AC 21-46A

Advisory circular · Technical Standard Order Program

Approved
February 23, 2017
Last reviewed
March 14, 2017
Cancels
AC21-46
Family
AC 21-46 · 2 versions
Revision
A
14 CFR parts
21

Guidance, not mandatory unless a rule or AD requires it. DRS record last changed October 23, 2026.

Show pages 6–17

3-9

3.12 Roles of the FAA and Applicant.

We coordinate between the ACO and the Manufacturing Inspection District Office (MIDO) to help you, the applicant, produce TSO articles according to the approved design. Approving a TSOA application requires the ACO to approve the design and the MIDO or Manufacturing Inspection Satellite Office (MISO) to approve the production system. A LODA is an FAA design approval only. Approving a LODA application requires the ACO to approve the design of the foreign-manufactured articles. The applicable CAA issues the corresponding production approval and oversees the production system. Figure 3-1 details the basic roles of the FAA and applicant in the TSO process.

3-10 Figure 3-1. Basic Roles of the FAA and Applicant in the TSO Process * Applicant AIR-100 ACO MIDO  Control the design and quality of the article  Show compliance with applicable TSO standard  Set up and maintain a QS that meets § 21.607 or is in accordance with bilateral agreement  Provide a statement of conformance to the applicable TSO(s)  Request approval to deviate from TSO  Establish and provide installation instructions, operational limitations, OPR summary, and maintenance instructions  Provide maintenance instructions and installation limitations to each person who receives articles, to ensure the article continues to meet the MPS of the TSO after installation  Mark each article according to § 45.15(b) and as specified in each applicable TSO  Report service difficulties pursuant to § 21.3  Submit TSOA’s minor changes to the ACO  Submit to the FAA document describing how its organization will ensure compliance  Develop PSP with ACO as applicable  Administer TSO program policy  Develop and issue new TSO  Determine when TSO require revisions  Cancel obsolete TSO  Determine if all TSOA for a particular TSO must be withdrawn, and publish intentions of withdrawal in the Federal Register before the withdrawal. If it is determined necessary, the process defined in the appropriate paragraph of Order 8150.1 will be followed  Grant/deny deviation requests not delegated to the ACO  Maintain records for TSO, including canceled TSO  Process TSOA applications and LODA applications from a CAA, if applicable  Recommend approval or denial of deviations to the TSO to AIR-100  Grant/deny deviations that Order 8150-1D or a specific TSO has delegated to the ACO  Coordinate with MIDO (TSOA) or follow the procedures defined in the bilateral agreement (LODA) before issuing TSOA/LODA letters.

 Witness various functions if deemed necessary (refer to § 21.610)  Find that the article design complies with the applicable TSO  Send applicant TSOA, LODA, or denial letter  Investigate reports of service difficulties and noncompliance  Submit enforcement reports when holders do not comply with part 21, subpart O  As applicable, work with applicants to develop Partnership for Safety Plans (PSP)

 Verify production system produces articles that conform to the approved design  Approve the quality system  Issue TSOA article production approval letter to ACO  Conduct surveillance at the TSOA holder’s and supplier’s facilities, both domestic and foreign, if appropriate.

 Investigate service difficulty reports and nonconformities.

 Submit enforcement reports when holders do not comply with part 21, subpart O

* Refer to applicable TSO and part 21, subpart O, for further details.

4-1 CHAPTER 4. TSOA AND LODA HOLDER RESPONSIBILITIES

4.1 Continue to Meet the Requirements of the TSO.

Pursuant to § 21.616, as the TSOA or LODA holder, you must:

Amend the document required by § 21.605 as necessary to reflect changes in the 4.1.1 organization and provide these amendments to the FAA;

Maintain a quality system in compliance with the data and procedures approved for the 4.1.2 TSO authorization;

Ensure that each manufactured article conforms to its approved design, is in a condition 4.1.3 for safe operation, and meets the applicable TSO;

Mark the TSO article for which an approval has been issued. Marking must be in 4.1.4 accordance with 14 CFR part 45, including any critical parts;

Identify any portion of the TSO article (e.g., sub-assemblies, component parts, or 4.1.5 replacement articles) that leave the manufacturer's facility as FAA approved with the manufacturer's part number and name, trademark, symbol, or other FAA approved manufacturer's identification;

Have access to design data necessary to determine conformity and airworthiness for 4.1.6 each article produced under the TSO authorization. The manufacturer must retain this data until it no longer manufactures the article. At that time, copies of the data must be sent to the FAA.

