t 3 c/ 

U.S. Department 

of Transportation 

Federal Aviation 

Administration 

Advisory 

Circular 

Subject: QUALIFICATION OF FUELS, Date: 12/20/85 ACNo: 20-24B 

LUBRICANTS AXD ADDITIVES Initiated by: ApJF-110 Change: 

FOR AIRCRAFT ENGIVES 

1. PURPOSE 0 This'advisory circular (AC) describes procedures which may be 

used for approving the qualification of fuels, lubricants and additives for 

use in certificated aircraft engines. 

2 a CANCELLATION. AC No. 20024A, effective April 14, 1967, is cancelled. 

3 BACKGROUND l In certificating an engine, the Administrator has 

responsibility under Federal Aviation Regulations (FARs), Part 33, for 

establishing the limitations for the engine operation on the hasis of the 

operating conditions demonstrated during the block tests. Such operating 

limitations include those items relatfng to power, speeds, temperatures, 

pressures, fuels, and lubricants which are found to be necessary for safe 

operation of the engine. The limitations on fuels and lubricants include the 

additives that may be blended with the fuels or lubricants. The suitability 

and durability of all materials used in the engine are established on the 

basis of experience or tests, and all materials used in the engine must 

conform to approved specifications. Experience and test data should be on 

engine models which are, at minimum, similar in configuration, materials, 

operating characteristics, and power _ category to those of the engine in which 

these materials are intended for use. 

4 l DISCUSSION. Fuels and lubricants found to perform satisfactorily during 

the type cexfication program of an engine are approved as part of the Type 

Certificate (TC) and are listed on the pertinent Tvpe Certificate Data Sheet 

(TCDS). Issuance of the TC constitutes approval of-the fuel and lubricant 

specifications provided by the engine manufacturers. It is Federal Aviation 

Administration (FAA) policy that fuels and lubricants produced by companf.es 

other than those used in the type certification program may be used 

in a certificated engine provided the products meet the fuel(s) or 

lubricant(s) specification(s) for that engine. Fuels or lubricants that 

are not in conformance with the TC holder's approved specification listed 

on the TCDS, or a specification approved under a Supplemental Type 

Certificate (STC) are not eligible for use in a certificated.engine. These 

non-conforming fuels or lubricants must satisfy the certification 

requirements outlined in Paragraph 5 of this AC, PROCEDURE, in order to be 

approved. In addition, all synthetic lubricants are considered "new 

material" and must be individually approved. Additives to be used as a 

supplement to an approved fuel or lubricant also are considered to be a "new 

material" because their addition can significantly alter the physical and 

chemical properties of the fuel or lubricant These additives must he 
AC No. 20024B 

approved on an individual basis. In all cases, separate approval is 

required for each engine model or model series. In order to extend an 

approval from one model series on to another entire class of engines 

(i .e., all Lycoming non-supercharged direct drive engines up to 720 cubic 

inch displacement), it must be substantiated that the engine tested 

represents the most severe operating conditions of all the engines for 

which approval $s requested. For reciprocating engines, factors which 

should be considered include piston speeds, maximum RMEP, maximum cylinder 

and barrel temperature limits, turbocharger lubrication design, piston 

ring configurations, and gaskets, rings, and seals used in the engine and 

propeller oil system. Further, such materials are not eligible to be used 

in a certificated aircraft until the compatibility of these materials has 

been established with aircraft components (including propellers, where 

applicable) with which they come in contact. 

5 PROCEDURE. The producer of a product requiring an STC or an amendment 

ti an existing TC, as described in Paragraph 4 above, may apply to the 

Aircraft Certification Office (ACO) in the geographical area in which the 

applicant is located. The geographic AC0 will administer the program; 

however, the ultimate approval and issuance of the engine STC, or an 

amendment to an existing TC, is the responsiblity of the Engine and 

Propeller Certification Directorate located in the New England Region. 

Such STCs or amended TCs, may be approved for the fuels, lubricants, and 

additives for use in designated engine(s) upon receipt of suitable data 

demonstrating compliance with the applicable portions of FAR Part 33. 

