(a)(3) (ii) and (iii) of this section may be accomplished through appropriate analytical means.
(b) The operation test must include all testinq found necessary by the Administrator to demonstrate that the engine has safe operating characteristics throughout its specified operating envelope.
Guidance. The INTENT of this section is to demonstrate safe operating characteristics and a minimum standard of power/thrust response characteristics.
Incorporations: AC 33.65-1, "Surge and Stall Characteristics of Aircraft Turbine Engines," dated December 6, 1985.
References: None.
Note: Although the incorporation applies to large high bypass ratio turbofan engines, the guidance material therein may also be useful for other engine applications.
This section addresses the block test requirements covering surge and stall characteristics. The correlating design and construction requirements are addressed in Section 33.65, "Surge and stall characteristics."
b. Engine transient characteristics at altitude should be defined by testing. However, steady state testing in an altitude test facility, in addition to component and engine analysis, is acceptable, when facility limitations preclude altitude transient testing, if accomplished as follows:
(1) Qualitatively determine, by sea level testing, the transient operating characteristics, including acceleration, deceleration, surge, stall, and flameout.
(2) Considering the limitations of the available altitude test facility, perform a quantitative analysis of the operating characteristics, identified by the above testing, over the complete operating range of the engine.
(3) Select, on the basis of the analysis, those critical conditions which may provide a problem in projected aircraft usage; and demonstrate quantitatively, on a quasi-steady basis, the validity of the analysis in the altitude test facility.
"Quasi-steady" means that disturbances of short duration will be applied to the engine when operating on the steady-state operating line, such that the effect of the transient on the engine is determined before the test facility conditions are disturbed.
Chap 3 94 Par 60
(4) As a part of the sea level demonstration, the ability of the engine to withstand takeoff surge, without damage, should be shown.
(5) The testing and analysis should show that margins are adequate to tolerate likely variations in fuel schedule, variable geometry schedule, anticipated installations and environmental (temperature, pressure, humidity) effects.
C. The operation test should also include:
(1) Low temperature and high temperature tests (fluids and carcass) for starting and operating the engine.
(2) Substantiation of the ignition system design duty cycle.
(3) Substantiation of the propeller parking brake, if the engine is so equipped.
(4) Substantiation of the engine ground and, where feasible, the in-flight starting envelopes. This substantiation should address all possible combinations of ignition system operation and power sources to be approved, and should result in defined acceptable start times, from initiation of the starting sequence to stabilized idle conditions.
(5) Substantiation of the propeller parking brake, if the engine is so equipped.
(6) Substantiation of all engine operating attitudes, and additionally, for powered-lift engines rotationally displaceable along their longitudinal axis, slue angles, and rates.
61. Section 33.90, Initial Maintenance Inspection.
Section 33.90 Initial maintenance inspection.
Each engine, except engines being type certificated through amendment of an existing type certificate or through supplemental type certification procedures, must undergo an approved test run that simulates the conditions in which the engine is expected to operate in service, including start-stop cycles, to establish when the initial maintenance inspection is required. The test run must be accomplished on an engine which substantially conforms to the final type design.
*** Guidance. The INTENT of this section is to demonstrate the ability of new type certificate engines to operate in a simulation Chap 3 Par 60 95
of expected service conditions, for a specified number of cycles and/or hours before requiring maintenance inspection.
Incorporations: None.
References: None.
The requirements of this section are separate and distinct from those of Section 33.14, "Start-stop cyclic stress."
up mental test fat Age leant my sundat as from development tests and service experience where applicable and when creditable. The following information should be supplied to permit assessment of the inspection/overhaul period in support of the abbreviated flight cycle:
(1) The design flight cycle for the engine should identity the time history of engine power, or thrust usage including reverse thrust, if applicable, from engine start-up through shutdown, during a typical flight of a representative aircraft which uses the engine.
(2) The design analysis should identify those features of the engine for which initial life limitations will be established, or which will require threshold maintenance inspection; and whether a limitation is based on low cycle fatigue (cycles) or total engine or part-time (hours).
(3) A substantiation of the validity of the limitations and the acceptability of the test procedure as a valid representation of the design flight cycle, with regard to stress, temperature, and vibration (simulating the maximum rotor imbalances to be approved for production acceptance).
b. The initial maintenance inspection test run of engines designed to drive a propeller should be equipped with a propeller representative of the intended application, and include propeller parking brake usage and APU-mode operations, if so equipped.
62. Section 33.91, Engine Component Tests.
Section 33.91 Engine component tests.
