AC NO: 20043C 

DATE: 10/20/76 

ADVISORY 

CIRCULAR 

DEPARTMENT OF TRANSPORTATION 

FEDERAL AVIATION ADMINISTRATION 

SUBJECT: AIRCRAFT FUEL CONTROL 

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1 . PURPOSE. This advisory circular alerts the aviation community to the 

potential hazards of inadvertent mixing or contamination of turbine 

and piston fuels, and provides recommended fuel control and servicing 

procedures. 

2 . CANCELLATION. Advisory Circular 20-43B, dated June 8, 19719 is 

canceled. 

* 3. REFERENCES. For more detail than is contained herein, see American 

Petroleum Institute Bulletins, Numbers 1523 Fourth Edition, 1542 Second Edition, 1581 First Edition, and the National Fire Protection 

Association Pamphlet "Aircraft Fuel Servicing lg'751f and the American 

Society for Testing and Materials, Wzandard Specification for Aviation 

Gasolines, D 910-75*1 * 

Initiated by: AFS-830 
AC 20-43C 10/20/76 

4 l BACKGROUND, Since the introduction of jet aircraft fuel, there have 

been several instances of inadvertent fueling of piston-powered aircraft 

with jet fuel. Aviation fuel can only serve its ultimate purpose when 

the PROPER fuel is delivered into the aircraft as free from contamination 

as it was the day it left the refinery. Unless care and ATTENTION are 

given to its handling, servicing, and storage, the many precautions 

taken in its manufacture and transportation are wasted. Close attention 

to compatibility of fuel and aircraft,as well as faithful adherence to 

good housekeeping practices,is necessary to prevent possible disaster as 

yell as costly contamination. A review of accidents attributed to fuel 

problems reveals that many power failures were due to use of improper 

fuel or careless senricing- fueling aircraft from poorly filtered .tanks, 

particularly small tanks or drums, improper mixing of fuel additives, 

improper preflight action by the pilot, and storing aircraft with partially filled tanks, etc., which invites condensation and contamination 

of-the fuel. It is well to remember that the consequences of using 

leaded gasoline in jet engines can be as d-aging as the &e of jet fuel 

in reciprocating engines. 

5 0 TURBINE(JET)FUELVERSUSGASOLINE. Investigation of a malfunctioning 

reciprocating engine disclosed that it had been inadvertently serviced 

with jet fuel. Examination of this engine revealed extensive cylinder 

assembly damage that required complete overhaul. Proper attention P -.-- 

to refueling would have prevented this damage. 

Frequency of improper fueling will diminish if owners, operators, and 

personnel servicing aircraft maintain vigilance. Should the occasion 

arise where the tanks in an aircraft are accidentally filled with jet 

fuel, it is suggested the following procedures be followed: 

a. If the engines were not operated subsequent to the refueling with 

jet fuel, drain the fuel tanks, lines, and system completely.S Refill 

the tanks with the proper grade of aviation gasoline, and run the 

engines for approximately five minutes. 

. 

b 0 If the engines were operated subsequent to the refueling with jet 

fuel, investigate any abnormal engine operating conditions such as 

those related to the fuel mixture and cylinder operating temperatures. 

In addition, accomplish the following: 

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10/20/76 AC 20-436 

(1) Perform a compression test of all cylinders. 

(2) Completely borescope inspect the interior of cylinders, 

giving special attention to the combustion ch&nber and the 

piston dome. 

' (3) Drain the engine oil and check the oil screens. 

NOTE: When accomplishing (l), (2), and (3), further investigate 

and correct any unsatisfactory condition found. 

(4) Completely drain the fuel tanks and the entire fuel system 

including the engine carburetor. 

(5) Flush the fuel system and carburetor with gasoline and check 

for leaks. 

(6) Fill the fuel tanks with the proper grade of aviation gasoline. 

(7) If the engine inspection was satisfactory, complete an engine 

runup check. 

