A propeller is one of the most highly stressed components on an aircraft. During normal operation, 10 to 20 tons of centrifugal force are acting to pull the blades from the hub. The blades are routinely subjected to bending, flexing, and vibratory forces. Damage to a propeller component, such as a stone nick, corrosion, or a ground strike, may act as a stress riser and become the initiation site for a fatique failure which can progress to an abrupt failure of the propeller.
Failure of a propeller blade, clamp, or hub can be many times more severe than an engine failure. In some cases, the vibrations and unbalanced load imparted by the failed propeller have torn the engine from the engine mount, rendering the aircraft uncontrollable. There is also the possibility that a portion of the failed propeller could become a projectile and pierce the aircraft cabin.
Due to the catastrophic nature of a propeller failure, it is essential that the propeller be properly maintained according to the recommended service procedures. The propeller should be inspected and overhauled in accordance with the proper procedures, and at the specified intervals. The propeller should also be inspected before flight to detect impending problems before they become serious. Any grease or oil leakage, loss of air pressure, unusual vibration, or unusual operation should be investigated and repaired as it could be a warning that something serious is wrong.
The following inspections and troubleshooting procedures are provided as guidelines to help the pilot and maintenance personnel discover potential propeller problems. This information can also help the pilot and mechanic maintain the propeller to maximize its useful life. This information is general in nature, and should not be used in lieu of the authorized, published procedures applicable to a specific propeller system.
- Inspect the blades for nicks, gouges. Dress out nicks and gouges before further flight. See "Blade Repairs" for repair instructions.
- Inspect the spinner and visible hub areas for damage or cracks. Repair or replace components as required before further flight.
- Inspect the interior of the spinner (through the blade cutouts) for foreign objects that may have found their
way into the mechanical workings of the propeller.
- Check for loose/missing hardware. Retighten or reinstall as necessary.
WARNING: Abnormal grease leakage can be an indication of a failing hub or blade retention component. An in-flight blade separation can result in a catastrophic aircraft accident.
- Inspect for grease and oil leakage.
- Check blades for radial play or movement of blade tip (in and out or back and forth). See "Loose Blades"
- Inspect de-ice or anti-ice boots (if installed) for damage.
Annual/100 Hour Inspection Procedure
- Remove the spinner.
- Inspect the spinner and visible hub areas for damage or cracks.
- Visually inspect the blades for nicks and cracks.
- Visually inspect the hub parts for damage or wear.
- Check for loose/missing hardware. Retighten or reinstall as necessary.
- Check all visible parts for wear and safety.
- Check for oil and grease leaks.
- Check blade play and blade track.
- Lubricate the propeller assembly. Refer to Hartzell Service Letter HC-SL-61-184 for procedure.
- For feathering propellers which incorporate an air charge in the cylinder, check pressure every 100 hours or once a month, whichever comes first.
- Inspect de-ice or anti-ice boots (if installed) for damage.
The inspections detailed below are made on a regular basis, either before flight, during the 100 hour inspection, or if a problem is noted. Possible corrections to problems discovered during inspections, additional inspections, and limits are detailed in the following inspection procedures.
Inspect the blades for nicks, gouges. Because nicks or gouges can lead to blade failure, dress out nicks and gouges before further flight.
The spinner installed on your aircraft serves three purposes:
- Aerodynamic - the spinner penetrates the air allowing for a smooth redirection of airflow.
- Induction/Cooling - the cone shape of the spinner channels air into the air intake providing adequate cooling and induction.
Inspect the spinner for cracks, missing hardware, or other damage. Refer to Hartzell Manual 127 or an authorized propeller repair station for spinner damage acceptance and repair information.
Grease or Oil Leakage
- A new propeller may leak slightly during the first several hours of operation. Such leakage is normal and should cease within the first ten hours of operation.
- Leakage that persists beyond the first ten hours of operation or occurs on a propeller that has been in service for some time should be referred to an authorized propeller repair station, as this can be an indication of a serious problem.
