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.
23.1013 Oil tanks (Amendment 23-51)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.32
Paragraph 23.1013(a)
ADC Cross-reference: 5.32(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1013(b)
ADC Cross-reference: 5.32(b)
What is the difference between the expansion space requirements in § 33.71(c) and § 23.1013(b)?
The requirements of § 33.71(c) and § 23.1013(b) are similar, and both the engine manufacturer and the installer must show compliance to the oil tank expansion space requirement. When showing compliance with § 23.1013(b), data from the certification of the engine to § 33.71(c) may be used. Compliance with the installation requirements should account for any installation affects including wing dihedral, installed engine droop, and yaw angles. This could require ground test of both a left and right wing engine if adequate data is not available from the part 33 compliance demonstration.
Sometimes, the oil quantity in the tank may change with changing engine operating conditions such as engine rotation. This condition can result in overfilling the engine oil tank resulting in less than the required expansion space if the tank is serviced soon after engine shutdown. If conditions like this exist, they can be handled by oil system servicing limitations in the appropriate manuals with placards near the fill port.
Paragraph 23.1013(c)
ADC Cross-reference: 5.32(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.1013(d)
ADC Cross-reference: 5.32(d)
No specific policy is available as of December 31, 2002.
Paragraph 23.1013(e)
ADC Cross-reference: 5.32(e)
No specific policy is available as of December 31, 2002.
Related Material
AC 20-135, Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria
AC 23-2, Flammability Tests
NOTE. If there are differences between AC 20-135 and AC 23-2 (see below for AC title), the applicant may choose the advisory circular that is either most applicable or most advantageous, or both.
Paragraph 23.1013(f)
ADC Cross-reference: 5.32(f)
No specific policy is available as of December 31, 2002.
Paragraph 23.1013(g)
ADC Cross-reference: None
No specific policy is available as of December 31, 2002.
23.1015 Oil tank tests (Amendment 23-15)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.33
Paragraph 23.1015(a)
ADC Cross-reference: 5.33(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1015(b)
ADC Cross-reference: 5.33(b)
What test setup and procedures are typically used for the slosh test in § 23.1015(b)?
Refer to § 23.965(b) for a description of the test setup and procedure.
Related Material
TSO-C80, Flexible Fuel and Oil Cell Material
Paragraph 23.1015(c)
ADC Cross-reference: 5.33(c)
No specific policy is available as of December 31, 2002.
23.1017 Oil lines and fittings (Amendment 23-14)
CAR 3 Cross-reference: 3.570, 3.575
ADC Cross-reference: 5.34
Paragraph 23.1017(a)
ADC Cross-reference: 5.34(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1017(b)
ADC Cross-reference: 5.34(b)
No specific policy is available as of December 31, 2002.
23.1019 Oil strainer or filter (Amendment 23-43)
CAR 3 Cross-reference: 3.573
ADC Cross-reference: 5.35
Paragraph 23.1019(a)
ADC Cross-reference: 5.35(a)
Can the engine oil pressure indicator be used to comply with § 23.1019(a)(3)?
The engine oil pressure indication may be used as a method of detecting oil filter/strainer contamination provided the applicant demonstrates a procedure that does the following:
1. Identifies the oil strainer/filter contamination, and
2. Isolates the contamination as the sole cause of an indicated oil pressure change.
The procedure used to comply with § 23.1019(a)(3) should be documented in the Airplane Flight Manual.
Can a red warning light be use to comply with § 23.1019(a)(5)?
A red warning light is one means of complying with § 23.1019(a)(5).
Paragraph 23.1019(b)
ADC Cross-reference: 5.35(b)
No specific policy is available as of December 31, 2002.
23.1021 Oil system drains (Amendment 23-43)
CAR 3 Cross-reference: 3.574
ADC Cross-reference: 5.36, 5.36(a)
Paragraph 23.1021(a)
ADC Cross-reference: 5.36
No specific policy is available as of December 31, 2002.