(a) For those systems that cannot be adequately substantiated by endurance testing in accordance with the provisions of Section 33.87, additional tests must be made to establish that components are able to function reliably in all normally anticipated flight and atmospheric conditions.
Chap 3 96 Par 61
(b) Temperature limits must be established for those components that require temperature controlling provisions in the aircraft installation to assure satisfactory functioning, reliability, and durability.
Each unpressurized hydraulic fluid tank may not fail or leak when subjected to maximum operating temperature and an internal pressure of 5 p.s.i.' leak when pressurized hydraulic fluid tank may not fail or subjected to maximum operating temperature and an internal pressure not less than 5 p.s.i. plus the maximum operating pressure of the tank.
For an engine type certificated for use in supersonic aircraft, the systems, safety devices, and petite and test that may fail because of operation at maximum and minimum operating temperatures must be identified and tested at maximum and minimum operating temperatures and while temperature and other operating conditions are cycled between maximum and minimum operating values.
*** Guidance. The INTENT of this section is to assure test substantiation of all engine components, functions, and features which would not otherwise have been evaluated by endurance or other testing.
Incorporations: None.
References: None.
Engine component tests may include, but are not limited to, the following:
Fire proof/resistance tests of flammable fluid carrying or holding components.
b. Sea level and altitude pressure conditions testing/calibration of electronic control, fuel, lube, pneumatic, and starting systems.
c. Cold and hot ambient temperature conditions testing/calibration of fuel, lube, pneumatic, and starting systems.
d. Other environmental testing, such as salt spray, humidity, fungus, explosive atmosphere, etc.
e. Electromagnetic compatibility (EMC/HERF) testing.
f. Testing of engine electronic control lightning tolerance, as discussed under Section 33.7 of this AC.
Chap 3 Par 62 97
g. Engine thrust reverser systems tests.
h. Engine mount structure loads tests.
i. Engine ignition systems (duty cycles) tests.
j. Compressor mapping tests.
K. Engine control and monitoring systems software validations; and
1. Tests of electronic control integrity, while operating with various combinations of intended dispatchable control subsystem failures.
63. Section 33.92, Windmilling Tests.
Section 33.92 Windmilling tests.
(a) For engines to be used in supersonic aircraft, unless means are incorporated in the engine to stop rotation of the engine rotors when the engine is shut down in flight, each engine rotor must either seize or be capable of rotation for 3 hours at the limiting windmilling rotational r.p.m. with no oil in the engine system, without the engine--
(1) Catching fire;
(2) Bursting (releasing hazardous uncontained fragments) ; or
(3) Generating loads greater than those ultimate loads specified in Section 33.23(a).
(b) A turbojet or turbofan engine incorporating means to stop rotation of the engine rotors when the engine is shut down in flight must be subjected to 25 operations under the following conditions:
(1) Each engine must be shut down while operating at rated maximum continuous thrust.
(2) For engines certificated for use on supersonic aircraft, the temperature of the induction air and the external surfaces of the engine must be held at the maximum limit during the tests required by this paragraph.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
Chap 3 98 Par 62
The FAA dropped the pre-Amendment 10 requirement for windmilling tests of subsonic turbine engines, on the basis that it imposed an unnecessary burden on the engine manufacturer, and that service experience showed no reported incidents involving windmilling hazards resulting from loss of engine oil.
64. Section 33.93, Teardown Inspection.
Section 33.93 Teardown inspection.
After completing the endurance test, each engine must be completely disassembled, and--
(a) Each component having an adjustment setting and a functioning characteristic that can be established independent of installation on the engine must retain each setting and functioning characteristic within the limits that were established and recorded at the beginning of the test; and
(b) Each engine part must conform to the type design and be eligible for incorporation into an engine for continued operation, in accordance with information submitted in compliance with Section 33.4.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
65. Section 33.94, Blade Containment and Rotor Unbalance Tests.
Section 33.94 Blade containment and rotor unbalance tests.
(a) Except as provided in paragraph (b) of this section, it must be demonstrated by engine tests that the engine is capable of containing damage without catching fire and without failure of its mounting attachments when operated for at least 15 seconds, unless the resulting engine damage induces a self shutdown, after each of the following events:
Failure of the most critical compressor or fan blade while operating at maximum permissible r.p.m. The blade failure must occur at the outermost retention groove or, for integrally-bladed rotor discs, at least 80 percent of the blade must fail.
