CHAPTER 2. INTRODUCTION
1. Why write this AC?
a. The Safer Skies initiative and the Advanced General Aviation Transportation Experiment (AGATE) program determined that modern avionics could provide pilots with better information and reduce general aviation accidents. Until recently, hardware costs and certification costs made it impractical to build new technology avionics systems for part 23 use. As new technology is introduced, hardware costs continue to come down. In contrast, the avionics installation approval process has increasingly become more rigorous for applicants seeking installation approval of new systems in part 23 and CAR 3 airplanes. Also, the existing approval processes often provide an inconsistent level of FAA oversight.
b. Applicants sought the approval path of least resistance, which has increased the number of follow-on field approvals for installation of avionics systems in small airplanes. Field approvals are typically based on a single STC with little or no follow-on ACO involvement, which may only be suitable for certain types of installations. For more complex avionics installations, a follow-on field approval may not properly address interface considerations to existing equipment. This warrants a change in the avionics approval process for part 23 and CAR 3 airplanes. The resulting streamlined process needs to provide the proper measure of certification oversight, but it must provide similar advantages to the field approval process.
c. The “Industry and FAA Avionics Approval Guide” describes the certification process for design and installation approval and suggests expanded use of the AML process to streamline part 23 avionics installation approvals. However, the lack of clear guidance on AML approvals has led ACOs to develop their own avionics approval procedures, resulting in a lack of standardization. There is a clear need for a standardized approach to the AML avionics approval process, including criteria for the suitable use of the process, which this AC is designed to provide.
d. Existing AML approvals range in complexity from simple “single wire” installations of supplemental systems to complex Primary Flight Display (PFD) systems that provide flight critical information. Each avionics system presents a unique set of certification requirements. Complex systems require greater certification detail to deal properly with compliance issues for models with slightly different certification bases.
For example, showings of compliance to part 23, § 23.1331 requirements for electrical power may be slightly different from model to model and must be clearly documented under the AML process.
e. This AC serves to clarify the AML process for part 23 avionics approvals. It clearly outlines the requirements for creating a Model Qualification Process, determining a suitable certification basis, creating detailed installation instructions with equipment suitable integration procedures, determining data package details, creating procedures for amending the AML, and other items. The AML process is designed to allow a single set of compliance data to be applied to multiple models, where suitable. The intent is to 3
avoid duplication of testing and data gathering while honoring the agency's primary responsibility to determine the airworthiness of the altered product.
f. It is important the applicant and the FAA ACO agree to the use of the AML process early in a certification project. The resulting STC, with its associated AML, should lessen the need for installers to request field approvals, but is not meant to lower the certification requirements for a particular installation approval. If done properly, an AML STC may save valuable resources for both industry and the FAA by reducing the number of individual STC approvals.
2. What documents are related to this AC?
a. Orders, regulations, policy statements, and other FAA documents:
HBAW 98-18 Checklist for Instructions for Continued Airworthiness for Major Alterations
Order 8100.5A Aircraft Certification Service Mission, Responsibilities, Relationships, and Programs
Order 8110.4B Type Certification
Order 8150.1B Technical Standard Order Procedures
Order 8300.10 Airworthiness Inspector’s Handbook Volume 2, Chapter 1, Perform Field Approval of Major Repairs and Major Alterations, Change 16
Order 8110.37C Designated Engineering Representative (DER) Guidance Handbook
Order 8110.48 How To Establish The Certification Basis For Changed Aeronautical Products
Order 8110.49 Software Approval Guidelines
Title 14 CFR, part 21 Certification Procedures for Products and Parts
Title 14 CFR, part 23 Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter Category Airplanes 4
b. Advisory Circulars
You may get copies of the current publication of the ACs listed below from the U.S.
Department of Transportation, Subsequent Distribution Office, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785. The ACs are also available on the Internet at http://www.faa.gov/certification/aircraft.