Retain the TSO authorization and make it available to the FAA upon request; and 4.1.7 Make available to the FAA information regarding all delegation of authority to 4.1.8 suppliers.

Other countries follow requirements of bilateral agreements, if applicable. 4.1.9

4.2 How to Mark Each Article.

Mark each article pursuant to § 21.616(d) and § 45.15(b), and as specified in the TSO.

Before you ship any article, you must determine that it conforms to its approved design 4.2.1 and mark it with all the information required by § 21.616(d), which includes the specific TSO for which the authorization was granted. You must also mark the article with all specific marking requirements as called out in the TSO for which authorization was issued and as described in paragraphs 4.2.4 and 4.2.5 of this AC. Be sure to review appendices in the TSO, as they may contain additions or exceptions to other marking requirements contained in a referenced industry document (such as Society of

4-2 Automotive Engineers (SAE) documents, aerospace standards (AS), or RTCA, Inc.

(RTCA) documents).

The marking must be permanent and legible. The marking must be accessible (without 4.2.2 the use of tools) in a location where it is easily readable and not easily erased or disfigured. If you receive information about your in-service articles that the TSO markings are missing or can no longer be read, you must investigate the cause and make any design changes necessary to resolve the issue.

When you believe an article is impractical to mark (for example, because of size or 4.2.3 space limitations), you must request a deviation, unless the specific TSO provides explicit alternative marking instructions.

Electronic part marking that identifies the article by electronically embedding the 4.2.4 identification within the hardware component itself (using software) may be used instead of marking the article on the equipment nameplate. If electronic marking is used, it must be readily accessible without the use of special tools or equipment.

Electronic marking of an article is acceptable when the information provided by an electronic identification query system is stored in non-volatile memory. The electronic identification system must be verifiable on board the aircraft, when the aircraft is on the ground at any geographic location, and must provide the specific information required by § 45.15. Ensure that the installation instructions include instructions and technical data needed to facilitate electronic part marking display on the aircraft.

Refer to paragraph 5.4 of this AC for further marking information on multiple TSO 4.2.5 articles.

Refer to paragraph 5.3 of this AC for further marking information on incomplete TSO 4.2.6 articles.

4.3 Report Service Difficulties Pursuant to § 21.3.

As a TSOA holder, you are required by § 21.3(b) to report to us any defect in your 4.3.1 article that you have determined could result in any of the occurrences listed in § 21.3(c). These occurrences include, but are not limited to:

Fires; 4.3.1.1 Engine exhaust system failures; 4.3.1.2 Toxic or noxious gases in the crew compartment or passenger cabin; 4.3.1.3 Malfunctions, failures, or defects in the propeller control system; 4.3.1.4 Flammable fluid leakage; 4.3.1.5 Structural or material brake system failures; 4.3.1.6

4-3 Malfunctions, failures, or defects in the flight control system including 4.3.1.7 interference with normal control; and Malfunctions or failures of attitude, airspeed, or altitude instruments. 4.3.1.8 Note: Review § 21.3(c) for the complete and accurate list of your responsibilities.

If we determine during an accident investigation or service difficulty that your article is 4.3.2 unsafe, you must report to us at our request any results you find or actions you plan to take to correct the deficiencies. You will also have to submit to us any data we need to help the FAA issue an airworthiness directive (pursuant to § 21.3).

4.4 Design Changes.

As a TSOA holder, you are responsible for any design changes you make to your article 4.4.1 and for updating the descriptive and substantiation data. Design changes to your article are classified as either minor or major. We require that you evaluate all design changes to determine if they are minor or major changes.

Pursuant to § 21.601, it is the responsibility of the TSOA holder or LODA holder to 4.4.2 control the design relative to the applicable TSO requirements, including all parts, processes, or services procured from an outside source. Similarly, it is the responsibility of the TC/STC holder to ensure the TSO articles that have undergone design changes continue to meet the applicable airworthiness requirements of the aircraft.

Minor Design Changes Under a TSOA. 4.4.3 We permit TSOA holders to make minor design changes to their articles without further approval. However, all minor design changes must be substantiated to show compliance with the applicable TSO MPS requirements (pursuant to § 21.619(a)). We encourage you to propose to your ACO what constitutes a minor change, including the changes made by your suppliers, for the particular TSO article being manufactured and work with your ACO to establish a mutually agreed upon process for managing minor design changes. Sometimes minor changes may require significant substantiation (including testing) to ensure the article still meets the TSO requirements. However, unless the change results in a “substantially complete investigation” to the TSO, it can be classified as minor pursuant to § 21.619(a). Note that a major/minor design change classification under § 21.619(a) or (b) is made at the article level relative to the TSO standard and should not be confused with a major/minor design change classification under § 21.93. Design change classifications under § 21.93 are made at the product level.

