of each test run should be one-third of the time specified in that section; however, the time may be varied to meet special conditions. The vibration, calibration and detonation tests prescribed in §§ 13.151 through 13.153 should be conducted during this test.

(b) The flight portion of the test should be conducted under normal operating conditions for 200 hours on an experimental (NX) basis. The spark plugs should be inspected in accordance with paragraph (c) (3) of this section at 30- to 50-hour intervals.

(2) Spark plugs of a design similar to an approved type. The manufacturer of a spark plug that is approved for a lower rated engine of a series of engines may modify the basic spark plug by changing its characteristics to accommodate the higher IMEP of other engines of the same series with higher hp ratings. The modified spark plugs will be granted approval for use with all engines of the particular model involved upon satisfactory completion of either of the procedures in subparagraph (1) of this paragraph or the following ground and flight service test:

(i) Ground test. A 50-hour engine block test should be conducted in accordance with the requirements

of

§ 13.154. The total time of each test run should be one-third of the time specified in that section; however, the time may be varied to meet special conditions. The vibration, calibration and detonation tests prescribed in §§ 13.151 through 13.153 should be conducted during this test. Upon satisfactory completion of this test, approval will be granted for limited use of the spark plug in aircraft for the purpose of flight service testing in not more than two aircraft as follows:

(ii) Flight service test. (a) When installed in engines of aircraft being operated under Parts 40, 41 or 42 of this subchapter, 250 hours of flight under normal operating conditions should be conducted and the spark plugs inspected in accordance with paragraph (c) (3) of this section at 30- to 50-hour intervals.

(b) When installed in engines of aircraft being operated under Part 43 of this subchapter, 100 hours of flight under normal operating conditions should be conducted and the spark plugs inspected in accordance with paragraph (c) (3) of this section at 20- to 25-hour intervals.

(f) Spark plugs for obsolescent engines (1) Spark plugs of a new design or of a type that has been approved for use with other engine models. The test procedures outlined in paragraph (e) (1) of this section apply.

(2) Spark plugs of a design similar to an approved type. It sometimes happens that the spark plug manufacturer may wish to tailor or redesign a type of spark plug previously approved for use in certain engines in order that the redesigned spark plug will be suitable for use in an obsolescent engine of a different series of engines. Upon satisfactory completion of the block test and the applicable flight service test specified below the redesigned spark plug will be granted approval for use in all engines of the particular model involved.

(i) Block test. This test should be conducted using the procedure of para- | graph (e) (2) (i) of this section. Upon satisfactory completion of this block test approval will be granted for limited use of the spark plug in aircraft for the purpose of flight service testing in not more than two aircraft as follows:

(ii) Flight service test. (a) When installed in engines of aircraft being operated under Parts 40, 41 or 42 of this subchapter, 150 hours of flight under normal operating conditions should be conducted and the spark plugs inspected in accordance with paragraph (c) (3) of this section at 25- to 30-hour intervals.

(b) When installed in engines of aircraft being operated under Part 43 of this subchapter, 50 hours of flight under normal operating conditions should be conducted and the spark plugs inspected in accordance with paragraph (c) (3) of this section at 10- to 15-hour intervals.

(g) Spark plugs for obsolete 150-hour engines (1) Spark plugs of new design. The test procedures outlined in paragraph (e) (1) of this section apply.

(2) Spark plugs of a design similar to an approved type. Upon satisfactory completion of the preignition test and the applicable flight service test specified below, spark plugs of a type, or similar to a type which has been previously approved for use in one or more specific engine models, will be granted approval for use with all obsolete engine models for which the approved spark plug used in the preignition rating test has been granted approval.

(i) Comparative single cylinder preignition test. This test should be con

ducted on a single cylinder engine acceptable to the FAA and should consist of the following: six approved spark plugs of a type currently considered acceptable for use in the obsolete engine and six test spark plugs of the type for which approval is desired should be tested to establish comparative preignition ratings. If the average IMEP rating of the test spark plugs falls within the range of plus or minus ten percent (±10%) of the average rating established for the approved type spark plugs, the test plug will be approved for limited use in an aircraft for the specific purpose of accomplishing one of the following flight service tests:

(a) When installed in not more than one-half of the engines of not more than two aircraft being operated under Parts 40, 41 or 42 of this subchapter, 150 hours of flight under normal operating conditions should be conducted and the spark plugs inspected in accordance with paragraph (c) (3) of this section at 25- to 30-hour intervals.

(b) When installed in engine(s) of not more than one aircraft being operated under Part 43 of this subchapter, 100 hours of flight under normal operating conditions should be conducted and the spark plugs inspected in accordance with paragraph (c) (3) of this section at 20- to 25-hour intervals.

(h) Spark plugs for obsolete 50-hour engines—(1) Spark plugs of new design. Either of the following procedures may be used to substantiate the airworthiness of spark plugs in this category:

(i) Block test. A 50-hour block test under conditions similar to those specified for the original type certification tests of the engine.

