(a) From minimum to rated takeoff power or thrust with the maximum bleed air and power extraction to be permitted in an aircraft, without overtemperature, surge, stall, or other detrimental factors occurring to the engine whenever the power control lever is moved from the minimum to the maximum position in not more than 1 second, except that the Administrator may allow additional time increments for different regimes of control operation requiring control scheduling; and
(b) From the fixed minimum flight idle power lever position when provided, of if not provided, from not more than 15 percent of the rated takeoff power or thrust available to 95 percent rated takeoff power or thrust in not over 5 seconds. The 5-second power or thrust response must occur from a stabilized static condition using only the bleed air and accessories loads necessary to run the engine. This takeoff rating is specified by the applicant and need not include thrust augmentation.
*** Guidance. The INTENT of this section is to assure that the engine is designed and fabricated with a minimum standard of power/thrust response characteristics.
Ineraft tune g}e, dated De and 131 Characteristics of References: None.
52. Section 33.75, Safety Analysis.
Section 33.75 Safety analysis.
It must be shown by analysis that any probable malfunction or any probable single or multiple failure, or any probable improper operation of the engine will not cause the engine to--
(a) Catch fire;
Burst (release hazardous fragments through the engine case);
specified in Section 33.23 (a); or Generate loads greater than those ultimate loads
(d) Lose the capability of being shut down.
*** Guidance. The INTENT of this section is to assure that the engine is designed and fabricated to preclude probable failure, malfunction, or operating conditions resulting in the hazards specified.
Chap 3 72 Par 51
Incorporations: None.
References: SAE ARP926A "Fault/Failure Analysis Procedure," levised November 15, 1979.
a. The safety analysis should support the engine design goals, such that there would not be a likely single tailure or failures that would result in fire, uncontained event, exceedance of engine ultimate loads, or prevent the engine from being shutdown.
b. The guidance provided in the reference above would be an acceptable methodology. The top-down technique is suggested based on the four critical failure modes identified in the rule. The analysis should cover:
(1) all major static and rotating components including mounts, seals, spacers, shafts, and bearings;
(2) all subsystems and components including fuel, lubrication, pneumatic, electronic, cooling, instrumentation, speed reduction, and fire protection.
c. A by-product of the safety analysis should be an assessment of all potentially hazardous conditions, individually and in combination including consideration of dormant failures, and the elimination of such conditions by redesign, required inspections, inspection intervals, specialized instrumentation, and/or finite lifing to support FAA findings of acceptable safety and durability levels.
53. Section 33.77, Foreign Object Ingestion.
Section 33.77 Foreign object ingestion.
(a) Ingestion of a 4-pound bird, under the conditions prescribed in paragraph (e) of this section, may not cause the engine to--
(1) Catch fire;
(2) Burst (release hazardous fragments through the engine case);
3) Generate loads qreater than those ultimate loads specified in Section 33.23(a); or
(4) Lose the capability of being shut down.
(b) Ingestion of 3-ounce birds or 1-1/2 pound birds, under the conditions prescribed in paragraph (e) of this section, may not-- Cause more than a sustained 25 percent power or thrust loss;
(2) Require the engine to be shut down within 5 minutes from time of ingestion; or
(3) Result in a potentially hazardous condition.
Chap 3 Par 52 73
(c) Ingestion of water, ice, or hail under the conditions prescribed in paragraph (e) of this section, may not cause a sustained power or thrust loss or require the engine to be shut down. It must be demonstrated that the engine can accelerate and decelerate safely while inducting a mixture of at least 4 percent water by weight of engine airflow following stabilized operation at both flight idle and takeoff power settings with at least a 4 percent water-to-air ratio.
(d) For an engine that incorporates a protection device, compliance with this section need not be demonstrated with respect to foreign objects to be ingested under the conditions prescribed in paragraph (e) of this section if it is shown that--
(1) Such foreign objects are a size that will not pass through the protective device;
(2) The protective device will withstand the impact of the foreign objects;
The foreign object, or objects, stopped by the protective device will not obstruct the flow of induction air into the engine with a resultant sustained reduction in power or thrust greater than those values required by paragraphs (b) and (c) of this section.
(e) Compliance with paragraphs (a), (b), and (c) of this section must be shown by engine test under the following ingestion conditions:
Foreign Test Quantity Speed of Foreign Object Engine Ingestion object Operation BIRDS:
3- One for each 50 square Liftoff speed of Takeoff.... In rapid sequence to ounce inches of inlet area or typical aircraft. simulate a flock Size.. fraction thereof up to a encounter and aimed maximum of 16 birds. Three- at selected critical once bird ingestion not areas.
required if a 1-1/2-pound bird will pass the inlet guide vanes into the rotor blades.