We encourage you to use a partnership for safety plan to formalize the 4.4.3.1 agreement discussed in 4.4.3.1 with your ACO. You can find more information on this process in the FAA and Industry Guide to Product

4-4 Certification. The manufacturer must maintain and submit to the FAA, on request, minor change substantiation data (pursuant to § 21.619(a)).

The article model and/or part number are used for configuration 4.4.3.2 management at the aircraft level. You should change the part number of any article where a minor change to a previously manufactured article may affect the interchangeability at the product level, the use or installation of the article, or the minimum performance standards specified in the TSO.

Update any associated documentation, such as the installation instructions, to identify the difference between the previous and new part number versions of the article.

Pursuant to § 21.619(a), you must substantiate and document all minor 4.4.3.3 design changes. You must notify your ACO within the timeframe agreed upon with them. We recommend the data be submitted before shipping any articles. This will prevent you from distributing potentially noncomplying articles in the event the ACO finds that a minor change claim is improperly substantiated. You must state in your minor change notification letter that the changed article complies with the TSO. This statement reaffirms your compliance with part 21, subpart O. You can send this letter to the ACO by email.

If we determine a minor design change submittal is not sufficiently or 4.4.3.4 properly substantiated, you must provide additional substantiation or other data as requested by your ACO. This could require you to retest the article to show compliance with the TSO standard. If, after review of the substantiation, the ACO determines that the article no longer meets the TSO MPS, you must immediately stop marking and shipping any changed articles and comply with the TSO requirements.

If we determine a minor design change is really a major design change, 4.4.3.5 as defined in § 21.619(b), you must immediately stop marking and shipping any changed articles and comply with the criteria for major design changes.

Major Design Changes Under a TSOA. As stated in § 21.619(b), the FAA requires a 4.4.4 new TSO application for all major design changes to TSO articles under a TSOA.

If the applicable TSO is revised while the application is being evaluated, 4.4.4.1 you should provide an OPR summary with functional impacts to applicants for installation approval of the article;

A sufficient description should be provided for proper assessment; 4.4.4.2 Any OPRs with potential safety impact should be corrected; 4.4.4.3 OPR information should be provided in the installation manual or 4.4.4.4 supplemental data;

4-5 There should be a means for updating OPR summary if necessary; 4.4.4.5 The TSOA holder should provide contact information in case installer 4.4.4.6 needs more information; and The TSOA holder should have a means to accept problems reported from 4.4.4.7 the field.

Only need to demonstrate compliance with the TSO in effect at the time of 4.4.4.8 the original application, not the revised TSO.

The ACO can give up to a 6 month relief period to applicants with 4.4.4.9 pending applications provided the specific TSO being applied for contains provisions for doing so. If the applicant does not submit a complete application within this time, it must comply with the most recent TSO version.

Note: Some revised TSOs may contain a statement that the older version of the TSO will remain effective for a period of months after a revision becomes effective. During this time, the ACO may accept applications for either version of the TSO.

Design Changes Under a LODA. 4.4.5 Design changes to articles that have been issued a LODA are subject to the requirements defined in the applicable bilateral agreement. Generally, when the CAA considers a design change minor, it is approved without any FAA involvement. Design changes the CAA considers major require the LODA holder to apply for a new LODA.

Design Change by a Person Other Than the Manufacturer - TSOA and LODA. 4.4.6 Pursuant to § 21.619(c), we permit design changes to a TSO article by a person other than the original manufacturer who holds the TSO authorization, such as the product operator, the installer of the article, or the maintenance personnel. If the person seeking approval is another article manufacturer (refer to § 21.601(b)(5)), they must apply under a separate TSOA or LODA and obtain approval before modifying the article. The article may also be altered as part of an installation in an aircraft or engine, and approved under part 43 or the applicable airworthiness regulations in 14 CFR parts 23, 25, 27, 29, 31, 33, and 35. In all cases, the article must be permanently marked to indicate it has been modified.

The determination of whether a design change, repair, or alteration is major or minor 4.4.7 varies, and depends on which FAA approval is being affected. These changes are classified differently within their specific regulatory basis, and this classification depends on whether the FAA approval is a TSOA, STC, repair, or alteration. Minor changes under a TSOA may be a major change for other types of FAA approval and vice versa. Regardless of the classification of the modification, all modifications must be substantiated relative to the applicable requirements (pursuant to § 21.619).