(ii) Ground and flight service test. (a) The ground test should be a 10hour endurance test under conditions similar to those specified for the original type certification of the engine.

(b) The flight portion of the test should be conducted under normal operating conditions for 90 hours on an experimental (NX) basis. The spark plugs should be inspected in accordance with paragraph (c) (3) of this section at 25- to 30-hour intervals.

(2) Spark plugs of a design similar to an approved type. Upon satisfactory completion of the preignition test and the flight service test specified below, spark plugs of a type, or similar to a

type which has been previously approved for use in one or more specific engine models, will be granted approval for use with all obsolete 50-hour engine models for which the approved spark plug used in the preignition rating test has been granted approval.

(i) Comparative single cylinder preignition test. The test procedures outlined in paragraph (g) (2) (i) should be followed.

(ii) Flight service test. Upon satisfactory completion of the preignition test a 50-hour flight service test should be conducted under normal operating conditions in one airplane only. The spark plugs should be inspected in accordance with paragraph (c) (3) of this section at 20- to 30-hour intervals.

to

(1) Alteration approved spark plugs (1) Major changes. Any major change to an approved type spark plug requires substantiation normally by engine testing. A description of the change and substantiating data should be submitted to the FAA for evaluation and/or approval to determine whether testing is necessary before installing the modified spark plug in a certificated engine. Major changes include:

(i) Any alteration or modification which will appreciably change the IMEP rating of the spark plug.

(ii) The substitution of nonequivalent materials for the fabrication of major parts and assemblies of the spark plug.

(iii) Any other change which may adversely affect the operating characteristics and the airworthiness of the spark plug.

(2) Minor changes. Minor changes do not require FAA approval prior to incorporation in certificated engines, but should be included in the semi-annual drawing submittal for subsequent FAA approval. Minor changes include:

(i) Slight variations in tolerances and clearances.

(ii) Change to equivalent or improved material in minor parts.

(iii) Improvements in surface treatment of external areas.

(iv) Any other minor change which does not adversely affect the operating characteristics and the airworthiness of the spark plug.

(3) Spark plugs tested by engine manufacturers. The spark plug manufacturer supplies detailed information

(usually on blue prints) to the engine manufacturer with respect to changes or alterations to approved type spark plugs. The engine manufacturer should include these changes in engine parts drawing submittals to the FAA.

(4) Spark plugs tested by others than engine manufacturers. Spark plug manufacturers and others who have obtained approval of a spark plug without testing by an engine manufacturer should submit all changes or alterations to the spark plug direct to the FAA.

(j) Spark plugs for military engines— (1) Military approved spark plugs. (i) Spark plugs approved by the military services for use in military engines whose commercial counterpart has been type certificated in accordance with CAR will be granted approval upon request for use in the civil counterpart of the military engine, providing their service experience in military operations has been satisfactory.

(ii) Spark plugs approved by the military services for use in a surplus military

engine model which has subsequently been certificated under Group 5-E Specifications of the Aircraft Engine Listing,' may be granted automatic approval for use in the engine, provided the military service experience of the spark plug has been satisfactory.

(2) Replacement spark plugs for military engines. (i) The test procedures outlined in paragraph (e), except paragraph (e) (2) (ii) (b) of this section, will apply to new or replacement spark plugs proposed for use in surplus military engines installed in aircraft being operated under Parts 40, 41 or 42 of this subchapter.

(ii) The test procedures outlined in paragraph (f), except paragraph (f) (2) (ii) (a) of this section, will apply to new or replacement spark plugs proposed for use in surplus military engines installed in aircraft being operated under Part 43 of this subchapter.

[Supp. 1, 19 F. R. 7998, Dec. 3, 1954]

The design and construction of the engine and the materials used shall be such as to minimize the possibility of occurrence and spread of fire because of structural failure, overheating, or other causes.

(b) External lines and fittings which convey flammable fluids shall be at least fire resistant. The possibility of flammable fluid carrying lines deteriorating from heat, vibration, or fluid pressure so as to cause a fire hazard shall be minimized by appropriate design, shielding, or routing. The fire-resistant standards of § 4b.1 (g) (2) of this subchapter shall be applicable.

[21 FR. 4305, June 20, 1956, as amended by Amdt. 13-1, 22 F.R. 5570, July 16, 1957] § 13.103

Vibration.

The engine shall be designed and constructed to function throughout its normal operating range of crankshaft rotational speeds and engine powers without inducing excessive stress in any of the engine parts because of vibration and without imparting excessive vibration forces to the aircraft structure.

§ 13.104 Durability.

All parts of the engine shall be designed and constructed to minimize the development of an unsafe condition of the engine between overhaul periods. Compressor and turbine rotor cases shall be designed to provide for containment of damage from rotor blade failure. [21 F.R. 4305, June 20, 1956, as amended by Amdt. 13-1, 22 F.R. 5570, July 16, 1957] § 13.110 Fuel and induction system.