AC 21-40 Application Guide for Obtaining a Supplemental Type Certificate
AC 23.1309-1C Equipment, Systems, and Installation in Part 23 Airplanes
AC 23.1311-1A Installation of Electronic Displays in Part 23 Airplanes
AC 23-15A Small Airplane Certification Compliance Program
AC 23-17A Systems and Equipment Guide for Certification of Part 23 Airplanes
AC 23-8B Flight Test Guide for Certification of Part 23 Airplanes
AC 43.13-1B Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair
AC 43.13-2A Acceptable Methods, Techniques, and Practices - Aircraft Alterations
AC 20-138A Airworthiness Approval of Global Navigation Satellite System (GNSS) Equipment
c. Other Applicable FAA and Industry Documents or Job Aids The FAA and Industry Guide to Product Certification, January 1999, located on the web at: http://www.faa.gov/certification/aircraft/av-info/dst/CPIGUIDE.pdf
The FAA and Industry Guide to Avionics Approvals, April 2001, available on the web at: http://www.faa.gov/certification/aircraft/AVCPIcov.pdf
GAMA Publication Number 10, Recommended Practices and Guidelines for Part 23 Cockpit/Flight Deck Design, available on the web at:
http://www.gama.aero/pubs/onlineCatalog.php 5
GAMA Publication No. 12 - Recommended Practices and Guidelines for an Integrated Cockpit/Flightdeck in a Part 23 Airplane, available on the web at:
http://www.gama.aero/pubs/onlineCatalog.php
3. What are common definitions for the terms used in this AC?
AD Airworthiness Directive AML Approved Model List CFR Code of Federal Regulations CPI Certification Process Improvement DER Designated Engineering Representative FHA Functional Hazard Assessment GAMA General Aviation Manufacturers Association GPS Global Positioning System ICA Instructions for Continued Airworthiness MFD Multi-Function Display PSCP Project Specific Certification Plan STC Supplemental Type Certificate TC Type Certificate TCDS Type Certificate Data Sheet
4. What is an AML STC?
a. An AML STC is similar to a multimodel STC, which applies to multiple airplanes listed on the same TCDS. However, an AML STC goes one step further by allowing the STC to apply to several different TCs. This allows a single STC to address several different TCs by documenting the data and limits suitable to each of the several different aircraft. This is a more efficient use of resources compared to multiple single-model approvals for an installation that is similar or identical for several different models. See Order 8110.4B for more information on the STC process.
b. To keep track of the various models, an AML is created and attached to the STC (FAA form 8110-2). Whenever another model is added or a document is amended, the AML is changed and not the STC. This lessens the number of STC approvals and may be a more efficient use of resources compared to multiple single-model approvals.
However, any change to the AML requires FAA approval.
c. STC approvals with an AML have the same data requirements as an STC applicable to a single model of aircraft. However, when making avionics modifications it is possible to combine the current approval process with some of the advantages of the field approval process. Field approvals typically allow for data from a single STC to be reused for multiple approvals where similarity can be clearly shown. However, they are often carried out with little or no follow-on ACO involvement, which may only be suitable for simple installations where Part 43 “acceptable data” clearly addresses differences between the existing approval and the follow-on installation. The AML provides an advantage, since ACO engineering involvement is required for each 6
installation on each model on the AML and differences are evaluated and documented clearly in the installation instructions.
d. For more complex avionics installations (See Chapter 1, Section 6.c), it may be more suitable for the applicant to address interface considerations to existing equipment upfront for each proposed model on an AML through a prototyping approach.
e. This process allows portions of the compliance data to be reused, and new showings of compliance for each model to be provided as needed. The AML process is meant to provide the proper measure of certification oversight, but also provide a streamlined approval process for part 23 avionics. Further guidance on the STC process is available in AC 21-40.
5. What does existing guidance say about AML STC approvals?
a. Order 8110.4B, section 4-2a(4), clearly provides for a single STC data package to be used for multiple airplane models, provided the following conditions are met:
(1) The STC data package consists of a principal design and certification data package for the change and either a master installation package for all eligible type certificated products or a separate installation package for each eligible type certificated product.
(2) Any design or installation differences between eligible products are identified in the design and installation data.
(3) Installation complexity is similar on all eligible products.
(4) The change does not require a large reevaluation of the type-certificated product's airworthiness.
(5) Either the flight or operational characteristics, or both, of the type-certificated product remain unchanged.
(6) The change does not create an acoustical change to the type-certificated product (See §21.93 and FAR Part 36 to define an acoustical change).
(7) The eligible type certificated products, applicable FAA approved documents, and the certification basis for each model are listed on a special page known as the “Approved Model List (AML)” attached to the STC under the following conditions:
(a) Whenever a type certificated product is added or one of the FAA approved documents is amended, deleted, or added, the AML itself is amended and approved by the FAA, not the STC.