1-1/2- One for the first 300 square Initial climb speed of Takeoff........ In rapid sequence to pound inches of inlet area, it typical aircraft. simulate a flock size.. can enter the inlet, plus encounter and aimed one for each additional 600 at selected critical square inches of inlet area areas.
or fraction thereof up to a maximum of 8 birds.
Chap 3 74 Par 53
Foreign Test Quantity Speed of Foreign Object Engine Ingestion Object Operation 4- one, if it can enter the Maximum climb speed of Aimed at critical pound inlet. typical aircraft if the size.. engine has inlet guide vanes.
Liftoff speed of Takeoff. Aimed at critical typical aircraft, if area.
the engine does not have inlet guide vanes.
Ice. Maximum accumulation on a Sucked in Maximum To simulate a typical inlet cowl and cruise.. continuous maximum engine face resulting from a icing encounter at 2-minute delay in actuating 25 °F.
anti-icing system, or a slab of ice which is comparable in weight or thickness for that size engine.
HAIL: For all engines: With inlet Rough air flight speed Maximum cruise In a volley to
(0.8 to 0.9 area of not more than 100 of typical aircraft. at 15,000 feet simulate a hailstone specific square inches: one 1-inch altitude. encounter. One-half gravity) hailstone. the number of With inlet area of more than hailstones aimed at 100 square inches: one 1- random area over the inch and one 2-inch face of the inlet and hailstone for each 150 the other half aimed square inches of inlet area at the critical face or fraction thereof. area.
For supersonic engines (in Supersonic cruise Maximum Aimed at critical addition): 3 hailstones velocity. cruise... engine face area.
each having a diameter equal Alternatively, use to that in a straight line subsonic velocities variation from 1 inch at with larger hailstones 35,000 feet to 1/4 inch at to give equivalent 60,000 feet using diameter kinetic energy.
corresponding to the lowest supersonic cruise altitude expected.
water. At least 4 percent of engine Sucked in...... Flight idle, For 3 minutes each at airtlow by weight. acceleration, idle and takeoff, and takeoff, during acceleration deceleration. and deceleration in spray to simulate rain.
NOTE:--The term "inlet area" as used in this section means the engine inlet projected area at the front face of the engine. It includes the projected area of any spinner or bullet nose that is provided.
*** Guidance. The INTENT of this section is to assure that the engine is designed, fabricated, and tested to be structurally and operationally tolerant, to the degrees specified, following the specified ingestion events.
Chap 3 Par 53 75
Incorporations: AC 33-1B, 'Turbine Engine Foreign Object Ingestion and Rotor Blade Containment Type Certification Procedures, dated April 22, 1970.
References: None.
a. Previous to the Amendment 6 engine certification rules, the foreign object ingestion test requirements were generalized from Sections 33.13 and 33.19, Design Features and Durability, espectively. The incorporation above, and its earlier versions, in fact, provided the ingestion test requirements and procedures for the pre-Amendment 6 engines.
The certification rules subsequent to Amendment 5 are definitive. Although they have evolved to the current rules, the guidance embodied in the incorporation may be considered applicable, except where the AC conflicts with the rules. On this oasis, the incorporation, with regard to ingestion testing (not containment), coupled with Amendment 10's Section 33.77 Preamble, and the following clarifying information should be useful.
It has become clear, through recent certification programs of various engine manufacturers, that the medium bird ingestion test procedures are not being uniformly conducted. Specifically, variations have occurred in the length of time required before throttle adjustments are allowed following ingestion.
d. Paragraph 10b(1) (e) of the incorporation states, 'Duration of the engine running following ingestion of any Group II objects should be at least 5 minutes to determine whether the engine is in a condition of imminent failure but, in case of doubt as to actual engine condition or evident engine damage, longer post-ingestion test runs should be conducted.
Similarly, paragraph 1lb(2) states, #The engine is acceptable if tests demonstrate...its continued safe operation after the ingestion tests. There should be no indication of need for immediate shutdown or imminent failure during the ingestion tests.... Also, FAR Section 33.77 was recently revised (Amendment 33-10) to specify the 5-minute minimum running period from the time of ingestion. If an engine is allowed to be manually throttled-back (to just over 75 percent power) prior to 5 minutes following ingestion, some conditions of imminent failure, which may be present, are much less likely to be detected. Since one of the purposes of the ingestion test is to demonstrate the absence of imminent failure, manual intervention within 5 minutes should not be accepted.