(a) The fuel system of the engine shall be designed and constructed to supply an appropriate mixture of fuel to the cylinders throughout the complete operating range of the engine under all flight and atmospheric conditions.

(b) The intake passages of the engine through which air or fuel in combination with air passes for combustion purposes shall be designed and constructed to minimize the danger of ice accretion in such passages. The engine shall be designed and constructed to permit the use of a means for ice prevention.

(c) The type and degree of fuel filtering necessary for protection of the engine fuel system against foreign particles in the fuel shall be specified. It shall be demonstrated that foreign particles passing through the prescribed filtering means will not critically impair engine fuel system functioning.

(d) All passages in the induction system which conduct a mixture of fuel and air shall be self-draining, so as to prevent a liquid lock in the cylinders, in all attitudes which the applicant establishes as those the engine can have when the aircraft in which it is installed is in the static ground attitude.

[21 F.R. 4305, June 20, 1956, as amended by Amdt. 13-2, 23 F.R. 2594, Apr. 19, 1958; Amdt. 13-3, 24 F.R. 7077, Sept. 1, 1959]

§ 13.111 Ignition system.

All spark ignition engines shall be equipped with either a dual ignition system having at least two spark plugs per cylinder and two separate electrical circuits with separate sources of electrical energy, or with an ignition system which will function with equal reliability in flight.

§ 13.112 Lubrication system.

(a) The lubrication system of the engine shall be designed and constructed so that it will function properly in all flight

attitudes and atmospheric conditions in which the airplane is expected to operate.

(b) In wet sump engines the provision of paragraph (a) of this section shall be complied with when only one-half of the maximum lubricant supply is in the engine.

(c) The lubrication system of the engine shall be designed and constructed to permit the installation of a means for cooling of the lubricant.

(d) The engine shall be designed and constructed in such a manner that the crankcase is vented to the atmosphere so as to preclude leakage of oil resulting form excessive pressure within the crankcase.

[21 F.R. 4305, June 20, 1956, as amended by Amdt. 13-3, 24 F.R. 7077, Sept. 1, 1959] § 13.113 Engine cooling.

The engine shall be designed and constructed to provide the necessary cooling under conditions in which the airplane is expected to operate.

§ 13.114 Engine mounting attachments.

The mounting attachments and structure of the engine shall have sufficient strength, when the engine is mounted on an aircraft, to withstand the loads arising from the loading conditions prescribed in the airworthiness parts of the regulations in this subchapter applicable to the aircraft involved. § 13.115 Accessory attachments.

The de

Accessory drives and mounting attachments shall be designed and constructed so that the engine will operate properly with the accessories attached. sign of the engine shall incorporate provisions for the examination, adjustment, or removal of all essential engine accessories.

§ 13.116 Turbine rotors.

To minimize the probability of failure of turbine rotors, the provisions of paragraphs (a) and (b) of this section shall be complied with.

(a) Turbine rotors shall be demonstrated to provide sufficient strength to withstand damage inducing factors such as those which might result from abnormal rotor speeds, temperatures, or vibration.

(b) The design and functioning of ngine control devices, systems, and inumentation shall be such as to give

reasonable assurance that those engine operating limitations which affect turbine rotor structural integrity will not be exceeded in service.

[Amdt. 13–1, 22 FR. 5570, July 16, 1957] BLOCK TESTS

§ 13.150 General.

The engine, including all essential accessories, shall be subjected to the block tests and inspections prescribed in §§ 13.151 through 13.157.

§ 13.151 Vibration test.

A vibration survey shall be conducted to investigate crankshaft torsional and bending vibration characteristics over the operational range of crankshaft rotational speed and engine power normally used in flight (including low-power operation), from idling speed to either 110 percent of the desired maximum continuous speed rating, or 103 percent of the desired take-off speed rating, whichever is higher. The survey shall be conducted with a representative propeller. If a critical speed or speeds are found to be present in the operating range of the engine, changes in design of the engine shall be made for their elimination prior to the conduct of the endurance test specified in § 13.154, or the endurance test shall include operation under the most adverse vibration condition for a period sufficient to establish the ability of the engine to operate without fatigue failure.

§ 13.152 Calibration tests.

The engine shall be subjected to such calibration tests as are necessary to establish its power characteristics and the conditions for the endurance test specified in § 13.154. The results of the power characteristics calibration tests shall constitute the basis for establishing the characteristics of the engine over its entire operating range of crankshaft rotational speeds, manifold pressures, fuel/air mixture settings, and altitudes. Power ratings shall be based upon standard atmospheric conditions. (See also § 13.16 (d).)

§ 13.153 Detonation test.

A test shall be conducted to establish that the engine can function without detonation throughout its range of intended conditions of operation.

§ 13.154 Endurance test.

The endurance test of an engine with a representative propeller shall include a