4-6

4.5 Transferability.

As stated in § 21.614, the holder of a TSO authorization or letter of TSO design approval may not transfer the TSO authorization or letter of TSO design approval.

However, they may submit a request to the FAA for a transfer. The term “transfer” applies only to the TSO design approval. The production approval process that the MIDO accomplishes during a transfer is the same process for a new applicant or an applicant that is adding additional capability to an existing facility. TSOA transfer requests must be made by the current holder of the TSO authorization or letter of TSO design approval.

Examples of a Transfer. 4.5.1 When the sale or liquidation of a company that holds TSOA or LODA causes a change in the company’s legal status, those TSOA or LODA must be transferred. TSOA or LODA design data may be sold from one company to another, and this is also considered a transfer.

For example, the acquisition of a company with a TSOA or LODA by a 4.5.1.1 holding company would require a transfer of the TSOA or LODA if the acquired company is disbanded or absorbed into the purchasing company.

In this case, the legal entity that received the TSOA or LODA will no longer exist, so the original holder would be required to request a transfer of the TSOA to the purchasing corporation before being disbanded or absorbed. A company can transfer a TSOA or LODA only when we grant them an exemption to § 21.614.

As another example, assume XYZ Company holds a TSOA, and 4.5.1.2 ABC Corporation purchases XYZ Company. ABC Corporation plans to disband and absorb XYZ Company. In this case the legal status of XYZ has changed (for example, the company no longer exists as a legal entity) and the acquisition of the XYZ Company would necessitate a transfer of the TSOA or LODA.

Example of What Is Not a Transfer. 4.5.2 A company changing its name or relocating its facilities does not 4.5.2.1 necessitate the TSOA or LODA to be transferred. The acquisition of a company with a TSOA or LODA by a holding company would not necessitate the transfer of the TSOA or LODA if the acquired company continues to exist as the same legal entity to which the original TSOA or LODA was issued under the following conditions:

4.5.2.1.1 The acquired company retains possession of the TSOA or LODA, substantiating data, and responsibilities under the original authorization or approval; and

4.5.2.1.2 The acquired company retains the same quality system (TSOA only).

4-7 Example: ABC Corporation purchases XYZ Company. XYZ Company 4.5.2.2 holds a TSOA and will continue to operate under the same name, in the same location, with the same management, and under the same production system. In this case the legal status of XYZ has not changed and therefore the TSOA is not transferred.

Articles Approved With a TSOA. 4.5.3 Pursuant § 21.614, if you are changing your name, relocating your facilities, or being acquired by another company, you must inform your ACO before the action occurs, and you:

Should expect your ACO to forward this information immediately to your 4.5.3.1 MIDO/MISO;

Must not ship any articles from a new facility until the MIDO has 4.5.3.2 inspected and approved the new facility, and the ACO has reissued your TSOA; and Should expect your ACO to reissue the TSOA at the same level as the 4.5.3.3 original TSO after the MIDO determines your QS meets the requirements of § 21.137 pursuant to § 21.607 and you can produce each article to conform to your approved design.

Articles Approved With a LODA. 4.5.4 Pursuant to § 21.621, if you are a foreign manufacturer who holds a LODA and you are changing your name, relocating facilities, or being acquired by another company, you:

Must ensure your CAA provides the FAA written confirmation that your 4.5.4.1 legal status remains unchanged after an acquisition;

Must not mark or ship any articles with the TSO marking until the FAA 4.5.4.2 has reissued the LODA for name changes or facility relocations; and Should expect the FAA to reissue the LODA at the same level as the 4.5.4.3 original TSO after receiving written confirmation from the CAA that your article meets the TSO after a name change or facility relocation.

Converting a TSOA to a LODA. 4.5.5 Our regulations do not contain a provision for a manufacturer currently holding a TSOA to become a foreign manufacturer by relocating its design and production facilities outside the United States. In this case, your foreign facility should apply for a separate LODA as described in this AC. As the design approval holder (DAH) for the original TSOA, you will retain continued operational safety (COS) responsibilities.

Converting a LODA to a TSOA. 4.5.6

4-8 Our regulations do not contain a provision for a foreign manufacturer holding a LODA and wanting to become a U.S. manufacturer by relocating its design and production facilities into the United States. In this case, the manufacturer’s facility in the United States should apply for a new TSOA as described in this AC, applying for the current version of the applicable TSO(s). As the DAH for the original LODA, you will continue to have COS responsibilities.

