may have escaped earlier scrutiny. The magnifier is a great help in determining whether a scratch is, in fact, a crack. All applicable propeller ADs must be checked for compliance. The following detailed inspections are recommended.
(a) Propeller Blades. Visually inspect for excessive wear and erosion, damage, nicks, cracks, corrosion, lightning strike, ground strike.
1 Check for distortion, security to the engine, and tip tracking. Check the adequacy of protective coatings, paint, and plating.
2 Check the leading edge erosion shield for damage, debonding, and cracks.
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3 Check composite and wood blades for delaminations, surface cracks, and exposed composite.
(b) Spinner and Bulkhead Assembly. Detailed inspection procedures require removal of the propeller spinner for examination of the hub area. Inspect the spinner and spinner bulkhead for cracks and repairs such as stopdrill holes and weldments. Spinner bulkhead attachment tabs frequently succumb to fatigue and should be checked. It is good practice to remove the spinner after each 100 flight-hours to observe the propeller-to-engine attachment. If repairs are present, they should conform to the manufacturer’s maintenance documents.
1 Visually inspect for cracks, wear and abrasion, loose or missing attachment bolts or screws, large dents, excessive screw hole wear, and loose or missing retaining hardware.
2 Check cowl-to-spinner fit for damage and interference.
(c) Propeller Assembly.
1 Examine propeller attach bolts for looseness, missing safety wires, and cracks.
Cracked or broken bolts may be the result of overtorquing. Correct torquing procedures are given in the manufacturer’s service instructions. The use of dry or lubricated bolt threads for torquing purposes is not standardized and may change from one engine to another using the same propeller. Cracks may be present in the hub area between or adjacent to bolt holes and along the hub pilot bore. Cracks in these areas cannot be repaired and require immediate removal of the propeller.
(aa) Visually inspect for cracks, corrosion, nicks, and damage.
(bb) Check the attaching bolt for improper torquing and improper safety.
(cc) Check the condition of fasteners, tie-wires, clips, and etc.
(dd) Check the adequacy of protective coatings, paint, and plating.
2 Conduct a functional check including revolutions per minute (RPM) control, RPM limits, idle setting, responsiveness, and vibration.
(3) Controllable Pitch/Constant Speed. A complete detailed inspection of controllable pitch propellers requires removal of the spinner for examination and servicing of the propeller hub and blade clamp area. All inspection and servicing of the pitch control mechanism should follow the recommendations of the propeller, engine, and airframe manufacturer. All propeller ADs must be checked for compliance.
(a) Propeller Blades.
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1 Visually inspect for excessive wear and erosion, damage, nicks, cracks, corrosion, lightning strike, and ground strike.
2 Check for distortion, looseness, and pitch tip travel.
3 Check the adequacy of protective coatings, paint, and plating.
4 Check the leading edge erosion shield for damage, debonding, and cracks.
5 Check composite blades for delaminations, surface cracks, and exposed composite.
6 Perform tip tracking procedures.
(b) Spinner and Bulkhead Assembly. Detailed inspection procedures require removal of the propeller spinner for examination of the hub and blade retention area. Inspect the spinner and spinner bulkhead for cracks and repairs, such as stopdrill holes and weldments.
Spinner bulkhead attachment tabs and bolts frequently succumb to fatigue and should be checked. It is good practice to remove the spinner every 100 hours to observe the hub and blade retention area. If repairs are present, they should conform to the manufacturer’s maintenance documents.
1 Visually inspect for cracks, wear and abrasion, loose or missing attachment bolts or screws, large dents, excessive screw hole wear, and loose or missing retaining hardware.
2 Check cowl-to-spinner fit for damage and interference that could affect propeller operation.
3 Check the security of balance weights.
(c) Propeller Assembly. Propeller attach bolts should be examined for looseness, missing safety wires, and cracks. Cracked or broken bolts are usually the result of overtorquing.
Correct torquing procedures are given in the manufacturer’s service instructions. The use of dry or lubricated bolt threads is not standardized and may change from one engine to another that use the same propeller.
1 Visually inspect for cracks, corrosion, nicks, damage, oil and grease leaks.
2 Check attaching bolt for improper torquing and improper safety ties and tabs.
3 Check the condition of fasteners, tie wires, clips, etc.
4 Check adequacy of protective coatings, paint, and plating.
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5 Conduct a functional check including RPM control, RPM limits, idle setting, ability to feather, responsiveness, and vibration.
6 Check oil or grease for water and contamination with corrosion by products.
7 Examine the hub area for oil and grease leaks, missing lubrication fittings, and missing lubrication covers.
(d) Hub, Piston, Cylinder, Dome, Blade Clamps. The hub and associated clamps, as well as pitch change mechanisms, should be inspected for corrosion from all sources, including rain, snow, and bird droppings that may have entered through spinner openings. On propeller models with blade clamps, when servicing the propeller thrust bearings through lubrication fittings in the blade clamps, the rear lubrication fitting on each clamp must be removed to avoid extruding grease past the bearing grease seal and damaging the seal. Look for water or discolored grease exiting the rear lubrication fitting. If clear or discolored water is present, it may be a sign of corrosion in the hub. Protective covers should be pressed over the ends of all lubrication fittings. Check the blade seals for leakage. Propeller domes, pistons, and cylinders should be checked for leaks at the seals and on the gas fill valve (if so equipped).
Cracks may be present in the hub and retention area. Cracks in these areas cannot be repaired and require immediate removal of the propeller from further service.
(e) Pitch-Change Mechanisms. Fiber block pitch-change mechanisms should be inspected for deterioration, fit, and the security of the pitch-clamp forks.
1 Check all connections and cable routings between propeller governor and cockpit control.
2 Inspect for propeller operation, insecure mounting, binding, and restricted travel.
(f) Feathering Mechanisms. Certain models of full-feathering propellers use spring-loaded pins to retain the feathered blade position. Spring and pin units should be cleaned, inspected, and re-lubricated as per the manufacturer’s recommendations and applicable ADs.
Certain propeller models use an air charge for feathering. This should be checked for proper air pressure.
(g) Counterweights. Pitch change counterweights on blades or blade clamps should be inspected for security, cracks, corrosion, and to ensure that adequate counterweight clearance exists within the spinner.
(h) De-Icing and Anti-Icing Devices.
1 Check the condition of rubber boots for damage, erosion, and attachment.
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