A question concerning foreign object ingestion testing is, 'What is the definition of the term 'inlet area' as used in FAR Section 33.77, as applied to turbofan engines?" Amendment 10 Chap 3 76 Par 53
added the definition of this term at the end of the table in Section 33.77. For the typical turbotan engine, this is the bareengine inlet area calculated from De shown in Figure 1 (which follows paragraph 53j). Ds is the propulsion system feature that usually determines ingestion; that is, foreign object strikes outboard (relative to the duct centerline) of the highlight will usually be repelled, and strikes inboard of the highlight will usually be ingested. However, the nacelle design is not always known at time of engine certification testing and can change from one installation to another. Therefore, since De is a rough approximation of D for the typical turbofan engine, and since De is controlled by the engine manufacturer, it was chosen as the determinant of inlet area in the current rule.
Unfortunately, the definition in Amendment 33-12 is not without problems. For example, it is not clearly applicable to an aft-fan engine. Also, the nacelle inlet lip stagnation point area, As, (which as explained above, is the functional feature that normally determines ingestion, also known as the capture area) can be much larger than Ae, the bare-engine inlet area; and A is not particularly significant if the air inlet duct incorporates an inertial separator. Hence, judgement is required, and the following guidelines are recommended until a rule establishing an improved definition is promulgated.
Typical turbofan engines should use A, as defined herein and in Amendment 33-10 for calculating foreign object ingestion quantities. Other engines should use the capture area of the installed engine, if that area is known at the time of engine certification testing. If the nacelle design is not known, or if the manufacturer elects to do so, the engine inlet area, Ar historically. or estimated nacelle inlet, As, may be used, as has been done The TCDS or the FAA-approved engine installation manual (or similar document for non-domestic engines) should indicate which area was used for ingestion calculations. This area should be considered an installation limit. If a later engine installation results in a larger capture area, the foreign object ingestion test (quantities) should be re-evaluated for possible additional certification testing.
(3) In no case should the nacelle inlet throat area A{(f)D}, see Figure 1, be used for ingestion calculations as this may result in an invalid test.
h. The inlet area question is also most germane for the smaller mass-flow turboshaft (and some turboprop) engines. As in the turbofan engine case, the inlet area determinant for ingestion testing should be the free-stream capture area. This needs to be assumed as the front face area for the bare-engine case. If the engine design incorporates an inlet air separator system, then Chap 3 Par 53 77
engineering judgement will need to be applied to define the ingestion area for calculating ingestion quantities and for determining target areas.
i. The guiding principle should be the same in all cases; the induction air stream projected area exposed to the ingestion hazard should be the determinant area. This area must include the projected areas of spinners, inertial separator housings, starter housings, inlet nose cones, etc., if it is possible for the foreign object (s) to still be ingested after impacting such devices. One expected outcome of the ingestion test of such inlet configurations is to ensure that they are ingestion impact tolerant and do not, of themselves, become ingestion objects in the engine flow path.
j. The engine manufacturer may elect to require that the airframe manufacturer install the engine, such that it is impossible for free-stream ingestion objects to enter the engine inlet. In such a case, the TCDS and the installation instructions will need to specify this as an installations limitation. This approach has mostly been applied to rotorcraft engine installations wherein there is no direct line-of-sight between the ambient free-stream and the engine's front face. This arrangement effectively creates a zero ram-recovery plenum for the engine flow stream. The airframers would need to demonstrate that this produces no unairworthy or undesirable characteristic, in accordance with the certification rules for the installation.
Chap 3 78 Par 53
FIGURE 1. GENERIC TURBOFAN AND NACELLE CONFIGURATION Ds = nacelle inlet lip stagnation point equivalent diameter,
(a.k.a. highlight equivalent diameter).
D, = nacelle inlet throat equivalent diameter.
De = engine front face inlet equivalent diameter,
(a.k.a. bare-engine inlet equivalent diameter).
A = nD/¼, where n=pi.
Chap Par 53 . 79
54. Section 33.79, Fuel Burning Thrust Augmenter.
Section 33.79 Fuel burning thrust augmenter.
Each fuel burning thrust augmenter, including the nozzle, must--
(a) Provide cutoff of the fuel burning thrust augmenter:
(b) Permit on-off cycling;
Be controllable within the intended range of operation;
Upon a failure or malfunction of augmenter combustion, not cause the engine to lose thrust other than that provided by the augmenter; and
(e) Have controls that function compatibly with the other engine controls and automatically shut off augmenter fuel flow if the engine rotor speed drops below the minimum rotational speed at which the augmenter is intended to function.