2) Failure of the most critical turbine blade while operating at maximum permissible r.p.m. The blade failure must occur at the outermost retention groove or, for integrally-bladed rotor discs, at least 80 percent of the blade must fail. The most critical turbine blade must be Chap 3 Par 63 99
determined by considering turbine blade weight and the strength of the adjacent turbine case at case temperatures and pressures associated with operation at maximum permissible r.p.m.
Analysis based on rig testing, component testing, or service experience may be substituted for one of the engine tests prescribed in paragraphs (a) (1) and (a) (2) of this section if--
(1) That test, of the two prescribed, produces the least rotor unbalance; and
(2) The analysis is shown to be equivalent to the test.
*** Guidance. The INTENT of this section is to demonstrate engine blade containment by test, or by test and, in part, by proven analytical methodology.
Incorporations: AC 33-5, 'Turbine Engine Rotor Blade Containment Durability, dated November 7, 1989.
References: None.
66. Section 33.95, Engine-propeller Systems Tests.
Section 33.95 Engine-propeller systems tests.
engine is designed to operate with a propeller, the following tests must be made with a representative propeller installed by either including the tests in the endurance run or otherwise performing them in a manner acceptable to the Administrator:
Feathering operation: 25 cycles.
Negative torque and thrust system operation: 25 cycles from rated maximum continuous power.
(c) Automatic decoupler operation: 25 cycles from rated maximum continuous power (if repeated decoupling and recoupling in service is the intended function of the
(d) Reverse thrust operation: 175 cycles from the flight idle position to full reverse and 25 cycles at rated maximum continuous power from full forward to full reverse thrust. At the end of each cycle the propeller must be operated in reverse pitch for a period of 30 seconds at the maximum rotational speed and power specified by the applicant for reverse pitch operation.
*** Chap 3 100 Par 65
Guidance. The INTENT of this section is to assure that the engine, if designed to operate with a propeller, has been minimally tested with a representative propeller installed.
Incorporations: None.
References: None.
67 . Section 33.96, Engine Tests in Auxiliary Power Unit (APU) Mode.
Section 33.96 Engine tests in auxiliary power unit (APU) mode.
If the engine is designed with a propeller brake which will allow the propeller to be brought to a stop while the gas generator portion of the engine remains in operation, and remain stopped during operation of the engine as an auxiliary power unit ("APU mode"), in addition to the requirements of Section 33.87, the applicant must conduct the following tests:
(a) Ground locking: A total of 45 hours with the propeller brake engaged in a manner which clearly demonstrates its ability to function without adverse effects on the complete engine while the engine is operating in the APU mode under the maximum conditions of enqine speed, torque, temperature, air bleed, and power extraction as speciiied by the applicant.
(b) Dynamic braking: A total of 400 applicationrelease cycles of brake engagements must be made in a manner which clearly demonstrates its ability to function without adverse effects on the complete engine under the maximum conditions of engine acceleration/deceleration cate, speed, torque, and temperature as specified by the applicant. The propeller must be stopped prior to brake release.
(C) One hundred engine starts and stops with the propeller brake engaged.
(d) The tests required by paragraphs (a), (b), and
(c) of this section must be performed on the same engine used for the tests required by Section 33.87.
(e) The tests required by paragraphs (a), (b), and
(c) of this section must be followed by engine disassembly to the extent necessary to show compliance with the requirements of Section 33.93(a) and Section 33.93(b).
*** Guidance. The INTENT of this section is to assure that turboprop engines incorporating propeller brake (APU-mode) features are tested to ensure compatibility of those features with the rest of the engine.
Chap 3 rar 66 101
Incorporations: None.
References: None.
a. These tests are intended to provide for the assessment of:
(1) Hot section tolerance for locked rotor operations effects on combustor stability/coking, turbine nozzle integrity, turbine blade integrity, vibration, etc.; and
(2) Engine drive system stability/response, including the power turbine rotors, shafting, bearings and supports, reduction and accessory gear trains, and rotor brake components.
b. These propeller brake tests may be conducted in conjunction with the required tests of Section 33.87, where conditions permit, and if found appropriate by the Administrator.
c. The existing airworthiness standards concerning engine installations in FAR Parts 23 and 25, are considered adequate to assure a minimum level of airworthiness for certification installations of engines designed with propeller brakes for APU mode operations.
(1) In this case, the engine manufacturer will be the engine in scordance withe mode required to perform a safety analysis, in accordance with the existing requirements of Section 33.75, which addresses APU mode operations.
(2) It is intended that the results of this analysis be applied, as necessary, to the installed engine safety analysis, at the airframe level by the airframe manufacturer, to demonstrate compliance with Sections 23.1309 or 25.1309, as appropriate.