Paragraph 23.1021(b)
ADC Cross-reference: 5.36(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.1021(c)
ADC Cross-reference: None
No specific policy is available as of December 31, 2002.
23.1023 Oil radiators (Original)
CAR 3 Cross-reference: 3.572
ADC Cross-reference: 5.37
No specific policy is available as of December 31, 2002.
23.1027 Propeller feathering system (Amendment 23-43)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.38
Related Material
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes
Paragraph 23.1027(a)
ADC Cross-reference: 5.38(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1027(b)
ADC Cross-reference: 5.38(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.1027(c)
ADC Cross-reference: 5.38(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.1027(d)
ADC Cross-reference: 5.38(d)
No specific policy is available as of December 31, 2002.
COOLING
23.1041 General (Amendment 23-51)
CAR 3 Cross-reference: 3.581
ADC Cross-reference: 5.39
When is testing required to show compliance with § 23.1041?
Sections 23.1043, 23.1045, and 23.1047 require testing to show compliance with § 23.1041.
What changes to an airplane would require testing to show compliance with § 23.1041?
Changes to an airplane that would require testing to show compliance with § 23.1041 could include, but are not limited to, the following:
1. Engine horsepower increase;
2. Nacelle changes, including cooling inlet modifications and blockage;
3. Adding or changing engine accessories such as turbochargers, generators, oil coolers, etcetera;
4. Changing the operating temperature limits of components in the nacelle; and
5. Propeller changes affecting climb or cruise performance.
What should be instrumented during the cooling tests on changes to airplanes?
The tests should be conducted to show the changed components remain within their temperature limits. During the testing, if negative impacts on other components are found, additional testing may be warranted to investigate these effects.
What altitudes are typically used for demonstrating compliance with the cooling requirements for reciprocating engine powered airplanes?
For reciprocating engines, cooling climb tests are typically commenced at pressure altitudes below 5,000 feet. The applicant should choose test conditions that are the most adverse for demonstrating engine and engine component cooling for the installation.
Related Material
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes 115
23.1043 Cooling tests (Amendment 23-51)
CAR 3 Cross-reference: 3.582, 3.583, 3.584, 3.585
ADC Cross-reference: 5.40
Paragraph 23.1043(a)
ADC Cross-reference: 5.40(a)
What are the typical means of complying with § 23.1043?
In general, the demonstration of compliance with this section requires analysis to identify areas of concern and instrumentation requirements and flight tests to demonstrate compliance. The applicant must identify all critical components (electronic components, actuators, etc.), fluids (engine oil, hydraulic fluid, etc.), and structures (primary composite structural elements, vibration isolators, etcetera) that have temperature limits.
The limits are typically based on component qualification testing. Each limit may be expressed as a fluid temperature, surface temperature, or environmental temperature and may have associated time limits. Instrumentation should be installed to provide data needed to show the corrected temperature for each critical component, fluid, and structure remains below the identified limit.
Are there any special considerations for special purpose, restricted category, singleengine agricultural airplanes using the normal category requirements of part 23 as a certification basis?
For these aircraft, conduct engine cooling test according to AC 23-8B, except as follows:
After the temperature has stabilized for the pre-takeoff holding condition on the taxiway, feather the propeller and record the data until the temperatures stabilize.
NOTE: This simulates normal agricultural operational engine running loading conditions. These criteria can be disregarded if the propeller is not feathered during normal agricultural operations on the ground.
Are there any special considerations for certificating winterization kits?
Winterization kits modify an airplane for operation in cold weather environments. These kits typically block or baffle air inlets to decrease mixing cold air in the engine compartments and keep the temperatures of fluids and components from falling below operating range. These kits can allow certification to lower ambient temperature operations than the standard 38 ºC (100 ºF). These limits must be reflected in the Airplane Flight Manual and placards on the equipment to indicate when the equipment should be removed. Additional guidance is available in paragraph 246 of AC 23-8B.