SECTION 5. SUBPART E--DESIGN AND CONSTRUCTION; TURBINE AIRCRAFT ENGINES
42. Section 33.62, Stress Analysis.
Section 33.62 Stress analysis.
A stress analysis must be performed on each turbine engine showing the design safety margin of each turbine engine rotor, spacer, and rotor shaft.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
43. Section 33.63, Vibration.
Section 33.63 Vibration.
Each engine must be designed and constructed to function throughout its operating range of rotational speeds and engine power without inducing excessive stress in any engine part because of vibration and without imparting excessive vibration forces to the aircraft structure.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
44. Section 33.65, Surge and Stall Characteristics.
Section 33.65 Surge and stall characteristics.
When the engine is operated in accordance with operating instructions required by Section 33.5(b), starting, a change of power or thrust, power or thrust augmentation, limiting inlet air distortion, or inlet air temperature may not cause surge or stall to the extent that ilameout, structural failure, overtemperature, or failure of the engine to recover power or thrust will occur at any point in the operating envelope.
*** Chap 3 Par 42 63
Guidance. The INTENT of this section is to assure that the engine be designed and fabricated to preclude harmful surge and stall characteristics.
Incorporations: AC 33.65-1, ¿'¿Surge and Stall Characteristics of Aircraft Turbine Engines, dated December 1985.
References: None.
Note that this section addresses design and construction requirements; correlating block test requirements are prescribed in "Section 33.89, Operation Test".
45. Section 33.66, Bleed Air System.
Section 33.66 Bleed air system.
The engine must supply bleed air without adverse effect on the engine, excluding reduced thrust or power output, at all conditions up to the discharge flow conditions established as a limitation under Section
33.7(c) (11). If bleed air used for engine anti-icing can be controlled, provision must be made for a means to indicate the functioning of the engine ice protection system.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
The need to restrict bleed airflow, such as by orifice(s), should either be incorporated in the type design of the engine hardware, or be noted as appropriate in the engine installation instructions (and drawings) and in the engine type certificate data sheet (TCDS) .
46. Section 33.67, Fuel System.
Section 33.67 Fuel system.
(a) With fuel supplied to the engine at the flow and pressure specified by the applicant, the engine must function properly under each operating condition required by this Part. Each fuel control adjusting means that may not be manipulated while the fuel control device is mounted on the engine must be secured by a locking device and sealed, or otherwise be inaccessible. All other fuel control adjusting means must be accessible and marked to Chap 3 64 Par 44
indicate the functioning of the adjustment unless the function is obvious.
(b) There must be a fuel strainer or filter between the engine fuel inlet opening and the inlet of either the fuel metering device or the engine-driven positive displacement pump whichever is nearer the engine fuel In addition, the following provisions apply to each strainer or filter required by this paragraph.
It must be accessible for draining and cleaning and must incorporate a screen or element that is easily removable.
(2) It must have a sediment trap and drain except that it need not have a drain if the strainer or filter is easily removable for drain purposes.
(3) It must be mounted so that its weight is not supported by the connecting lines or by the inlet or outlet connections of the strainer or filter, unless adequate strength margins under all loading conditions are provided in the lines and connections.
(4) It must have the type and degree of fuel filtering specified as necessary for protection of the engine fuel system against foreign particles in the fuel.
The applicant must show:
(i) That foreign particles passing through the specified filtering means do not impair the engine fuel system functioning; and
(ii) That the fuel system is capable of sustained operation throughout its flow and pressure range with the fuel initially saturated with water at 80 degrees F (27 °C) and having 0.025 fluid ounces per gallon (0.20 milliliters per liter) of free water added and cooled to the most critical condition for icing likely to be encountered in operation. However, this requirement may be met by demonstrating the effectiveness of specified approval fuel anti-icing additives, or that the fuel system incorporates a fuel heater which maintains the fuel temperature fuel strainer or fuel inlet above 32 degrees F (0 °C) under the most critical conditions.
(5) The applicant must demonstrate that the filtering means has the capacity (with respect to engine operating limitations) to ensure that the engine will continue to operate within approved limits, with fuel contaminated to the maximum degree of particle size and density likely to be encountered in service. Operation under these conditions must be demonstrated for a period acceptable to the Administrator, beginning when indication of impending filter blockage is first given by either:
1) Existing engine instrumentation; or
(ii) Additional means incorporated into the engine fuel system.
(6) Any strainer or filter bypass must be designed and constructed so that the release of collected Chap 3 Par 46 65
contaminants is minimized by appropriate location of the bypass to ensure that collected contaminants are not in the bypass flow path.
(c) If provided as part of the engine, the applicant must show for each fluid injection (other than fuel) system and its controls that the flow of the injected fluid is adequately controlled.
*** Guidance. The INTENT of this section is to assure that the engine fuel system is designed and fabricated to operate satisfactorily under all applicable operating conditions.
