4-3 inspection for delamination and internal damage of composite components, x-ray inspection for internal damage, and fluorescent penetrant or magnetic particle inspection of metallic components.
4.4.6 Pass Fail Criteria.
Section 35.36 requires that bird impact on a “typical installation” does not cause a major or hazardous propeller effect. Composite propeller blades and the associated airplane installation may have inherent mitigating features that would permit the release of some debris due to bird impact.
For twin-engine airplanes, release of debris without sufficient energy to penetrate a fuselage may be acceptable.
For nose mounted single engine tractor installations, propeller fragments caused by bird impact would not hit the fuselage and cause damage to the airplane.
Unbalanced loads that do not cause damage to the airplane or engine may be acceptable. When showing compliance to § 35.36, the FAA recommends that the applicant identify the amount of blade loss, if any. That information should be included in the installation manual provided to airframe manufacturers for aircraft testing.
4.5 Section 35.37, Fatigue limits and evaluation.
See AC 35.37-1 for guidance on propeller fatigue limits and evaluation.
4.6 Section 35.38, Lightning strike.
AC 35.23-1 addresses the effects of lightning on electronic controls. This guidance provides an overview of test methodology used to determine the effect of a lightning strike on a propeller. See AC 20-53, AC 20-136, AC 20-155, and RTCA/DO-160 for information on detailed methods, test set-up information on voltage waveforms, current waveforms, and data collection for conducting a lightning strike test.
4.6.1 Lightning Path.
Applicants should consider all components of the propeller assembly that could be in the lightning path. These include, but are not limited to, the spinner, blade, hub, blade bearings, and the pitch change mechanism. Additionally, electrical or electronic components that could be influenced by indirect effects should be considered, such as propeller blade, spinner de-icing system components, and any other propeller mounted electrical or electronic components.
4.6.2 Direct or Indirect.
Applicants should consider whether the damage caused by lightning is characterized as direct or indirect.
Direct effects associated with lightning depend on the physical damage caused to the structural component involved, attachment point, and current path through the structure. This damage depends on the strength of the strike and on the construction of the propeller races and bearings.
4-4 Indirect effects are classified as damage to electrical equipment by the current or voltages either by the associated electromagnetic field, surges, or by current directly injected into the electrical wires.
4.6.3 Indirect Lightning Strike.
Testing for indirect effects determines the conducted currents, surge voltages, and induced voltages entering the aircraft electrical system through systems, such as the propeller de-icing system. Testing involves measurement of voltages at the terminals of the de-icing system or other electrical or electronic systems where they connect to the aircraft electrical system.
4.6.4 Direct Lightning Strike Damage.
The damage evaluation for blades, including composite blades, after a lightning strike typically includes a combination of visual examination, frequency response tests, blade tap tests for delamination evaluation of composite components, ultrasonic inspection for delamination and internal damage of composite components, x-ray inspection for internal damage, and fluorescent penetrant inspection or magnetic particle inspection of metallic components.
4.6.5 Pass Fail Criteria.
Section 35.38 requires that a lightning strike on a “typical installation” does not cause a major or hazardous propeller effect. Composite propeller blades and associated airplane installation may have inherent mitigating features that would permit the release of debris due to lightning strike.
For twin-engine airplanes, the release of debris that would not have sufficient energy to penetrate a fuselage may be acceptable.
For nose mounted single engine tractor installations, propeller fragments caused by lightning strike would not hit the fuselage and cause damage to the airplane.
Therefore, the hazardous propeller effect is associated with unbalance loads.
Unbalanced loads that do not cause damage to the airplane or engine may be acceptable. When showing compliance with the lightning strike requirements of § 35.38, the FAA recommends the applicant identify the amount of blade loss, if any.
That information should be included in the installation manual provided to airframe manufacturers for aircraft testing.
4.7 Section 35.39, Endurance test.
4.7.1 Test Configuration.
Testing should be conducted with the propeller system. The engine power output should be at least equal to the propeller takeoff and maximum continuous power ratings. The rated rotational speed is typically the takeoff rotational speed. Spinner and de-ice components should be installed during the endurance test. However, in lieu of this for spinner and de-ice components, conducting a spin-rig test or similarity to a previously tested configuration may be acceptable.
