Related Material
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes
Paragraph 23.1043(b)
ADC Cross-reference: 5.40(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.1043 (c)
ADC Cross-reference: 5.40(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.1043 (d)
ADC Cross-reference: 5.40(d)
No specific policy is available as of December 31, 2002.
Related Material
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes
23.1045 Cooling test procedures for turbine engine powered airplanes (Amendment 23-51)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.41, 5.41(a), 5.41(b), 5.41(c), 5.41(d)
Related Material
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes
Paragraph 23.1045(a)
ADC Cross-reference: 5.41(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1045(b)
ADC Cross-reference: 5.41(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.1045(c)
ADC Cross-reference: 5.41(c)
No specific policy is available as of December 31, 2002.
23.1047 Cooling test procedures for reciprocating engine powered airplanes (Amendment 23-51)
CAR 3 Cross-reference: 3.587
ADC Cross-reference: 5.41, 5.41(a), 5.41(b), 5.41(c), 5.41(e)
No specific policy is available as of December 31, 2002.
Related Material
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes
LIQUID COOLING
23.1061 Installation (Amendment 23-43)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.42
Paragraph 23.1061(a)
ADC Cross-reference: 5.42(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1061(b)
ADC Cross-reference: 5.42(b)
No specific policy is available as of December 31, 2002.
Paragraph 23.1061(c)
ADC Cross-reference: 5.42(c)
No specific policy is available as of December 31, 2002.
Paragraph 23.1061(d)
ADC Cross-reference: 5.42(d)
No specific policy is available as of December 31, 2002.
Paragraph 23.1061(e)
ADC Cross-reference: 5.42(e)
No specific policy is available as of December 31, 2002.
Paragraph 23.1061(f)
ADC Cross-reference: 5.42(f)
No specific policy is available as of December 31, 2002.
23.1063 Coolant tank tests (Original)
CAR 3 Cross-reference: None
ADC Cross-reference: 5.43
Paragraph 23.1063(a)
ADC Cross-reference: 5.43(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1063(b)
ADC Cross-reference: 5.43(b)
No specific policy is available as of December 31, 2002.
INDUCTION SYSTEM
23.1091 Air induction system (Amendment 23-51)
CAR 3 Cross-reference: 3.605
ADC Cross-reference: 5.44
Related Material
AC 20-135, Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria
Paragraph 23.1091(a)
ADC Cross-reference: 5.44(a)
No specific policy is available as of December 31, 2002.
Paragraph 23.1091(b)
ADC Cross-reference: 5.44(b)
No specific policy is available as of December 31, 2002.
Related Material
AC 23-2, Flammability Tests
Paragraph 23.1091(c)
ADC Cross-reference: 5.44(c)
What is considered a hazardous quantity in § 23.1091(c)?
A hazardous quantity is defined as one that if ingested into the engine inlet would cause the engine to exceed its operational limitations, cause a significant loss of power, or otherwise cause the engine to operate in an unsafe condition.
Related Material
AC 20-124, Water Ingestion Testing for Turbine Powered Airplanes
23.1093 Induction system icing protection (Amendment 23-51)
CAR 3 Cross-reference: 3.606
ADC Cross-reference: 5.45
Is an airplane required to comply with § 23.1093 if it is not being certificated to fly in icing conditions?
Yes, compliance with § 23.1093(b) for induction system icing protection is required for all normal, utility, acrobatic, and commuter category airplanes certificated under part 23 even if the airplane is not being certificated for flight in icing conditions (§ 23.1419 compliance). Service experience has shown that airplanes can inadvertently encounter icing conditions even if the airplane is not approved for flight into icing conditions. This is particularly true for turbine engine powered airplanes, which typically have a greater operating flight envelope than reciprocating engine powered airplanes. These requirements are also those demonstrated during engine certification (reference 14 CFR part 33, subpart E, § 33.68, Induction system icing, for turbine aircraft engines).
What other icing related sections of 14 CFR part 23 cover the propulsion systems?
Sections 23.901(d)(2), 23.929, and 23.975(a)(1) address engine ice ingestion capability, engine installations including propellers, and fuel tank venting, respectively.
Are all icing related sections of 14 CFR part 23 that cover the propulsion systems required for airplanes not being certificated to fly in icing conditions?
Airplanes not being certified for flight into icing conditions according to § 23.1419 do not have to demonstrate compliance with § 23.929.
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?
An exemption to the requirements of § 23.1093 is possible for single-engine piston or turbopropeller airplanes certificated under 14 CFR part 21, § 21.25(a), for special purpose agricultural operations. A limitation in the Airplane Flight Manual, such as “Operation of the airplane in visible moisture below 40 °F is prohibited,” will be enough to address this regulation for these non-standard category airplanes.
What methods can be used to show compliance with § 23.1093?
