23.979 Pressure fueling systems (Amendment 23-51)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.23
Paragraph 23.979(a)
ADC Cross-reference: 5.23(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.979(b)
ADC Cross-reference: 5.23(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.979(c)
ADC Cross-reference: 5.23(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.979(d)
ADC Cross-reference: 5.23(d)
No specific policy is available as of December 31, 2002.
FUEL SYSTEM COMPONENTS
23.991 Fuel pumps (Amendment 23-43)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.24
Paragraph 23.991(a)
ADC Cross-reference: 5.24(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.991(b)
ADC Cross-reference: 5.24(b)
How are § 23.991(b) and § 23.991(c) related?
Paragraphs (b) and (c) are interrelated, and the interpretation of § 23.991(c) should consider § 23.991(b).
Both the main and emergency fuel pumps may operate continuously (simultaneously) provided there is a means to immediately indicate to the crew (in-flight) a malfunction of either pump.
A main fuel pump(s) supplies sufficient fuel to sustain the engine(s) during normal operations. An emergency fuel pump can sustain engine operation at full power in the event the engine-driven fuel-injector pump fails. An auxiliary fuel pump can provide some fuel flow during emergency operations but not enough to sustain engine operation at full power. Its function is to aid in priming the engine and suppressing fuel vapors.
Some fuel injection system designs utilize an integral speed-sensing pump, approved as part of the engine type design that delivers fuel at a (unregulated) pressure proportional to engine speed. Such systems have fuel lift capability that enables the system to function with a negative inlet pump pressure within specific limits as indicated by the engine type certificate data sheet (TCDS). For these types of fuel systems, an emergency fuel pump is not required when the injection pump is approved as part of the engine under § 23.991(b).
Other fuel injection system designs require an essentially constant (regulated) fuel pressure to the fuel-injector inlet. The acceptable pressure limits are specified on the engine TCDS. In these systems, the engine-driven fuel pump is functionally independent of the engine and not tied to the type design (regardless of the fuel pump supplier).
Consequently, these systems do require an emergency pump (according to 14 CFR part 23, § 23.991(b)) to ensure engine operation is sustained should the engine-driven pump fail.
Paragraph 23.991(c)
ADC Cross-reference: 5.24(c)
See paragraph (b) above.
Paragraph 23.991(d)
ADC Cross-reference: 5.24(d)
No specific policy is available as of December 31, 2002.
23.993 Fuel system lines and fittings (Amendment 23-43)
CAR 3 Cross-reference: 3.550
ADC Cross-reference: 5.25
Related Material:
AC 23-10, Auxiliary Fuel Systems for Reciprocating and Turbine Powered Part 23 Airplanes
Paragraph 23.993(a)
ADC Cross-reference: 5.25(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.993(b)
ADC Cross-reference: 5.25(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.993(c)
ADC Cross-reference: 5.25(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.993(d)
ADC Cross-reference: 5.25(d)
What does the term suitable for a particular application mean?
The term “suitable for a particular application” was incorporated by Amendment 23-43 (55 FR 40598, October 3, 1990) to remove the words “must be approved or.” This wording made § 23.993(d) more restrictive. All components are “approved” if they are installed on a certificated airplane; however, this in itself does not guarantee suitability.
For example, fuel hoses could be “approved” through the Technical Standard Order (TSO) system but still not be “suitable” for the environment of a particular installation.
Paragraph 23.993(e)
ADC Cross-reference: 5.25(e)
How is § 23.993(e) related to the powerplant cooling requirements?
Section § 23.1041 specified that there be provisions for maintaining the temperatures of powerplant components and fluids within their limits during various operations including shutdown. One such provision, as specified in § 23.993(e), is to not locate these items in areas exposed to unacceptable temperatures.
23.994 Fuel system components (Amendment 23-29)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.26
What is considered a hazardous quantity of fuel in § 23.994?
For the purpose of this section, “hazardous quantity” is defined as one quart, except a greater amount may escape if that greater amount can be substantiated as non-hazardous.
What other sections of the regulations are related to § 23.994?
The following sections are related to § 23.994 and may help determine the acceptability of the design.
§ 23.561 Emergency Landing Conditions, General
§ 23.721 Landing Gear, General
§ 23.863 Flammable fluid fire protection
§ 23.967(e) Fuel tank installation
§ 23.1189 Shutoff means
What are some typical methods used in complying with this rule?
The release of fuel from damaged fuel system components is the most likely cause of fire during a wheels-up landing on a paved runway. Therefore, the location and routing of fuel system components in the engine nacelle(s) and fuselage should be evaluated with respect to runway scraping and the resultant structural deformation. Particular attention should be paid to the release of fuel in areas with possible ignition sources such as electrical arcing and hot components. The following guidelines should be considered.
1. Design the fuel system to minimize the spilling or leaking of fuel and migration of the fuel into areas with likely ignition sources.
