Substitute Technical Standard Order (TSO) Aircraft Equipment

AC 20-41A · FAA

Public domain · FAAAdvisory Circulars

Overview

The Substitute Technical Standard Order (TSO) Aircraft Equipment (AC 20-41A) is a public-domain FAA advisory circular, republished here as a free chaptered HTML edition with a linked table of contents and the official PDF.

Publisher: FAA
Document: AC 20-41A
Pages: 2

Key points

This advisory circular outlines acceptable means for substituting Technical Standard Order (TSO) equipment in aircraft installations.
Substitutions of TSO-approved equipment for functionally similar TSO'd equipment may not require a flight check if certain conditions are met.
Ground functional tests, analyses, and descriptive data must demonstrate that the substitute equipment meets applicable airworthiness regulations.
Substitution procedures do not apply to equipment that directly affects flight controls or flight characteristics, such as autopilots and flight directors.
Flight tests may be required to evaluate the effects of changes, as determined by the approving authority.

Frequently asked questions

What is the purpose of this advisory circular?

The purpose of this circular is to set forth an acceptable means for complying with rules governing aircraft equipment installations when substituting TSO equipment.

What regulations are referenced in this document?

The document references Parts 23, 25, 27, and 29, as well as sections 21.95, 21.113, 21.115, and 43.13 of the Federal Aviation Regulations.

What types of equipment are excluded from the substitution procedures?

The substitution procedures should not be used for auto pilots, flight directors, inertial navigation systems, stability augmentation systems, stall prevention systems, tires, wheel-brake systems, or any equipment affecting flight controls.

What must be included in the FAA approved Flight Manual?

Any significant change in equipment capability determined from the evaluation of the substitution must be included in the appropriate part of the FAA approved Flight Manual.

Who decides if flight tests are necessary for evaluating changes?

The decision to conduct flight tests rests with the approving authority.

Document

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M~Y-J,J//ADVISORY

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,.;u:v.i•:; CIRCULAR

DEPARTMENT OF TRANSPORTATION

FEDERAL AVIATION ADMINISTRATION

SUBJECT: SUB.5TITUTE TECHNICAL STANDARD ORDER (TSO) AIRCRAFr EQUIPMENT

1. PURPOSE. This circular sets forth an acceptable means for complying with the rules governing aircraft equipment installations in cases involving the substitution of technical standard order (TSO) equipment for functionally similar TSO approved equipment.

2. CANCELLATION. AC 20-41, dated August 30, 1965, is cancelled.

3. REFERENCE REGULATIONS. Parts 23, 25, 27, and 29, and sections 21.95, 21.113, 21.115, and 43.13 of the Federal Aviation Regulations.

4. BACKGROUND. Under the referenced rules, the determination of compliance with the regulations may require that an aircraft be flown for functional check of any replacement parts or installations. There have been dis cussions relative to the possibility of substantiating the acceptability of installations, without a flight check, when functionally similar TSO'd equipment is substituted for previously approved TSO'd equipment. The acceptable means of compliance :i.n paragraph 5 deals with this question and is applicable to the evaluation of replacements under the alterations performance rules of section 43.13, a minor change in type design per section 21@95, or supplemental type certificate procedures of sections 21.113 and 21.115.

5. ACCEPTABLE MEANS OF CCMPLIANCE. In the case of an aircraft alteration involving the substitution of TSO-approved equipment for functionally similar TSO'd equipment, an acceptable means of compliance with applicable airworthiness regulation~without the aircraft being flight checked, is to: a. Show, by means of ground functional tests, analyses, drawings, descriptive data or combination of these that: (1) The substitute equipment anq its installation meet the airworthiness regulations which are applicable to the equipment to be replaced; Initiated by: AFS-130 AC 20-41A 4/5/77 (2) The connections (electrical, electronic, mechanical, or fluid) between the equipment under consideration and other equipment in the aircraft either remain the same 0r, if these connections are modified, the modification does not affect the TSO status of the equipment; and (3) The radiation system (including transmission lines) and other electrical or electronic aircraft equipment that connect to the equipment under consideration either remain the same, or if modified, the modification does not adversely affect the per formance of such systems or equipment and the subject equipment.

b. Include necessary information in the appropriate part of the Federal Aviation Administration approved Flight Manual concerning any signif icant change in equipment capability as determined from the evaluation outlined in items 5.a.

6. EXCLUDED EQUIPMENT. The substitution procedures provided by this circular should not be used in connection with auto pilots, flight directors, iner tial navigation systems, stability augmentation systems, stall prevention systems, tires, wheel-brake systems, or any other equipment directly affecting flight controls or flight characteristics. Substitutions which affect equipment in the cockpit should be evaluated by appropriate flight test personnel.

7. FLIGHT TESTS. Flight tests may be necessary, in some cases, to adequately evaluate the effects of changes and this decision rests with the approving authority.

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Director, Flight Standards Service Page 2 Par 5 DEPART~fENT OF TRANSPORTATION FEDERAL AVIATION AD1\1INISTRATION POS'l AGE AND l!'EES PAID Washington, D.C. 20591 FEDERAL AVIATION ADl!INISTRATIOX Officinl BusinesA U.S.MAIL DOT 515 PENALTY FOR PRIVATE USE, $300 FIRST CLASS