Instances of abnormal vibration should be investigated immediately. Vibration which occurs only in a certain RPM band, or during a particular flight regime, are not often propeller related. Propeller vibration is normally felt throughout the RPM range, and increases in intensity with RPM. Other components (such as engine mounts or loose landing gear doors) can also be the source of constant vibration.
If the cause of the vibration is not readily apparent, the propeller may be inspected following the procedure below:
- Perform troubleshooting and evaluation of possible sources of vibration in accordance with engine or airframe manufacturer´s instructions.
- Remove the spinner dome.
- Check blade track.
- Manually (by hand) attempt to turn the blades (change pitch). Do not use blade paddles.
- Visually check for bent or damaged blades.
- If abnormal blade conditions (bent, damaged, etc.) are found, the propeller should be referred to an approved propeller repair station before further flight.
- Perform a visual inspection for hub damage. Pay particular attention to the blade retention areas of the hub. If damage is found, or the propeller appears to be leaking grease from a seemingly solid surface, the propeller should be inspected by an approved propeller repair station before further flight.
Checking Blade Track
Check blade track as follows:
- Chock the aircraft wheels securely.
- Refer to Figure 1. Place a fixed reference point beneath the propeller, within 0.25 inch (6.0 mm) of the lowest point of the propeller arc. This reference point may be a flat board with a sheet of paper attached to it. The board may then be blocked up to within 0.25 inch (6.0 mm) of the propeller arc.
Warning: Make certain the engine magneto is grounded (off) before rotating propeller.
- Rotate the propeller by hand (opposite the direction of normal rotation) until a blade points directly at the paper. Mark the position of the blade tip in relation to the paper.
- Repeat this procedure with the remaining blades.
- Tracking tolerance is ± 0.063 inch (±1.60 mm) or 0.125 inch (3.2 mm) total for aluminum blades.
Tracking tolerance is ± 0.125 inch (± 3.2 mm) or 0.250 inch (6.4 mm) total for composite blades.
- A blade track problem can sometimes be caused by foreign matter (such as safety wire) caught between the propeller mounting flange and engine flange. The propeller must be removed to check. If no foreign matter is present, have the propeller checked by an authorized propeller repair station.
Refer to Figure 2. Limits for blade looseness are as follows:
- End Play (leading edge to trailing edge) See Note below
- Fore & Aft Movement (Face to camber See Note below
- In & Out None
- Radial Play (pitch change) ± 0.5o (1o total) measured at reference station
NOTE: Blades are intended to be tight in the propeller, however slight movement is acceptable if the blade returns to its original position when released. Blades with excessive movement, or that don´t return to their original position when released may indicate internal wear or damage which should be referred to an authorized propeller repair station.
Light corrosion on the blades or counterweights may be dressed out (within repair limits) using emery cloth, followed by crocus cloth to eliminate any evidence of the repair. Treat the repaired area to prevent corrosion. Properly apply chromate conversion coating and approved paint to the repaired area before returning the propeller to service.
Hub corrosion of any type, or any heavy corrosion which results in severe pitting, must be referred to an authorized propeller repair station.
Anti-ice / De-ice
Some Hartzell propellers are equipped with an anti-ice or de-ice system. An anti-ice system uses a fluid, typically alcohol, to prevent ice formation. A propeller de-ice system uses electricity to heat a rubber "boot". Both systems are installed only on the inboard portion of a propeller blade (centrifugal force sheds ice that forms outboard on the portion of a propeller blade). It is important not to operate the electrical de-ice system, other than for testing, on the ground. Without adequate airflow there is the possibility of burning out the heating element and causing damage to the propeller blades.
- Remove grease or oil from propeller surfaces by applying Stoddard Solvent or equivalent to a clean cloth and wiping the part clean.
- Wash propeller with a non-corrosive soap solution.
- Thoroughly rinse in water and allow to dry.
Caution: Do not use pressure washing equipment, or caustic/acidic soap solutions, to clean the propeller or control components.