Compliance with § 23.1093 can be shown using an appropriate combination of the methods listed and described below.
1. Compliance with part 33 icing requirements
2. Similarity and service experience
3. Analysis
4. Ground testing
5. Flight testing with an airborne icing tanker
6. Flight testing in natural icing conditions
How can the part 33 engine certification be used to demonstrate compliance?
Engine certification to part 33 does not fully address all the part 23 engine installation requirements. For example, part 33 engine certification does not address snow ingestion.
It is the responsibility of the airplane applicant and not the engine manufacturer to show compliance with the part 23 induction system ice protection requirements.
An applicant seeking airplane certification should coordinate the installation of an engine with the engine manufacturer. The engine manufacturer should be able to identify critical points, conditions, and operational requirements that may need to be addressed when showing compliance with the installation requirements. Engine type certification data can be used as the basis for reducing design risk, analysis, and testing when showing compliance with § 23.1093. The airplane applicant should evaluate the engine type certification data and demonstrate how the data is applicable to the particular installation.
For example, the use of an inlet system recommended by the engine manufacturer would still require installation substantiation to show compliance with part 23 requirements.
How can similarity and service experience be used for compliance?
The use of similarity and service experience is appropriate to lessen the design risk associated with an installation. Once an applicant has developed data on an installation, the applicant may then use this data, when suitable, for substantiation on later projects with similar installations. It is common and proper for an applicant to base analytical methods and test point definitions on experience and testing from previous, similar certification programs performed by the applicant. Certification is based on the analysis and testing of an airplane’s type design. Because of this, it is difficult to show similarity to an airplane configuration certified by another applicant without direct access to the type design data used for that certification.
Even if previous experience and data are used, each inlet/engine installation and the associated operating characteristics can be different and should be considered individually. Therefore, it is not appropriate to use similarity or service experience by itself to demonstrate compliance to the § 23.1093 requirements. Rather, such means as 124
similarity or service experience should be supplemented with either analysis, even if only basic design analysis to substantiate similarity, or testing, or a combination of both.
Can compliance with § 23.1093 be accomplished with analysis alone?
No, analysis alone is not sufficient to show compliance. Testing is normally required to demonstrate compliance as analytical methods have been difficult to validate. It is possible, for airplanes not being certified to § 23.1419, that flight testing will not be required given analysis that is backed by similarity to and service experience of other certified installations.
How can ground testing be used to show compliance?
Artificial icing conditions can be generated in icing tunnel facilities. Artificial icing for compliance to ground ice fog requirements can also be generated with an icing spray rig set up in front of the airplane. The icing conditions are very dependent on the calibration of the nozzles. SAE ARP 5905 contains calibration guidelines for icing tunnels. The personnel operating icing spray rigs should be familiar with the calibration of icing nozzles.
Artificial snow can be generated in some ground facilities to supplement natural snow testing. Considerations are provided in the discussion under § 23.1093(b).
How can tunnel test data be used for compliance?
An area where there has been much discussion has been the use of tunnel test data instead of full-scale, airplane flight test data for showing compliance with § 23.1093. The use of tunnel test data is a common, appropriate, and often efficient means to reduce the amount of testing required by the applicant for showing compliance. However, the extent that this data can be used for compliance is dependent upon how representative the test article and test conditions are to the installation and airplane operating conditions.
It is not uncommon for tunnel testing to be performed on a prototype or test inlet that often has design differences from the production inlet used by an installer. When using tunnel test data, or any test data for that matter, as a basis for testing or certification, the applicant must address the differences and the impact of the differences. Three areas of difference usually addressed include the following:
1. Heated versus non-heated inlets;
2. Inlets with movable or variable internal devices (for example, movable vanes used to select bypass modes on a number of turbopropeller inlets) versus fixed inlets; and
3. Differences in geometry even if the inlet type (fixed versus variable) is the same.
As an example, if tunnel testing is performed with a heated inlet and an applicant incorporates a non-heated inlet, ice runback/refreeze may be reduced, but items such as ice accretion characteristics will be different.
It must be ensured that the tunnel tests were performed at the critical points. Advisory Circular 20-73, Aircraft Ice Protection, provides guidance on critical points determination.
How can testing with airborne icing tankers be used for compliance?
Tanker icing tests are not used as a sole means of compliance, but may be used:
1. To verify analyses or scaled icing tunnel tests
2. To obtain data at the limits of the Appendix C icing envelopes
3. To evaluate ice-shedding characteristics
SAE ARP 5904 provides useful information on icing tanker testing.
One limitation of icing tankers in the past has been their inability to generate droplet sizes at the low end of the Appendix C envelope, which may be critical for inlets with curves and bends, such as some turboprop inertial separation inlets.
How can flight test in natural icing conditions be used for compliance?