* 6. AVIATION GASOLINE GRADES AND COLOR CODES. Pilots and refueling personnel 

should be familiar with aviation gasoline (avgas) grades and respective 

color codes in order to assure proper servicing of engines. Three grades 

of avgas are now produced for civil use; grades 80, 1OOLL (low lead) and 

100. These grades replace 80/87, 91/96, 100/130, and 115/145 avgas. 

a. The Standard Specification for Aviation Gasolines, Specification 

D 910-75, developed by the American Society for Testing and Materials, 

established that grade 80 should be red in color and contain 0.5 

milliliters (ml.) maximum of tetraethyl lead per gallon. Grade IOOLL 

is blue in color and contains 2.0 ml. maximum per gallon. Grade 100 

is green in color and contains 3.0 ml. maximum per gallon (with a 

probable increase to 4.0 ml. maximum per gallon in the next specification revision). The lead quantity or concentration of lead in aviation gasoline is expressed in terms of milliliters (l/1000 of a liter) 

per gallon of avgas. 

Grades 1OOLL and 100 represent two aviation gasolines which are 

identical in anti-knock quality but differ in maximum lead content 

and color. The color identifies the difference for those engines 

which have a low tolerance to lead. 

b. Limited-availability of grade 80 in some geographical areas of the 

country has forced owners/operators to use the next higher grade of 

avgas. Specific use of higher grades is dependent on the applicable 

manufacturer's recommendations. Continuous use of higher lead fuels * 

in low compression engines designed for low lead fuels can cause erosion or necking of the exhaust valve stems and spark plug lead fouling * 

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10/20/76 &AC 20-43C' 

7 l MARKING. 

a. Federal Aviation Regulations Part 23, Section 23.1557(c)(l), requires 

that aircraft fuel filler openings be marked to show the word rrFUEL*r 

and the minimum fuel grade or designation for the engines. In order 

that these markings retain their effectiveness, regulations also 

require that they be kept fresh and clean. It follows, therefore, 

that frequent washing and occasional painting will be necessary to 

retain clear legibility. 

b 0 It is equally important that tank vehicles be most conspicuously 

marked to show the type of fuel carried. It is suggested that the 

marking be of a color in sharp contrast to that of the vehicle and 

in lettering at least 12 inches tall. This marking should be on 

each side and on the rear of the tank vehicles. Additionally, it 

is suggested that the tank vehicle hose lines be marked by labels 

next to the nozzle and every six feet. The label lettering should 

be at least 3/4 inches in height, be of sharp color contrast, be 

permanently attached, and indicate the type of fuel dispersed by 

that hose. A further suggestion is that the refueling nozzles be 

conspicuously marked with the appropriate color code. This is especially important in that the person doing the refueling will have 

the color coded nozzle in his hands during the process with an additional reminder of the fuel type being dispensed. All of the aforementioned markings should be kept clean, fresh, and clearly legible 

at all times. 

8 0 TRAINING. Careful instructions in operating procedures should be given 

to all personnel involved in fueling. This applies to flight as well as 

ground personnel. The ground personnel should be thoroughly indoctrinated 

in the facilities, procedures, equipment, and the types of fuel being dispensed-the flight personnel in procedures and marking with particular 

emphasis on use of the proper type of fuel. It is further suggested that 

ALL personnel be retrained periodically with suitable records maintained 

to reflect the training. Fuel servicing should be performed only by 

trained competent personnel. 

9 . WHAT IS FUEL CONTAMINATION? Fuel is contaminated when it contains any 

material that was not provided under the fuel specification. This material generally consists of water, rust, sand, dust, microbial growth, and 

certain additives that are not compatible with the fuel, fuel system 

materials and engines. 

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10/20/76 AC 20-43C 

10 0 WHAT CAUSES FUEL CONTAMINATION? 

a. Water. All aviation fuels absorb moisture from the air and contain 

water in both suspended particle and liquid form. The amount of 

suspended particles varies with the temperature of the fuel. Whenever the temperature of the fuel is decreased, some of the suspended 

particles are drawn out ofthe solution and slowly fall to the bottom 

of the tank. Whenever the temperature of the fuel increases, water 

is drawn from the atmosphere to maintain a saturated solution. 

Changes in fuel temperature, therefore, result in a continuous 

accumulation of water. During freezing temperatures, this water 

may turn to ice, restricting or stopping fuel flow. 

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Rust, Pipelines, storage tanks, fuel trucks, and drum containers tend 

-produce rust that can be carried in the fuel in small size particles, A high degree of filtration is required to remove the liquid 

water and rust particles from the fuel. 