*** Guidance. The INTENT of this section is to assure that the afterburner system is designed and constructed to function satisfactorily and not impair the functioning of the rest of the engine.
Incorporations: None.
References: None.
Chap 3 80 Par 54
SECTION 6. SUBPART F--BLOCK TESTS; TURBINE AIRCRAFT ENGINES
55. Section 33.82, General.
Section 33.82 General.
Before each endurance test required by this subpart, the adjustment setting and functioning characteristic of each component having an adjustment setting and a functioning characteristic that can be established independent of installation on the engine must be established and recorded.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
Collectively, the results of the block tests, combined with the design and analytical substantiation data, form the basis for the engine type certificate data sheet and engine instruction manuals statements concerning: ratings, steady-state and transient operating limits, critical parts retirement life, environmental envelope, inspection requirements, maintenance/overhaul requirements, operational requirements, and engine/airframe interface requirements.
56. Section 33.83, Vibration Test.
Section 33.83 Vibration test.
establish the vibration characteristics of the rotor Each engine must undergo a vibration survey to discs, rotor blades, rotor shafts, stator blades, and any other components that are subject to vibratory exciting forces which could induce failure at the maximum inlet distortion limit. The survey is to cover the range of rotor speeds and engine power or thrust, under steady state and transient conditions, from idling speed to 103 percent of the maximum permissible speed. The survey must be conducted using the same configuration of the loading device which is used for the endurance test, except that the Administrator may allow the use of a modified configuration if that loading device type is incompatible with the necessary vibration instrumentation.
(b) The vibration stresses (or strain) of rotor and stator components determined under paragraph (a) of this section must be less, by a margin acceptable to the Administrator, than the endurance limit of the material Chap 3 Par 55 81
from which these parts are made, adjusted for the most severe operating conditions.
Each accessory drive and mounting attachment must be loaded, with the load imposed by each accessory used only for an aircraft service being the limit load specified by the applicant for the engine drive or attachment point.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
a . The engine vibration survey should be conducted with a air distortion to be allowed by the engine installation distortion.
(1) The engine speed range to be surveyed is minimum idle speed to 103 percent of the maximum permissible speed.
maximum permissible speed is the highest rpm, including transients, for which the engine is to be approved.
(2) The principal result of the vibration survey is to demonstrate that an acceptable margin exists between the measured stresses and the endurance limit of the material being tested.
envelope of the engine, including the worst case inlet air distortion levels are found to be limiting, when correlated to ibratory stresses, then the engine installation instructions should specify those limits.
(3) Correspondingly, the recommended instrumentation, data acquisition and reduction methods, and coordination needs should also be provided in the engine installation instructions.
b. There are some engine designs which operate at such high rotor speeds and gas path temperatures that existing technology strain gages cannot survive this environment for very long. In such cases, the full stress survey should still be the goal and the test designed accordingly.
(1) If it becomes physically impossible to achieve the testing to 103 percent speed, then some form of analysis could be used to make up any difference.
Chap 3 82 Par 56
(2) Additionally, if any significant resonances are found in the operating range of the engine, then the engine should be run, at least, 10 million cycles at each resonant point and at points bracketing the resonances to assure the stress endurance limit is not exceeded. This is normally covered as part of the endurance test's incremental running.
57. Section 33.85, Calibration Tests.
Section 33.85 Calibration tests.
Each engine must be subjected to those calibration tests necessary to establish its power characteristics and the conditions for the endurance test specified in Section 33.87. The results of the power characteristics calibration tests form the basis for establishing the characteristics of the engine over its entire operating range of speeds, pressures, temperatures, and altitudes. Power ratings are based upon standard atmospheric conditions with no airbleed for aircraft services and with only those accessories installed which are essential for engine functioning.
accomplished on the endurance test engine after the endurance test and any change in power characteristics which occurs during the endurance test must be determined.
Measurements taken during the final portion of the endurance test may be used in showing compliance with the requirements of this paragraph.
*** Guidance. The INTENT of this section is to determine the engine power characteristics by test calibrating the engine either before and during, or after, the endurance test.
Incorporations: None.
References: None.
The engine calibration tests, in combination with the other block est requirements, form the basis for the engine instrumentation statements to be included in the engine installation instructions.
These statements should encompass types, ranges, precision (readability), and accuracies of those parameters required for safe in-service engine operation, including reverse thrust operations, for each of the ratings.
Chap 3 Par 56 83