68. Section 33.97, Thrust Reversers.
Section 33.97 Thrust reversers.
(a) If the engine incorporates a reverser, the endurance, calibration, operation, and vibration tests prescribed in this subpart must be run with the reverser installed. In complying with this section, the power control lever must be moved from one extreme position to the other in not more than 1 second except, ii regimes oi control operations are incorporated necessitatino scheduling of the power-control lever motion in going from one extreme position to the other, a longer period of time is acceptable but not more than 3 seconds. In addition, the test prescribed in paragraph (b) must be made. This test may be scheduled as part of the endurance run.
Chap 3 102 Par 67
one hundred seventy-five reversals must be made from flight-idle forward thrust to maximum reverse thrust and 25 reversals must be made from rated takeoff thrust to maximum reverse thrust. After each reversal, the reverser must be operated at full reverse thrust for a period of 1 minute, except, that, in the case of a revèrser intended for use only as a braking means on the ground, the reverser need only be operated at full reverse thrust for 30 seconds.
*** Guidance. The INTENT of this section is to assure that engines incorporating thrust reversers are tested to ensure reverser airworthiness and compatibility with the rest of the engine.
Incorporations: AC 20-18A 'Qualification Testing of Turbojet Engine Thrust Reversers," dated March 16, 1966.
References: None.
Note that the published volume of the Code of Federal Regulations, Aeronautics and Space Title 14, Parts 1 to 59, has an omission in Section 33.97. This publication omits the comma in Section
33.97(a) following "endurance". Thus, some interpretations have been made that an endurance test with the reverser installed is not required; but rather a calibration test as that associated with pre- and post-endurance testing is the requirement (in addition to operation and vibration tests). The point of clarification herein is that an endurance test, a calibration test, an operation test, and a vibration test are all required to evaluate thrust reversers.
69. Section 33.99, General Conduct of Block Tests.
Section 33.99 General conduct of block tests.
Each applicant may, in making a block test, use separate engines of identical design and construction in the vibration, calibration, endurance, and operatior tests, except that, if a separate engine is used for the endurance test it must be subjected to a calibration check before starting the endurance test.
(b) Each applicant may service and make minor repairs to the engine during the block tests in accordance with the service and maintenance instructions submitted in compliance with Section 33.4. If the frequency of the service is excessive, or the number of stops due to engine malfunction is excessive, or a major repair, or replaccemenntf a part is found necessary during the block tests or as the result of findings from the teardown chap 3 Par 68 103
inspection, the engine or its parts must be subjected to any additional tests the Administrator finds necessary.
Each applicant must furnish all testing facilities, including equipment and competent personnel, to conduct the block tests.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
70. Section 33.13, Design Features.
Section 33.13 Design features.
The engine may not have design features that experience has shown to be hazardous or unreliable.
suitability of each questionable design detail or part must be established by tests.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
This rule applies to engines having a type certification basis of FAR Part 33, Amendment 5, or earlier. This rule was deleted by Amendment 6 on the basis that the regulations contain adequate and appropriate safety standards for aircraft engines. The preamble for the deletion further stated that testing of questionable design features may be required under the provisions of section
21.33 and special conditions may be prescribed under Section 21.16 for novel or unusual design features.
Chap 3 104 Par 69
Appendix 1 APPENDIX 1. TURBINE ENGINE MODEL DESCRIPTION PURPOSE • This appendix outlines the turbine engine model descriptive information that should be submitted in order to establish those features of the engine that are involved in the certification and safe operation of the engine.
DISCUSSION. The applicant should submit, where applicable, the following information, plus any additional information which, in the applicant's opinion, is essential to the certification and
a. Applicant's name.
b. Engine model, type, number of rotors, stages and their arrangement.
C • Performance ratings as defined in FAR Part 1 (See Table 1 of this appendix).
d. Performance charts consistent with the ratings.
Maximum structural loading envelope, including mounting attachments and allowable loads.
Maximum time the engine may be operated under negative and zero "g" conditions.
Maximum permissible temperature limits and cooling criteria for engine components and accessories.
(1) Type and location of thermocouple to use for cooling test, as applicable.
(2) Description of temperature sensing provisions, if incorporated.
h. Bleed air characteristic including temperature, pressure, and flow limits, and the extent and nature of contaminants that may be present and possibly harmful, if breathed.
i. Maximum permissible air inlet duct attachment loads.
(1) Shear loads.
(2) Loads normal to mounting surfaces.
(3) Overhang moment.
Par 1 1