Dust and- sand. The fuel may be contaminated with dust and sand 

through openings in tanks and from the use of fuel-handling equipment 

that is not clean. 

Micr%organisms. Many types of microbes-have been found in utiea-ded 

fuels, particularly in the turbine engine fuels. The microbes, which . - 

may &&from the atmosphere -or stortige tanks,‘ live at the--interface b 

between the fuel and liquid water in the tank. These micro-organisms 

of bacteria and fungi rapidly multiply and cause serious corrosion in 

tanks and may clog filters, screens, and fuel metering equipment. The 

growth and corrosion are particularly serious in the presence of other 

forms of contamination. 

Additives. Certain oil companies, in developing products to cope with 

aircraft fuel icing problems, found that their products also checked * 

"bug" growth. These products, known as "biocides ft are usually referred to as additives, Some additives may not be'compatible with the 

fuel or the materials in the fuel system and may be harmful to other 

parts of the engine with which they come in contact. Additives that 

have not been approved by the manufacturer and FAA should not be used. 

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AC 20436 10/20/76 

11 l FIELLD TESTS. Three gallons of water were added to the half-full fuel 

tank of a popular make, high-wing monoplane. After several minutes, the 

fuel strainer (gascolator) was checked for water. It wasnecessary to 

drain ten liquid ounces of fuel before any water appeared. This is considerably more than most pilots drain when checking for water. 

In another test, simulating a tricycle geared model, one gallon of water 

was added to the half-full fuel tank. It was necessary to drain more 

than a quart of fuel before any water appeared. 

. In both of these tests, about nine ounces of water remained in the fuel 

tank after the belly drain and the fuel strainer (gascolator) had ceased 

to show any trace of water. This residual water could only be removed 

by draining the tank sumps. 

12 lCONTAMINATION CONTROL. The presence of any contamination in fuel systems is dangerous. Laboratory and field tests have demonstrated that 

when water was introduced into the gasoline tank, it immediately settled to the bottom. Fuel tanks are constructed with sumps to trap this 

water. It is practically impossible to drain all water from the tanks 

through the fuel lines, so it becomes necessary to regularly drain the 

fuel sumps in order to remove all water from the system. It may be 

necessary to gently rock the wings of some aircraft while draining the 

sumps to completely drain all the water. IOn certain tailwheel type 

aircraft, raising the tail to level flight attitude may result in additional flow of water to the gascolator or main fuel strainer. If left 

undrained, the water accumulates and will pass through the fuel line to 

the engine and may cause the engine to stop operating. The elimination 

of contaminants from aviation fuel may not be entirely possible, but we 

can control it by the application of good housekeeping habits. 

a. Servicing. Storage and dispensing equipment should be kept clean at 

all times-free from dirt and other foreign matter. Fuel having a 

"cloudy" appearance or definitely tloffcolor*T should.be suspected of 

contamination or deterioration and should not be used. When additives are used, it is important that they are dispensed in accordance with the aircraft manufacturer's instructions. 

Refueling from drums or cans should be considered as an unsatisfactory operation and one to be avoided whenever possible. All containers of this type are to be regarded with suspicion and the 

contents carefully inspected, identified, and checked for water and 

other contamin&tion. Extraordinary precautions are necessary to 

eliminate the hazards of water and sediment. It is advisable when 

fueling from drums to use a s-micron filtered portable pumping unit, 

or the best filtering equipment available locally, or, as a last 

resort, a chamois skin filter and filter funnel. 

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10/20/76 AC 20-43C 

Infrequently used fuel tanks should have their sumps drained before 

filling. Agitation action of fuel .entering the tank may suspend or 

entrain liquid water or other contaminants-which can remain suspended for many minutes and may not settle out until after the aircraft is airborne. 

b l Preflight action. Drain a generous sample of fuel--considerably more 

than just a trickle- into a transparent container from each of the 

fuel sumps and from the main fuel strainer or gascolator. (Remember 

that it was necessary to drain ten ounces in the field tests.) On 

certain aircraft having fuel tanks located in each wing, positioning 

of the fuel tank selector valve to the "BOTH ON!* position may not 

adequately drain the system. This is due to the fuel taking the 

path of least resistance. In this case, the fuel selector valve 

should be positioned at each tank in turn. 

