FAR 21.619 — TSO Design Changes
FAR 21.619 explains how TSO article manufacturers handle minor vs. major design changes, model designations, and approval paths under Part 21.
In Plain English
FAR 21.619 governs how a manufacturer holding a TSO authorization can change the design of an approved article (a part or appliance). The rule splits changes into two categories and limits who can make them.
- Minor changes (anything that isn't major): The manufacturer can make them without further FAA approval. The article keeps its original model number (part numbers may be used to track the minor change), but the manufacturer must send the FAA any revised data needed to show continued compliance with § 21.603(a).
- Major changes: Any change extensive enough to require a substantially complete investigation to verify TSO compliance. Before making a major change, the manufacturer must assign a new type or model designation and apply for a new TSO authorization under § 21.603.
- Non-manufacturer changes: Anyone other than the original manufacturer who wants to change the design must either become a manufacturer and apply for their own separate TSO authorization, or seek approval under Part 43 or the applicable airworthiness rules.
Operationally, this matters because TSO articles installed on aircraft must remain traceable and compliant. Knowing which path a change takes prevents installing unapproved parts.
Regulation Text
14 CFR § 21.619§ 21.619 Design changes.
(a)The manufacturer of an article under an authorization issued under this part may make minor design changes (any change other than a major change) without further approval by the FAA. In this case, the changed article keeps the original model number (part numbers may be used to identify minor changes) and the manufacturer must forward to the FAA, any revised data that are necessary for compliance with § 21.603(a).
(b)Any design change by the manufacturer extensive enough to require a substantially complete investigation to determine compliance with a TSO is a major change. Before making a major change, the manufacturer must assign a new type or model designation to the article and apply for an authorization under § 21.603.
(c)No design change by any person (other than the manufacturer who provided the statement of conformance for the article) is eligible for approval under this part unless the person seeking the approval is a manufacturer and applies under § 21.603(a) for a separate TSO authorization. Persons other than a manufacturer may obtain approval for design changes under part 43 or under the applicable airworthiness regulations of this chapter.
[Docket No. FAA-2006-25877, Amdt. 21-92, 74 FR 53392, Oct. 16, 2009, as amended by Doc. No. FAA-2018-0119, Amdt. 21-101, 83 FR 9169, Mar. 5, 2018; Doc. No. FAA-2022-1355, Amdt. 21-106, 87 FR 75710, Dec. 9, 2022]
Oral Exam Questions a DPE Might Ask
Q1What's the difference between a minor and a major design change to a TSO article?
Per FAR 21.619, a major change is one extensive enough to require a substantially complete investigation to determine TSO compliance; anything else is a minor change that the manufacturer can make without further FAA approval.
Q2If a TSO article manufacturer makes a major design change, what must they do before producing the changed article?
Under FAR 21.619(b), they must assign a new type or model designation to the article and apply for a new TSO authorization under § 21.603.
Q3Can someone other than the original TSO manufacturer get a design change approved under Part 21?
Not under Part 21 unless they themselves are a manufacturer applying for a separate TSO authorization under § 21.603(a). Otherwise, FAR 21.619(c) directs them to seek approval under Part 43 or the applicable airworthiness regulations.
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Related Sections in Part 21