Airplanes being certified for flight into icing conditions according to § 23.1419 will require flight test into natural icing conditions. The results of this testing can be used to show compliance with § 23.1093.
Airplanes not being certified for flight into icing conditions according to § 23.1419 do not necessarily require flight test into natural icing conditions to show compliance with § 23.1093. It is acceptable to use analysis backed with sufficient similarity and service experience to show compliance.
Related Material
AC 20-73, Aircraft Ice Protection
AC 23-8B, Flight Test Guide for Certification of Part 23 Airplanes
AC 23.1521-1B, Type Certification of Automobile Gasoline in Part 23 Airplanes with Reciprocating Engines
SAE ARP 5904, Airborne Icing Tankers
SAE ARP 5905, Calibration and Acceptance of Icing Wind Tunnels
Paragraph 23.1093(a)
ADC Cross-reference: 5.45(a)
What does the term preheat mean and how is it different from heat rise?
Current interpretation of the term preheat as written in § 23.1093(a)(4) and § 23.1093(a)(6) is that it is a change in temperature above the ambient requirements stated in the regulation. Thus, it is interpreted as interchangeable with the term heat rise.
The regulation is written to provide rules of compliance that can be reasonably demonstrated without testing over the whole range of the icing and engine power envelopes. According to Appendix C of part 25, the icing temperature envelope extends down to -22 °F, a condition that is difficult to attain during a normal flight test program.
The interpretation of § 23.1093(a)(6) is that a “preheat of 60 °F” requires a change of 60 °F above the 30 °F ambient baseline temperature. This interpretation ensures that the system will always provide sufficiently heated air to prevent icing even if the airplane encounters the worse case scenario with –22 °F temperatures and the engines at idle as with a descent to landing.
Related Material
AC 23.1419-2B, Certification of Part 23 Airplanes for Flight in Icing Conditions
Paragraph 23.1093(b)
ADC Cross-reference: 5.45(b)
Why are the falling and blowing snow requirements separate from the icing and water ingestion requirements?
The falling and blowing snow requirement was incorporated separately from the icing and water ingestion requirements due to the unique characteristics of snow. The requirement contained in § 23.1093(b)(1)(ii), incorporated initially by Amendment 23- 15, is to evaluate the installed powerplant system to ensure that no hazardous effects are encountered when operating in falling and blowing snow. A hazardous effect could be unacceptable engine operating characteristics (for example, adverse power loss, surges, and so forth) due to inlet blockage or engine damage resulting from conditions such as snow, which may accumulate, melt, refreeze, shed, and then be ingested by the engine.
Therefore, compliance with engine induction system icing requirements does not show compliance with the snow requirements in § 23.1093(b)(1)(ii).
What should be considered relative to complying with the falling and blowing snow requirements?
The effect of ingesting snow during ground operations and critical in-flight operations should be evaluated. Service experience has demonstrated that engine damage can occur as a result of prolonged ground operations in falling and blowing snow. Also, in-flight service experience has shown that snow, which has melted and refrozen, can shed from engine, inlet, or airplane accumulation sites, resulting in adverse engine operability or engine damage. The critical snow environment is a ”wet, sticky snow,” which accumulates on unheated exterior and interior surfaces subject to impingement.
When showing compliance with § 23.1093(b)(1)(ii), the installation should be reviewed to identify potential inlet, engine, and airframe sites where snow accumulation and shedding is possible. The airplane ground and in-flight operational envelope should be reviewed to determine critical conditions that should be addressed. The information from these reviews should be used to identify the critical conditions to evaluate compliance.
The following differences between turbopropeller and turbofan/jet installations should be considered:
1. Typical turbopropeller installations have inlets that incorporate complex geometry with features such as particle separators, plenum chambers, screens, oil coolers, and so forth, where hazardous snow accumulations may occur. Turbopropeller installations normally require testing in operationally representative conditions.
2. Typical turbofan/jet installations, using simple pitot (straight duct) inlets, have minimal, if any, areas for snow accumulation. For these inlets, in-flight icing tests have generally been found to be more critical than snow tests. Turbofan/jet installation may be found acceptable by inlet design and airplane operation analysis.
Care should be taken to identify potential airplane accumulation sites that could shed into the engine(s), such as in the case of aft-mounted engines. Atypical installations with S-type inlet geometries should be treated like the turbopropeller installations when finding compliance with § 23.1093(b)(1)(ii).
What operationally representative condition should be considered?
When evaluating the conditions for showing compliance, the following airplane operations should be considered:
1. Takeoff power after static operation with the engine at idle for 30 minutes.
This condition is considered critical due to the operational consideration of idling an engine on the ground with minimal ability for de-ice/anti-ice. The primary concern is the loss of power at takeoff roll.
It is acceptable to incorporate engine run-up to higher power settings during the 30 minute period for the purposes of ice/snow shed, provided the procedure does not 128