Incorporations: None.
References: Military Specification MIL-E-5007E(AS), "Engines, Aircraft, Turbojet and Turbofan, General Specification For," dated September 1, 1983.
can be satisfactorily, for at least one half of flight time (of the intended aircraft applications), beginning at first indication of impending filter blockage. Actual, or rigsimulation of, test engine operation should be at the most critical mission fuel flows expected to be used in service.
Table X of the reference provides an example of typical fuel contaminants, particle sizes, and quantities.
47 • Section 33.68, Induction System Icing.
Section 33.68 Induction system icing.
Each engine, with all icing protection systems operating, must--
(a) Operate throughout its flight power range (including idling) without the accumulation of ice on the engine components that adversely affects engine operation or that causes a serious loss of power or thrust in continuous maximum and intermittent maximum icing conditions as defined in Appendix C of Part 25 of this chapter; and Idle for 30 minutes on the ground, with the available air bleed for icing protection at its critical condition, without adverse effect, in an atmosphere that is at a temperature between 15 degrees and 30 degrees F (between -9 degrees and -1 degrees C) and has a liquid water content not less than 0.3 grams per cubic meter in the form of drops having a mean effective diameter not less than 20 microns, followed by a momentary operation at Chap 3 66 Par 46
takeoff power or thrust. During the 30 minutes of idle operation the engine may be run up periodically to a moderate power or thrust setting in a manner acceptable to the Administrator.
*** Guidance. The INTENT of this section is to assure that the engine induction icing protection system be designed and fabricated to operate satisfactorily during the icing conditions specified.
Incorporations: AC 20-73, "Aircraft Ice Protection," dated April 21, 1971.
References: None.
a . Certification of engine icing protection systems is conducted to the criteria of continuous icing. That is, engine certification for induction system icing does not recognize timelimited approvals for inadvertent icing encounters.
b. There may be instances where the engine manufacturer elects to design an aircraft induction system as part of the engine bill-of-material and then perform icing analyses and tests of the complete engine/aircraft induction system configuration.
This, of course, "locks in" the induction system design, as part of the engine type design for all future applications of the engine. Subsequent deviations from this approved design configuration would invalidate the engine's anti-icing approval and, therefore, would violate the type certificate limitations of the engine.
The guidance material for icing protection of engines embodied in AC 20-73, dated April 21, 1971, is still considered valid and useful. In particular, the "two point" test method (Icing Conditions 1 and 2 in the Table of Paragraph 33b(2)) is considered adequate substantiation--when supported by design analysis of the critical conditions for icing protection.
d. The analysis should consider, in part:
1) for engine bleed air systems, the requirements and limitations of the bleed air characteristic.
(2) the corresponding need to establish operating limitations (and/or minimums) of rotational speed, power or thrust, etc., to maintain the minimum required anti-icing bleed air characteristic.
(3) the affect of ice accretion on engine instrumentation probes or sensors located in the induction air stream.
Chap 3 Par 47 67
(4) the maximum customer bleed air extraction on engines which utilize bleed air anti-ice systems.
e. The third test point of the Icing Conditions Table of Paragraph 33b(2) of AC 20-73 refers to the ground fog icing condition. Note that it has been modified by Amendment 10 of Part 30, According count the tablete that me nament io 30", and "≥ 20" permits periodic engine accelerations during the idle icing condition of Section 33.68 (b) to shed ice build-ups.
The icing test periods of 10 and 30 minutes suggested in the AC, Paragraphs 33b(2) (a) and (b) respectively, should be understood to be minimum test times. Nonstabilized engine operation, or continued ice build-up at the conclusion of the test period, would be cause to extend the basic 10 or 30 minute test period. Testing should continue until an ice build-up and shed cycle is established, or until engine operation is stabilized, or until the engine will no longer safely operate within limits.
g. Normal engine parameters of EPR, torque, high pressure rotor speed, low pressure rotor speed, gas path temperature, and fuel flow should be monitored to verify stability of engine operation during the icing test. Closed circuit television monitoring of the critical areas during the test is a useful method to verify the icing characteristics and ice build/shed cycle. Post test point icing characteristics are also typically documented by photographic means, immediately following engine shutdown after each test point of interest.
h. The characteristics and calibration of the icing test facility should be documented to substantiate proper liquid water content (LWC), dropiet diameter, and atmospheric temperature.
Note that anti-icing certification of engines to FAR Part 33 does not include snow ingestion testing. The snow ingestion test requirements of subsection .1093(b) (ii) of FAR Parts 23, 25, 27, and 29 cannot be included in Part 33 since the principal purpose of snow testing is to evaluate the complete engine installation within the airplane or rotorcraft environment. For rotorcraft installations, this includes evaluation of the influences of engine inlet duct geometry and placement, bypass ratio, rotor-wash effects, etc., which are impossible to evaluate at the bare engine level.