5-1 CHAPTER 5. ADDITIONAL TSO TOPICS

5.1 Receiving a Parts Manufacturer Approval (PMA) to Modify a TSOA Article.

We do not issue PMA to modify TSO articles; we issue PMA to modify products (aircraft, engines, and propellers). PMA approves replacement and modification articles for specific type-certificated products. These articles may reside in an assembly approved under a TSOA on these specific products, but the PMA limits installation of these articles to those specific products. PMA cannot approve replacement articles solely for original articles approved solely under a TSOA.

5.2 Shipping a Subcomponent of an Article Independent of the Complete Article.

You can ship a subcomponent of an article independent of the complete article, but you must complete an FAA Form 8130-3, Airworthiness Approval Tag, or other acceptable document. This tag will help make clear that the subcomponent is only a piece of an article and to clarify the article in which it is intended to be installed.

5.3 Incomplete TSO Article.

An incomplete TSO article is one that provides only part of the performance and/or functionality specified in the applicable TSO. For us to approve and issue a TSOA or LODA for an incomplete TSO article, all of the following conditions must be met:

The incomplete article provides a major and independent TSO function. There must be 5.3.1 TSO requirement(s) that are specific to the function provided by the incomplete article (that is, in addition to general requirements related to software or environmental qualification).

Example of an incomplete article that provides a major and independent 5.3.1.1 function: TSO-C4, Bank and Pitch Instruments, contains requirements that apply to an electronic flight instrument system (EFIS). The EFIS displays “bank and pitch” information, but does not include a vertical gyro.

Because the EFIS provides a major independent TSO-C4 function that meets specific TSO requirements pertaining to a display, you may be granted an incomplete TSOA to TSO-C4.

Example of an incomplete article that does not provide a major and 5.3.1.2 independent function: a cooling fan for a global positioning system (GPS) covered by TSO-C196b, Airborne Supplemental Navigation Sensors for the Global Positioning System (GPS) Equipment using Aircraft-Based Augmentation. Because the cooling fan does not provide a major contribution of the TSO-C196b function, it is not eligible to be qualified as an incomplete TSO article.

5-2 The TSO MPS provides appropriate and adequate standards for evaluation of the article 5.3.2 as an incomplete article. You must identify and meet all the specific performance standards in the TSO that apply to the incomplete article (pursuant to § 21.603(a)(1)).

In the installation drawings and/or installation manual, you must adequately document 5.3.3 detailed instructions and limitations, pursuant to § 21.50 and § 43.13, for the installation and use of the incomplete article. For example, company “ABC” manufactures under TSO-C119c, Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment, TCAS II with Optional Hybrid Surveillance, a traffic alert and collision avoidance system (TCAS) antenna with an interface that is interoperable with a Company “XYZ” Model “123” TCAS computer. The installer must substantiate the interoperability between these two components when showing compliance with the applicable airworthiness requirements.

You must list in the installation manual the specific MPS that your article meets. This 5.3.4 should be provided by referencing the specific paragraphs of the TSO (a single reference can frequently be used to include a parent paragraph and all of its subparagraphs). This information will assist the installer of the TSO article in knowing the limitations of the article’s capabilities, to comply with § 21.50.

When not obvious from the component, you should permanently and legibly mark the 5.3.5 article with at least “INCOMP” adjacent to the TSO number marking (for example, “Meets TSOC69c INCOMP”) and include detailed instructions in the installation drawings or installation manual. Marking an article “INCOMP” or “Incomplete” will eliminate ambiguity about the article’s level of compliance.

5.4 Multiple TSO Authorizations for the Same Article.

If you elect to apply for a TSO Authorization, you must apply for all applicable TSO pertinent to the functions your article provides. You also need to request a deviation from § 21.15(b) to establish one TSO as the primary TSO to mark the article having multiple TSO approval.

Marking. 5.4.1 After having TSOA and the deviation approval, you can:

Mark the primary TSO number on the nameplate (marking each individual 5.4.1.1 TSO number on the article’s nameplate may be impractical).

Mark the primary article permanently and legibly with a statement that the 5.4.1.2 remaining TSO marking requirements are in the installation manual (IM),

(e.g., “See Inst Mnl for Addtl TSO approvals and/or markings.”).

List the other TSOs (and marking requirements for each TSO) in the front 5.4.1.3 section of the IM for the article’s primary TSO.