(b) An AD is required to remove a product from an AML in the case where some unsafe condition exists unless the STC holder can prove no installation was made.
The applicant should always coordinate with the responsible ACO to determine the best course of action for removing a model from the AML using existing FAA process.
Existing installations may be affected if the ACO determines that an unsafe condition exists for a particular model, which may require the removal of the equipment in question.
(c) An STC with an AML can be transferred in total to another holder but cannot be split into more than one STC.
b. The “Industry and FAA Avionics Approval Guide” states that, for avionics equipment with similar installation requirements on several aircraft models, a generic approach to the approval process should be considered. The goal of the generic STC approval process is to develop installation instructions that can be used to install avionics equipment in several different aircraft models. These installation instructions will not repeat complete STC programs and will allow the reuse of compliance data where suitable. Title 14 CFR, part 21, § 21.101, also supports this idea.
c. This AML STC approach can reduce the effort for follow-on approvals the avionics installers must get and should reduce the number of field approvals that are performed. It will streamline the STC approval process and allow multiple models to be approved at once. However, there has been some confusion of defining “type design” in discussions about this generic approval process. This guidance seeks to clarify that a single compliance data package is suitable for AML approvals if applicability of the data package to different models and likeness between type designs can be clearly shown and documented. By identifying installation requirements up front, the AML STC process simplifies the approval of installation data for other models.
6. What avionics can be approved under the AML STC process?
a. Critical and noncritical avionics system installations can be addressed using the AML process, provided the ACO and applicant agree the process will adequately address the certification requirements for a given system, and its installation on other model aircraft. The term ”critical'' refers to those functions identified by a (§ 23.1309) hazard analysis whose failure would contribute to, or cause, a failure condition that would prevent the continued safe flight and landing of the airplane. AML STC approvals can be separated into two classifications, simple or complex, depending on the system installation complexity.
b. A simple system is defined as a stand-alone equipment installation that 1) has well understood requirements for power, antenna, and other interfaces, and 2) does not require substantial model specific configuration settings to be applied. A simple AML STC involves an installation that is repeated easily for all the airplanes listed on the AML using a generic set of installation instructions and a generic configuration setting.
However, before using a generic set of installation instructions, the applicant must clearly document and show similarity between the aircraft on the AML. Further compliance findings and formal conformity inspections may not be required after an initial showing 8
of compliance to §21.33 for simple systems if similarity is clearly documented for every model on the AML. The ACO and applicant must agree on this approach, and it must be documented in the Certification Plan and the Model Qualification Process. This approach is clearly recommended in existing guidance for stand-alone GPS receivers in AC 20-138A and should also be applicable to radios, horizontal situation indicators, course deviation indicators, and other typical avionics components.
c. Complex systems are defined as systems that require model specific interface or installation configuration changes or as single or multiple component systems that require significant data communication and integration with existing equipment, or both.
A complex AML STC may involve either an installation where similarity is not as easily shown between models or where the modification requires model specific changes for each airplane on the AML, or both. This may be handled by using model specific installation instructions added as an appendix to the generic set of instructions, or by separate model specific installation instructions clearly referenced on the AML. The applicant should “prototype” the system installation as each model is added to the AML to ensure that model specific requirements are addressed and integrated into the installation instructions. For complex installations, specific compliance and conformity inspections are necessary using model specific information in the installation instructions to comply with §21.33.
d. Complex AML STC approvals should be handled more like multimodel STC approvals, and require model specific documentation for each model listed on the AML.
For example, it may be necessary to produce a model specific System Safety Assessment for each model on the AML to satisfy §23.1309 for complex systems. It may be possible to use one set of §23.1309 compliance data for simple systems.
e. Regardless of the equipment being approved, the AML STC installation instructions must be detailed to allow multiple model installations. This should reduce the number of deviations from the STC data package that are sought for follow-on installations. The idea is to reduce the number of cases where maintenance data, accepted under part 43 rules, is used to support an installation when the STC data package either 1) does not correspond to the airplane, 2) does not address a particular interface, or 3) is incomplete. This may require more work up front for the applicant, but should reduce the number of problems for future installations.