48. Section 33.69, Ignition System.
Section 33.69 Ignition system.
Each engine must be equipped with an ignition system for starting the engine on the ground and in ilight.
electric ignition system must have at least two igniters Chap 3 68 Far 47
and two separate secondary electric circuits, except that only one igniter is required for fuel burning augmentation systems.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
The engine installation instructions should define the characteristics and the interface requirements of all aircraft sources of electrical power required by the engine ignition system.
49. Section 33.71, Lubrication System.
Section 33.71 Lubrication system.
(a) General. Each lubrication system must function properly in the flight attitudes and atmospheric conditions in which an aircraft is expected to operate.
(b) Oil strainer or filter. There must be an oil strainer or filter through which all of the engine oil In addition:
(1) Each strainer or filter required by this paragraph that has a bypass must be constructed and installed so that oil will flow at the normal rate through the rest of the system with the strainer or filter element completely blocked.
The type and degree of filtering necessary for protection of the engine oil system against foreign particles in the oil must be specified. The applicant must demonstrate that foreign particles passing through the specified filtering means do not impair engine oil system functioning.
Each strainer or filter required by this paragraph must have the capacity (with respect to operating limitations established for the engine) to ensure that engine oil system functioning is not impaired with the oil contaminated to a degree (with respect to particle size and density) that is greater than that established for the engine in subparagraph (2) of this paragraph.
(4) For each strainer or filter required by this paragraph, except the strainer or filter at the oil tank outlet, there must be means to indicate contamination before it reaches the capacity established in accordance with paragraph (b) (3) of this section.
Chap 3 Par 48 69
(5) Any filter bypass must be designed and constructed so that the release of collected contaminants is minimized by appropriate location of the bypass to ensure that the collected contaminants are not in the bypass flow path.
(6) Each strainer or filter required by this paragraph that has no bypass, except the strainer or filter at an oil tank outlet or for a scavenge pump, must have provisions for connection with a warning means warn the pilot of the occurrence of contamination of the screen before it reaches the capacity established in accordance with subparagraph (3) of this paragraph.
(7) Each strainer or filter required by this paragraph must be accessible for draining and cleaning.
(c) Oil tanks.
Each oil tank must have an expansion space of not less than 10 percent of the tank capacity.
. It must be impossible to inadvertently fill the oil tank expansion space.
(3) Each recessed oil tank filler connection that can retain any appreciable quantity of oil must have provision for fitting a drain.
Each oil tank cap must provide an oil-tight seal.
Each oil tank filler must be marked with the word "oil."
(6) Each oil tank must be vented from the top part of the expansion space, with the vent so arranged that condensed water vapor that might freeze and obstruct the line cannot accumulate at any point.
(7) There must be means to prevent entrance into the oil tank or into any oil tank outlet, of any object that might obstruct the flow of oil through the system.
(8) There must be a shutoff valve at the outlet of each oil tank, unless the external portion of the oil system (including oil tank supports) is fireproof.
Each unpressurized oil tank may not leak when subjected to maximum operating temperature and an internal pressure of 5 p.s.i., and each pressurized oil tank may not leak when subjected to maximum operating temperature and internal pressure that is not less than 5 p.s.i. plus the maximum operating pressure of the tank.
(10) Leaked or spilled oil may not accumulate between the tank and the remainder of the engine.
(11) Each oil tank must have an oil quantity indicator or provisions for one.
If the propeller feathering system depends or engine oil--
(i) There must be means to trap an amount of oil in the tank if the supply becomes depleted due to failure of any part of the lubricating system other than the tank itself;
Chap 3 70 Par 49
(ii) The amount of trapped oil must be enough to accomplish the feathering operation and must be available only to the feathering pump; and Provision must be made to prevent sludge or other foreign matter from affecting the safe operation of the propeller feathering system.
(d) Oil drains. A drain (or drains) must be provided to allow safe drainage of the oil system. Each drain must--
(1) Be accessible; and
(2) Have manual or automatic means for positive locking in the closed position.
Oil radiators. Each oil radiator must withstand, without failure, any vibration, inertia, and oil pressure load to which it is subjected during the block tests.
*** Guidance. The INTENT of this section is to assure that the engine lubrication system is designed and constructed to operate satisfactorily under all applicable operating conditions.
Incorporations: None.
References: None.
50. Section 33.72, Hydraulic Actuating Systems.
Section 33.72 Hydraulic actuating systems.
Each hydraulic actuating system must function properly under all conditions in which the engine is expected to operate. Each filter or screen must be accessible for servicing and each tank must meet the design criteria of Section 33.71.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
51. Section 33.73, Power or Thrust Response.
Section 33.73 Power or thrust response.
The design and construction of the engine must enable an increase-- Chap 3 Par 49 71
(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