- Clean spinner with a non-corrosive soap solution. Remove grease or oil by applying Stoddard Solvent or equivalent to a clean cloth and wiping the spinner clean.
- Polish the dome (if required) with an automotive-type aluminum polish.
Charging the Propeller
Charge the cylinder with clean, dry air or nitrogen. Nitrogen is the preferred charging medium.
The proper charge pressure is identified on a label located on the flat portion of the spinner under the removable spinner cap, or on the propeller cylinder. Refer to Hartzell Manual 115N (ATA 61-00-15).
Nicks, gouges, and scratches on blade surfaces or on the leading or trailing edges of the blade which are less than 1/32 inch wide or deep may be deferred until the next scheduled maintenance. Larger or deeper damage must be removed prior to flight. Field repair of small nicks and scratches may be performed by qualified personnel in accordance with FAA Advisory Circular 43.13-1A, as well as the procedures specified below.
Local repairs may be made by an A&P mechanic, propeller repairman, or the aircraft builder (experimental), using files, electrical or air powered equipment. Emery cloth and crocus cloth are to be used for final finishing.
Warning: Blades which have been shot peened (as indicated by a "pebble grain" surface) that have damage in the shot peened areas in excess of .015 inch (0.38 mm) deep on the face or camber or 0.250 inch (6.35 mm) on the leading or trailing edges must be removed from service, and the reworked area shot peened before further flight.
Inspect the repaired area with a 10X magnifying glass and dye penetrant. Ensure that no indication of the damage, file marks, or coarse surface finish remain.
Treat the repaired area to prevent corrosion. Properly apply chemical conversion coating and approved paint to the repaired area before returning the blade to service.
Damage to a composite blade must be evaluated and the airworthiness of the blade established in accordance with published criteria. Damage limits may be found in Hartzell Manual 135F (ATA 61-13-35).
Repair of Bent Blades
CAUTION: Do not attempt to "pre-straighten" a blade prior to delivery to an approved propeller repair station. This will cause the blade to be scrapped by the repair station.
Repair of a bent blade or blades is considered a major repair. This type of repair must be accomplished by an approved propeller repair station, and only within approved guidelines.
Painting After Repair
Propeller blades are painted with a durable specialized coating that is resistant to abrasion. If this coating becomes eroded, it is necessary to repaint the blades to provide proper corrosion and erosion protection. Painting should be performed by an authorized propeller repair station in accordance with Hartzell Manual 202A (ATA 61-01-02).
It is permissible to perform a blade touch-up with approved aerosol paint. A listing of approved touch-up paints may be found in the applicable Hartzell Owner´s Manual.
Painting of Blades with Touch-Up Paint
Warning: Cleaning agents (acetone, #700 Lacquer thinner, and MEK), are flammable and toxic to the skin, eyes and respiratory tract. Skin and eye protection is required. For your safety, avoid prolonged contact and use cleaning agents in a well ventilated area.
Using acetone, #700 lacquer thinner, or MEK, wipe the surface of the blade to remove any contaminants.
Feather the existing coatings away from the eroded or repaired area with 120 to 180 grit sandpaper.
NOTE: Erosion damage is typically very similar on all blades in a propeller assembly. If one blade has more extensive damage, e.g. in the tip area, all the blades should be sanded in the tip area to replicate the repair of the most severely damaged blade tip. This practice is essential in maintaining balance after refinishing.
Use acetone, #700 lacquer thinner, or MEK to wipe the surface of the blade. Allow the solvent to evaporate.
Before refinishing the blades, apply a corrosion preventive coating to the bare aluminum surface. Oakite 31, Chromicote L-25, or Alodine 1201 are approved chemical conversion coatings. Apply these coatings in accordance with the directions provided by the product manufacturer.
Mask off deice boot and tip stripes, as needed.
Warning: Finish coatings are flammable and toxic to the skin, eyes and respiratory tract. Skin and eye protection is required. For your safety, avoid prolonged contact and use cleaning agents in a well ventilated area.