4-5
4.7.2 Propeller Diameter.
When the propeller being certified includes more than one acceptable blade design, the diameter of the propeller tested need not be the blades that give maximum propeller diameter. The blades tested should be the ones for which certification is sought. The applicant should show that testing represents all other similar blades included in the type design. If the blades used during the endurance test differ from the blades being certified, the applicant should supply engineering data that shows the blades have similar loading and vibration characteristics and will have the same test results. In addition, testing with blades of different construction than blades for which certification is sought may not be acceptable, for example, if both composite and aluminum blade options are included in the type design, then both blades should be tested.
4.7.3 Representative Engine.
The representative engine must be capable of developing the power and speed for which certification of the propeller is sought. The engine vibration should be similar to the intended application for the propeller. For example, testing on a turbine engine to show that the propeller is acceptable on a piston engine may not be applicable.
4.7.4 Continuity of Test.
The endurance test may be continuous or incremental as agreed to by the applicant and Administrator.
4.7.5 Controls.
Controls must be operated according to the applicant’s instructions with minor alterations permitted by the Administrator. The applicant’s instructions should be proposed for incorporation into the propeller manuals.
4.7.6 Stops.
The endurance test should be run non-stop according to the approved test plan unless agreed to by the Administrator. In the event of a stop, that test period should be repeated unless the Administrator considers this unnecessary. The Administrator reserves the right to require the entire test be repeated, if an excessive number of stops occur.
4.8 Section 35.40, Functional test.
4.8.1 General Overview.
Functional tests are intended to substantiate the control function in the propeller system.
These tests can be performed in conjunction with §§ 35.39 and 35.42.
4.8.2 Governing Propellers.
The following simulated flight cycle examples may be used as representative flight cycles to demonstrate compliance to § 35.40(b):
Ground idle (GI) – stabilize.
4-6 Acceleration from GI to takeoff power – transition.
Takeoff power – stabilize.
Takeoff power to maximum continuous power – transition.
Maximum continuous power – stabilize.
Maximum continuous power to cruise power – transition.
Cruise power – stabilize.
Cruise power to descent power – transition.
Descent power – stabilize.
Descent power to GI – stabilize.
4.8.3 Feather Cycle.
The following feather cycle examples may be used to demonstrate compliance to § 35.40(c):
GI – stabilize.
GI to feather – transition.
Feather - stop rotation.
Unfeather to GI – transition.
4.8.4 Reverse Cycle.
The following reverse cycle examples may be used to demonstrate compliance to § 35.40(d):
GI – stabilize.
GI to maximum reverse power – transition.
Maximum reverse power – stabilize.
Maximum power to GI – transition.
The propeller or propeller control should not be altered to increase the envelope of the functional test cycle without concurrence of the Certificate Management Aircraft Certification Office. A non-feathering and non-reversing propeller will have a very limited pitch change range during this test, which is acceptable.
4.9 Section 35.41, Overspeed and overtorque.
Section 35.41 does not preclude the applicant from specifying (in the appropriate manuals) other overspeed and overtorque levels that would require maintenance actions, such as an overspeed level that would require the propeller to be removed and sent to a repair shop for inspection.
4-7 Maximum propeller overspeed would not require removal of the propeller for a service or maintenance action other than to correct the cause. This rotational overspeed should only be caused by an inadvertent service or maintenance action.
Maximum propeller overtorque would not require removal of the propeller for a service or maintenance action other than to correct the cause. This overtorque should only be caused by an inadvertent service or maintenance action.
4.10 Section 35.42, Components of the propeller control system.
Section 35.42 testing identifies the functionality and wear of the propeller pitch control system’s components for establishing the appropriate ICA. Tests should represent the hours of operation, which would arise within the initially declared overhaul period, but not less than the 1,000 hours of operation defined in the rule. Tests should explore all the operating conditions applicable to propeller components used in the control (including governors, pitch change assemblies, pitch locks, mechanical stops, feathering system components, beta control, and reverse thrust) of the propeller. Tests may be carried out on suitable rigs or in conjunction with the endurance and functional tests specified in §§ 35.39 and 35.40. Applicants must show compliance through tests, rational analysis based on test results, or service experience on similar components.
4.11 Section 35.43, Propeller hydraulic components.
Tests demonstrating the structural integrity of components should verify the structural adequacy of hydraulic components in the event of over pressurization of the system.
The burst pressure test should demonstrate structural integrity with no significant fracture. Verification that unacceptable permanent deformation did not take place may be shown by comparing dimensional part measurements before and after the test.
Advisory Circular Feedback Form If you find an error in this AC, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by (1) emailing this form to 9-AWA-AVS- AIR-DMO@faa.gov or (2) faxing it to (202) 267-1813.
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