2. Locate and route the fuel system components as far as practicable from likely impact areas and areas where structural deformation may cause crushing, severing, punctures, rupture of frangible fittings, or high tensile loads in the lines.
3. Construct fuel lines to protect their integrity during and after a wheels-up landing.
The lines should allow stretching or movement with the deformed structure.
4. Isolate, separate, and route fuel lines and electrical wiring to the maximum extent practicable to minimize hazardous fuel spillage in these potential ignition source areas.
5. Shield and drain areas of potential fuel spillage away from potential ignition source areas.
6. Locate fuel shutoff valves outside areas of potential damage, such as engine nacelles, and design the valve support structures to maintain their integrity during and after the event.
7. Install auxiliary fuel tanks and systems based on the guidance in AC 23-10, Auxiliary Fuel Systems for Reciprocating and Turbine Powered Part 23 Airplanes.
23.995 Fuel valves and controls (Amendment 23-29)
CAR 3 Cross-reference: 3.551
ADC Cross-reference: 5.27
What rules are related to § 23.995?
See § 23.1189 Powerplant Fire Protection, Shutoff Means.
Paragraph 23.995(a)
ADC Cross-reference: 5.27(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.995(b)
ADC Cross-reference: 5.27(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.995(c)
ADC Cross-reference: 5.27(c)
What is a typical means of compliance for § 23.995(c)?
Compliance with this rule is usually accomplished by designing the fuel valve installation such that the valve is supported by primary or secondary airframe structure.
Paragraph 23.995(d)
ADC Cross-reference: 5.27(d)
No specific policy is available as of December 31, 2002.
Paragraph 23.995(e)
ADC Cross-reference: 5.27(e)
No specific policy is available as of December 31, 2002.
Paragraph 23.995(f)
ADC Cross-reference: 5.27(f)
No specific policy is available as of December 31, 2002.
Paragraph 23.995(g)
ADC Cross-reference: 5.27(g)
No specific policy is available as of December 31, 2002.
23.997 Fuel strainer or filter (Amendment 23-43)
CAR 3 Cross-reference: 3.552
ADC Cross-reference: 5.28
Does the powerplant installation require a fuel filter if the engine has one according to its type certificate?
Turbine engines certificated to 14 CFR part 33, § 33.67, Fuel system, Amendment 33-6 or subsequent, will include a fuel filter complying with § 23.997, and no airframesupplied filter is required. Turbine engines certificated prior to § 33.67, Amendment 33- 6, may require an airframe-supplied filter.
Reciprocating engines certificated to 14 CFR part 33, § 33.35 are not required to have a fuel filter as part of their certificated fuel system. The engine manufacturer is required only to specify the degree of filtering necessary and to verify that particles passing through the specified filter will not adversely affect the engine fuel system operation.
Because of this, an engine with a fuel filter certified to § 33.35 is not sufficient to meet all the requirements of § 23.997. To show compliance to § 23.997 for an engine with a filter, an airplane manufacturer would have to coordinate with the engine manufacturer on the filter installation to provide compliance data or add an airframe filter.
Paragraph 23.997(a)
ADC Cross-reference: 5.28(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.997(b)
ADC Cross-reference: 5.28(b)
No specific policy is available as of December 31, 2002.
Related Material
AC 23-15, Small Airplane Certification Compliance Program
Paragraph 23.997(c)
ADC Cross-reference: 5.28(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.997(d)
ADC Cross-reference: 5.28(d)
Is there any requirement for a pilot indication system relative to the fuel filter?
Section 23.1305 requires fuel flow indicators for both reciprocating and turbine-powered airplanes and a means to warn the pilot of fuel strainer or filter blockage before it reaches the capacity specified in § 23.997(d).
Paragraph 23.997(e)
ADC Cross-reference: None
No specific policy is available as of December 31, 2002.
Related Material
AC 23.1419-2B, Certification of Part 23 Airplanes for Flight in Icing Conditions
23.999 Fuel system drains (Amendment 23-43)
CAR 3 Cross-reference: 3.553
ADC Cross-reference: 5.29
Paragraph 23.999(a)
ADC Cross-reference: 5.29(a)
Where are drains typically located?
Usually more than one drain valve is required to drain the entire fuel system. These are typically located in fuel tank sumps, fuel line low spots, and in fuel filter/strainers.
Paragraph 23.999(b)
ADC Cross-reference: 5.29(b)
May a spring-loaded drain valve be used to comply with § 23.999(b)?
Spring-loaded drain valves may be used to comply with the positive locking provision of this paragraph in any region of positive fuel pressure. If a spring-loaded valve is located in a negative fuel pressure region (e.g., upstream of an engine-drive fuel pump providing suction lift), substantiate the installation by a test.
Related Material:
AC 20-119 Fuel Drain Valves