Examine the fuel samples for water and dirt contamination. If present, it will collect at the bottom of the container and should be 

easily detected. Continue to drain fuel from the contaminated sump 

until certain the system is clear of all water and,dirt. 

**The use of quick-drain valves in the sumps and gascolator makes it practical to keep tanks free of significant quantities of water and other contaminants.T' 

c. Postflight. An effective method to prevent contamination from condensation would be to completely fill the fuel tank at the end of each 

day's flying. This procedure is practical only on a few types of 

light aircraft. Generally, the type of aircraft, length of proposed 

flight, number of passengers, and weight and balance limitations 

dictate the amount of fuel to be added. 

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WHAT’S WRONG WITH THIS PICTURE? 

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AC 2043C 10/20/76 

d l Routine maintenance. In addition to the preflight and postflight 

actions, certain precautionary or routine maintenance should be performed on the aircraft at periodic intervals. These precautions 

include the inspection and cleaning of pertinent fuel tank outlet 

finger strainers and carburetor screens (filters), and flushing of 

the carburetor bowl. 

13 0 JET FUELS. Turbine-powered aircraft, better known as "jet** or. **prop jet,” 

generally use a wide-cut gasoline or aviation kerosene as fuel. Basically, the same rules and precautions in handling aviation gasoline apply 

to the jet fuels. As with gasoline, we are concerned with the matter of 

cleanliness. Turbine fuels are more dense and have a greater viscosity 

(resistance to flow) than gasoline. It will hold and retain in suspension impurities such as water, fine particles of rust, and other foreign 

material. These particles can take from five to ten times as long, or even 

longer, to settle in kerosene as it does for them to settle in gasoline. 

Turbine engine fuel controls and pumps are generally more sensitive than 

the fuel systems of the piston engine. Their fuel feed and pumping systems must work harder. Tolerances are closer and fuel pressures higher. 

Fine contaminants may block fuel supply systems and erode critical parts 

of engine and fuel control systems. Water freezing at high altitudes 

may plug fuel screens. Because of these, the tolerable contaminationlevels for jet fuels are much lower than previously considered necessary 

for aviation gasoline. Even with the same contamination levels, the 

greater volume of fuel used by turbines results in greater amounts of 

contaminants being deposited in the turbine engine system. 

a. Test for contamination. 

ination are availa% 

Commercial products to test for fuel contamHere is a simple test to detect contamination 

of jet fuel. This procedure has proved to be both effective and 

inexpensive. 

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10/20/76 AC 20-43C 

l Obtain an unchipped, spotlessly clean, white enamel bucket (approximately ten-quart size). 

l Drain-about four to five inches of fuel, from the sump to be 

tested, into the bucket. 

l With a clean mixing paddle, .stir the fuel into a swirling Vornadoshaped%one. Remove paddle. As the swirling stops, the solid 

contaminants will gather at the center of the bucketbottom. . 

l Add several drops of household red food dye. The dye will mix 

with water and the solids in the bottom of the bucket. It will 

not mix with fuel. If no water is present, the dye will settle 

in the bottom of the bucket. 

14 a CONTAMINATED FUEL. Normally, upon finding that your fuel is contaminated 

by water or other foreign matter, the procedures noted under paragraph 

12, Contamination Control, should suffice. Should contamination persist, 

or if there is any doubt about it, your best bet is to have your aircraft 

fuel system inspected by a qualified person. 

15 l SUMMARY. So that your fuel system won't let you down when you want to 

stay up--remember: 

l Turbine fuels for turbine engines --gasoline of the proper grade for 

reciprocating engines. * 

l Use only.the fuel recommended by the engine and aircraft manufacturer. 

l Don’t use additives that have not been approved by FAA. 

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Ac.20-43c- 10/20/76 

l If feasible, keep fuel tanks full. Water condenses on the walls of 

partially filled tanks and enters the fuel system. 

l Filter all fuel entering the tank. 

l Drain fuel sumps regularly. 

l Periodically inspect and-clean all fuel strainers (screens) and 

occasionally.flush the carburetor bowl as recommended by the aircraft 

manufacturer. 

The best insurance-against fuel problems --whether aviation gasoline or 

jet fuel--is to practice good housekeeping in your routine maintenance 

and be constantly alert. 

FERRARESE, Acting Director 

Standards Senrice 

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