Caution: Apply finish coating only to the degree required to uniformly cover the repair/erosion. Avoid excessive paint build-up along the trailing edge to avoid changing blade profile.
Apply the appropriate finish coating to achieve 2 to 4 mils (0.508 - 0.1016 mm) thickness when dry. Re-coat before 30 minutes, or after 48 hours.
Remove masking from tip stripes and re-mask to allow for tip stripe refinishing if required.
Apply the appropriate tip stripe coating to achieve 2 to 4 mils (0.508 - 1.016 mm) thickness when dry. Re-coat before 30 minutes, or after 48 hours.
Remove masking from deice boot and tip stripes if required.
Optionally, perform dynamic balancing in accordance with the procedures and limitations specified below, as well as those in Hartzell Manual 202A (ATA 61-01-02), Standard Practices Manual and the airframe manufacturers instructions.
All propellers are statically balanced when new, overhauled, or after a major repair. Dynamic balancing reduces vibration caused by the entire rotating system (engine and propeller) and can help prolong the life of the propeller, engine, airframe, and avionics.
Dynamic balancing is strongly recommended, but not required unless specified by the airframe or engine manufacturer.
The propeller should be dynamically balanced to 0.2 IPS (0.508 CPS) or lower. A lower reading is desirable, but if the propeller cannot be balanced to 0.2 IPS (0.508 CPS), it must be removed and the static balance of the propeller checked and corrected.
Do not exceed a maximum weight per location of 0.9 oz. (25.5 g). This is approximately equal to six AN970 style washers (0.188 inch I.D., 0.875 inch O.D., 0.063 inch thickness) (4.76 mm I.D., 22.23 mm O.D., 1.59 mm thickness).
NOTE: It may be necessary to alter the number and\or location of static balance weights in order to achieve dynamic balance.
Record the number and location of dynamic balance weights, and static balance weights if they have been reconfigured, in the logbook.
Following propeller installation of maintenance, the propeller system must be purged of air and proper operation verified.
- Perform engine start and warm-up per the Pilot´s Operating Handbook (POH).
- Cycle the propeller control throughout its operating range from low to high blade pitch (or as directed by the POH).
- Repeat this procedure at least three times to purge air from the propeller hydraulic system and to introduce warmed oil to the cylinder. NOTE: Pitch change response on the first operation from low to high blade pitch may be slow, but should speed up on subsequent operations.
- Verify precise RPM control from low pitch to high pitch for various engine power ranges.
- Shut down the engine in accordance with the POH. NOTE: Air trapped within the propeller hydraulic cylinder will cause pitch control to be imprecise and may result in propeller surging.
After engine shutdown, check propeller for signs of engine oil leakage.
Operational Check - Static RPM Check (Reciprocating Engines Only)
- This operational check should be performed after installation, maintenance, or propeller adjustment.
- A calibrated tachometer must be used to ensure the accuracy of the RPM check.
- Back the governor Maximum RPM Stop out one turn.
- Advance the propeller control lever to MAX (max RPM), then retard the control lever one inch (2.5 cm).
- Set the brakes and chock the aircraft or tie aircraft down.
- Start the engine.
- SLOWLY advance the throttle to maximum manifold pressure.
- Slowly advance the propeller control lever until the engine speed stabilizes.
- If engine speed stabilizes at the rated RPM to 50 RPM lower than the rated RPM (or as required by the aircraft manufacturer) then the low pitch stop is set correctly.
- If engine speed stabilizes above/or below the rated RPM, the low pitch stop requires adjustment. Refer the low pitch stop adjustment to an authorized propeller repair station. The low pitch stop must be set for the rated RPM or 50 RPM lower than the rated rpm (as required by the aircraft manufacturer).
- Stop the engine.
- Return the governor Maximum RPM Stop to the original position, or adjust the governor to the rated RPM with the Maximum RPM Stop screw.