7. What are some limits of the AML STC process?
a. The AML STC process is subject to the same guidelines and limits discussed in Order 8110.4B and 14 CFR, part 21, Subpart E. Therefore, it may not be suitable for new and novel features. The applicant and the ACO should coordinate on each specific certification project to determine if the AML process is applicable. The Small Airplane 9
Directorate should be involved in determining when an AML is applicable in cases where new and novel features are present through the Certification Project Notification (CPN) process according to Order 8110.4B.
b. Order 8110.4B states that if an applicant presents a foreign registered airplane as an article for inspection or test under any STC approval, the applicant must provide evidence the civil aviation authority of the State of Registration agrees to the modification to the airplane. This also applies to AML approvals.
c. The AML STC process should not be applied to those systems whose installation configuration varies significantly among various serial number aircraft of the same model, or those systems that can directly control the aircraft. For example, an AML STC would not be suitable for autopilot installations. For autopilot installations, there may be serial number specific airplane-rigging problems that have to be taken care of on a caseby-case basis. Another example would be a Reduced Vertical Separation Minimum (RVSM) STC approval where model and serial number specific static pressure system characteristics could preclude a generic approach to the certification project. There are cases where the static source error correction curve for RVSM approval is only applicable to a single serial number airplane. The part 91 RVSM guidance material contains details on group approval methods for RVSM approval.
d. High Intensity Radiated Fields (HIRF) and lightning compliance, as well as assumptions made during the Functional Hazard Analysis (FHA) and System Safety Assessment (SSA) for a particular system, may limit the use of the AML process since these items can be model dependent. The applicant and the ACO must agree on a process to allow these items to be addressed in a generic manner for the models on the AML, and agree on Continued Airworthiness procedures to maintain compliance for these items.
e. Deviations from the original approval to allow an installation on a particular model listed on the AML will require the installation instructions to be modified. The approval can also be completed under an individual STC, depending on the scope of the deviation. Existing processes in FAA Order 8300.10 must be used to determine when a deviation to the AML STC is necessary. A deviation is necessary when the installation does not match the equipment list and/or equipment integration approved in the original installation. Any deviations from the original STC must be documented and approved either by an ACO engineer, a DER, or the field inspector. The AML process is not meant to be a blanket approval that delegates the integration of additional equipment to the installer without FAA involvement.
CHAPTER 3. AML STC PROCESS
1. What are the key process steps to an AML STC?
a. The AML STC process is similar to other STC processes, with added steps to allow the requirements for the approval to span across type data sheets. Avionics installation approvals should follow the requirements in 14 CFR, part 21, subpart E, the guidance in Order 8110.4B, and the “Industry Guide to Avionics Approvals,” with the guidance in this AC. Figure 1, on the next page, shows a generalized flowchart for the AML process. For AML STC projects, the applicant is expected to submit a Project Specific Certification Plan (PSCP), following the CPI Process.
b. It is important for the applicant and the responsible ACO to coordinate at the start of the program to document properly the AML process in the PSCP or other FAA approved Certification Plan, which should include:
(1) Development of a Model Qualification Process (see Chapter 3, Section 3)
(2) Development of AML amendment procedures (see Chapter 3, Section 4)
(3) Agreement on data package requirements (see Chapter 4).
2. How is the AML created?
a. Eligibility for each model on the AML must be clearly documented by the applicant. For simple systems, it may be easier to prove similarity or identicality. For complex systems, the applicant may need to “prototype” the system installation as each model is added to the AML. This will ensure that model specific requirements have been addressed and integrated into model specific sections in the installation instructions and other documentation.
b. An applicant cannot simply apply engineering judgment to create the AML, but the applicant must document a repeatable decision process to include each model on the AML and the methods used to determine applicability. Also, the assumptions and limits for the approval must be clearly stated to avoid confusion for future installations or amendments to the AML. For example, RTCA/DO-160 environmental qualification performed during design approval for a particular operating environment on one model may not be suitable for other models being proposed for addition to the AML. Also, assumptions made during the FHA may limit which models can qualify for addition to the AML.
Standard Avionics Certification Process Product Proposed for Certification AML STC?
Develop/Submit PSCP NO YES Installation Complete & Cert Testing Complete
FAA ACO Issues Certificate Coordinate Model Qualification Process, AML Amendment Process, & AML Data Pkg Requirements with ACO Standard Avionics Certification Process Generate/Amend Model List & Issue 8110-3 Develop/Submit
AML PSCP Develop/Amend Installation Instructions End of Project New Models or Other Changes?
