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
23.1001 Fuel jettisoning system (Amendment 23-51)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.30
Related Material
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes
Paragraph 23.1001(a)
ADC Cross-reference: 5.30
What is the definition of maximum weight as used in § 23.1001(a)?
The maximum weight to be used in calculating the fuel jettison rate is the maximum takeoff weight of the airplane. This is supported by Amendment 23-7, which, for the most part, used the requirements of § 25.1001 as a new § 23.1001. At the time, § 25.1001 stated that the calculation was to use maximum takeoff weight.
Paragraph 23.1001(b)
ADC Cross-reference: 5.30(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1001(c)
ADC Cross-reference: 5.30(a)(1), 5.30(a)(2), 5.30(a)(3), 5.30(a)(4)
What methods are typically used to show compliance with § 23.1001(c)?
Colored fuel or a surface treatment that changes appearance upon contact with fuel or fuel vapor has been used to detect surface impingement. Combustible mixture detectors, scent, or visual inspections have been used to detect fuel or fuel vapor entering portions of the airplane.
Paragraph 23.1001(d)
ADC Cross-reference: None
No specific policy is available as of December 31, 2002.
Paragraph 23.1001(e)
ADC Cross-reference: None
No specific policy is available as of December 31, 2002.
Paragraph 23.1001(f)
ADC Cross-reference: 5.30(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.1001(g)
ADC Cross-reference: 5.30(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.1001(h)
ADC Cross-reference: 5.30(d)
No specific policy is available as of December 31, 2002.
OIL SYSTEM
23.1011 General (Amendment 23-43)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.31
Paragraph 23.1011(a)
ADC Cross-reference: None
This guidance may be used for Airship Certification as applicable.
Can the part 33 certification of oil system components be used to show compliance with § 23.1011?
Oil systems and components certified with the engine may or may not be suitable for use in a specific airplane installation, depending upon the test/analysis performed at the time.
Also, engines may be originally certified with the intention of being installed in different airplanes than where they are eventually used. Consequently, oil systems and components approved during engine type certification are only acceptable for use without further substantiation when they complied with standards that are equal or more stringent than those in this subpart.
Evaluate each pertinent item in the installation to assess the airplane requirements versus the requirements demonstrated during engine certification. Verify the latter with the engine manufacturer or the FAA office controlling the engine type design.
Paragraph 23.1011(b)
ADC Cross-reference: 5.31(a)
What are the requirements for continued safe operation of the engine(s)?
The engine requirements for oil quantities and temperatures are established by the engine manufacturer and may be found on the Type Certification Data Sheet or in the engine installation manual. The airplane installation must not cause the engine limits to be exceeded under normal operations.
Paragraph 23.1011(c)
ADC Cross-reference: 5.31(b)
How much oil must the system contain?
Paragraph 23.1011(c) requires that, “The usable oil tank capacity may not be less than the product of the endurance of the airplane under critical operating conditions and the maximum oil consumption of the engine under the same conditions, plus a suitable margin to ensure adequate circulation and cooling.” In other words, there needs to be enough oil (usable supply) to allow the engine to consume the usable fuel. This should be substantiated by a quantitative analysis.
In addition, a suitable oil quantity margin for system circulation is necessary for all engine installations. The oil system should be capable of maintaining the engine within its operating limitations (i.e., oil temperature with the minimum oil quantity provided for circulation). Cooling tests do not need to be performed with a low usable oil supply provided the oil is properly cooled at all oil levels.
What are the definitions of some of the terms used to determine the required oil quantity?
Usable Oil
Usable oil is defined as the quantity of oil in the oil tank (or sump in the case of wet sump engines) in excess of the minimum quantity of oil required to keep the oil pump inlet feed covered under the most adverse operating condition.
Without any other data, the most severe of the following two conditions may be used as the most adverse operating condition (in both cases, with the airplane at a zerodegree roll angle):
1. The nose-up pitch angle required for the sea level best rate-of-climb speed with maximum continuous power, or
2. The nose-down pitch angle required for the 1.3 V SO power-off landing configuration.
For most wet sump engines, the usable oil quantity for various pitch angles is listed on the appropriate engine Type Certificate Data Sheet (TCDS). This quantity may be used instead of a determination of usable oil as described above. If the usable quantity is not listed, it may be determined by contacting the engine manufacturer or conducting a usable oil test with the critical operating conditions.
Usable Fuel
The usable quantity of fuel is established under § 23.959.
Specific Oil Consumption (SOC)
The SOC is the maximum oil consumption rates established by the engine’s manufacturer, expressed in pounds per brake horsepower per hour (lb./bhp/hr.). If such a maximum oil consumption rate is not available, use 0.012 lb./bhp/hr. for reciprocating engines. There is no similar “default” maximum oil consumption rate for turbine engines.
You can also establish an oil consumption rate by the following:
1. Statistical analysis of actual in-service oil consumption rates. The analysis should include observed data on the actual oil consumption from statistically valid sample engines of the same model. These data should be obtained from high time engines or those with high oil consumption just before removal for overhaul.
2. Testing according to an FAA-approved test plan. Testing for a lower oil consumption rate should include a positive demonstration that a lower oil consumption rate will not jeopardize the airworthiness of the engine.
Specific Fuel Consumption (SFC)
SFC is the fuel consumption established for the engine based on available engine power expressed in pounds per brake horsepower per hour.
What are the acceptable means of compliance for § 23.1011(c)?
Single-engine Installations
Determine the minimum allowable usable oil capacity from the airplane’s endurance (~total fuel capacity divided by the minimum SFC) and the maximum allowable oil consumption rate. For either wet or dry sump engines, this is expressed mathematically as follows:
[Minimum Usable Oil Capacity (lbs.)] =
[Maximum Usable Fuel Capacity (lbs.)] x [Maximum SOC (lb./bhp/hr.)] [Minimum Obtainable SFC (lb./bhp/hr.)]
A usable oil capacity greater than or equal to the calculated number above is acceptable.
Multiengine Installations
Calculate the minimum usable oil capacity for a multiengine aircraft as above, except modify as follows:
Account for the additional usable fuel if the airplane has a fuel cross-feed system or common fuel tank in the event of an engine shutdown. Allocate 50 percent of the maximum usable fuel capacity attributable to the shutdown engine as available to the other engine(s). For example, for a twin-engine airplane with 1,000 pounds of maximum usable fuel, 500 pounds of which is attributed to the shutdown engine, add 50 percent of that (250 pounds) to the available fuel.
In addition, adjust the fuel consumption of the remaining engine(s) to reflect any power or mixture setting changes made to complete the flight safely.
Paragraph 23.1011(d)
ADC Cross-reference: 5.31(c)
What oil quantity should be used in finding compliance with § 23.1011(d)?
A conventional system (no transfer system provided) should only consider the usable oil tank or sump capacity to determine the usable oil supply. Do not consider the quantity of oil in the engine oil lines, in the oil radiator, oil filter, propeller feathering reserve, etc. If the airplane manufacturer elects to operate the engine with less than total oil capacity, the lower oil level should be used in the analysis.
Paragraph 23.1011(e)
ADC Cross-reference: 5.31(d)
Is it possible to consider oil in transfer lines as part of the usable oil?
When an oil reserve system is installed, additional oil may be available. The system is often configured so the transfer pump can pump oil into the main engine oil tank(s) from the transfer lines. In this case, include the quantity of oil that would be pumped to the main engine oil tank(s) to determine the usable oil supply.