The data should be obtained during an FAA approved and witnessed test 

program -- and should include the following: 

a. Preliminary Data - Prfor to FAA author%zatlon for test, the 

applicant should submit a report to substantiate that the fuels, 

lubricants, or additive combinations have undergone sufficient test and 

development to show that, under the conditions in which they will be used 

in the aircraft, they are compatible with the applfcahle engine and 

aircraft materials. The data should include compatibility with fuels, 

lubricants, and additives that are approved for the engfne, propellers 

(where applicable), and aircraft. For fuel additives, the additive must 

be soluble in the fuel at al1 anticipated temperatures; the blending 

procedures must be feasible; the additfve mtrst be shown not to congeal at 

cold temperatures, thereby clogging fuel lines and filters; the additfve 

must be compatible with other approved fuel additives (i.e., anti-icing 

additives); and the additive should not change fuel octane number. 

b. Test - A description of the test program and equipment that the 

applicant proposes to use in demonstrating the airworthfness of the 

material to be approved shall be submitted for approval. The engine(s) 

which are selected must be subjected to the pretest fnspection, FAR 33.42 

and 33.82; the calibration tests, FAR ,33.45 and 33,85; the endurance test, 

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AC No 20024B 

FAR 33.49 and 33.87; the operation test, FAR 33.51 and 33.89 and the 

teardown inspection, FAR 33.55 and 33.93. It is conceivable that the 

requirements of the operation test, FAR 33.51 and 33.89, can be satisfied 

concurrently with or as an addendum to the endurance test, FAR 33.49 and 

33.87. The applicant is requested to submit for FAA approval, the 

specific engine test procedure for each of the engines which N11 be 

subjected to .the 150-hour endurance test. This test procedure should 

provide all the specific information required to perform the test (i.e., 

test location, engine model to be tested, specific test hardware and 

instrumentation to he used, engine minimum and maximum operating 

parameters, the engine lubricant to be used, the lubricant change 

interval, a list of all information to be recorded during the test 

including changes to oil properties, the intervals at wMch this data is 

to be recorded, etc.) In addition, in accordance with FAR 33.53 and 

33.91, engine component test, a test should be performed with the 

objective of showing that the subject material will not cause 

deterioration or any other unsatisfactorv condition on or in any of the 

non-metallic engine oil-wetted parts useb in any of the engines in which 

the additive is used. A SOO-hour controlled flight test, under the test 

conditions listed below, may be considered as an equivalent for the 

.endurance portion of the requirements of FAR 33.49 and 33.87, when 

followed bv a complete teardown inspection: . 

Takeoff power or thrust 5 hours minimum 

Fax. continuous power or thrust . 20 hours minimum 

Cruise power or thrust 450 hours minimum 

Idle 25 hours minimum 

c. Final Data - At the .completion of the aircraft engine tests, a 

report should be submitted which includes, at minimum, the following: 

(1) A description of the engine in which the material was tested. 

(2) A chronological history of test conditions and engine 

performance, including r.p.m ., power or thrust levels achieved during the 

test, fuel and oil consumption, oil changes, parts replacement, and other 

pertinent test results. 

(3) An analysis of lubricating oil samples taken before and after 

the test, and before each oil change. These analvzes are required for 

both fuel and oil substantiation testing. 

(4) An analysis of the fuel used during the test. For fuel 

substantiation testing, these analyzes must demonstrate minimum or "worst 

case" properties. 

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AC No. 20024B 

(5) Evidence that abnormal wear, deposits metal attack, or 

other harmful effects did not occur as a result of the material under 

test. 

(6) Evidence to establish that deterioration, excessive seal 

swelling, shrinkage, hardness, or unsatisfactory condition on or in.any of 

the non-metallic engine oil-wetted parts did not occur as the result of 

the material under test. 

d 0 Identification - The material tested must be covered by a 

specification that is written in sufficient detail to provide, at minimum, 

the physical properties and limits by which uniform quality and 

composition can be maintained, If the material Is to be used in a blend 

with another material, instructions for blending should be provided which 

include safety precautions. 

e. Concentration - The materials tested should be approved for use 

only in the concentrations "up to the maximum" at which they were 

qualified by test. 

obert E. Whittington 

New England Region 

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