NO YES Installation Complete & Cert Testing Complete
FAA ACO Issues Certificate or AML
Figure 1 – General Process AML STC Approvals 12
c. It may necessary for an applicant to split an AML into sections to separate models into groups where similarity can be clearly shown. They may be split according to operational capabilities, certification basis, airplane classification under AC 23.1309, or by other model characteristics that can be clearly grouped. This would allow installation considerations for each group to be addressed separately.
d. The AML should contain a list of the most recent STC documentation to track revisions and changes as the AML is amended. It may be necessary for eligibility for each model on the AML to be revisited if a major change is made to an existing AML approval, such as a change to system design or intended function.
3. What is the Model Qualification Process?
a. The Model Qualification Process is a procedure, agreed on by the ACO and the applicant, that is used by the STC holder to capture specific engineering decisions, design attributes, limitations, and assumptions made during the system development or Technical Standard Order (TSO)/design approval. This helps standardize the AML STC approval process by formally documenting the engineering analysis used to determine applicability and eligibility of a given model for the AML STC.
b. The Model Qualification Process should capture assumptions made during the design phase of a particular piece of equipment and may preclude a model from being included on the AML because of these assumptions. For example, a decision by the equipment manufacturer to develop system software to current revision of RTCA/DO- 178 Level C for critical functions may limit the installation eligibility. According to AC 23.1309-1C, Figure 2, by only certifying to software level C for critical functions, installations for part 23 aircraft over 6,000 pounds are not acceptable and require a higher software development level. See Appendix 1 for more information.
c. The Model Qualification Process requires detailed foreknowledge of the system and the models proposed for the AML. The data submitted with the AML should include information showing the Model Qualification Process has been specifically applied to each model on the AML to verify applicability. The submittal should also include a form 8110-3 that approves the Model Qualification data package and recommends approval of the AML. The 8110.3 should include a clarifying note stating, "This approval is for engineering design data only and is not an installation approval," according to Order 8110.37C. The 8110-3 should reference applicable Part 23 requirements that could influence applicability for models on the proposed AML, given the design assumptions for the equipment being installed. Examples include §23.1301, §23.1309, and §23.1353.
More detail on data package requirements is available in Chapter 4.
d. The Model Qualification Process should evaluate each model on the AML to verify the assumptions used during HIRF and lightning compliance, and during the System Safety Assessment, are valid. These items can be installation dependent, so a formal process must be in place to make sure compliance data is applicable to each model proposed for the AML and that common installation and wiring practices are adhered to.
The applicant and the ACO must agree on a process to allow these items to be addressed in a generic manner for the models on the AML, and agree on Continued Airworthiness procedures to maintain compliance for these items.
e. More information on this process may be found in Chapter 5, “Model Qualification Process Requirements.”
4. How is an avionics AML STC amended?
a. Changes that affect the original basic system approval must be addressed as an amendment to the STC itself and may require further showing of compliance. For example, changing the intended function of a box by installing modified software would require an amendment to the STC itself and may also influence what models can be on the AML. Another example would be a change to the way the equipment is installed that could influence system functionality or the certification assumptions made during the original approval.
b. When an AML STC is amended to add a model, the documentation associated with the AML is amended and not the STC itself. The responsible ACO and the applicant must agree on the procedures to amend the AML; however, the following is a list of the basic steps involved.
(1) The applicant proposes a model to be added to the AML.
(2) The applicant subjects the proposed model to the Model Qualification Process.
(3) The applicant modifies installation instructions, and other documents, as needed to accommodate the new model.
(4) The applicant submits a data package and a form 8110-3 documenting the applicability of the STC to the model in question and recommending approval to add the model to the AML. According to Order 8110.37C, form 8110-3 should contain a clarifying note stating, "This approval is for engineering design data only and is not an installation approval.”
(5) The FAA reviews the submittal and amends the AML.
(6) The FAA issues the new AML with the new model added.
c. Changes to or approval of the AML is not delegated to a DER since this would allow new models to be added to the AML (new STC approvals) without FAA oversight.
A Designated Alteration Station (DAS) with authorized privileges may amend an AML for which it holds an STC if the data package and other STC documentation discussed above is submitted for FAA review according to the existing DAS agreement for STC approvals.
d. As mentioned in Order 8110.4B, an AD must be issued to remove a model from an AML. See Chapter 2, Section 5.a.(7).b.