Required Design Changes

FAR 21.99 — Required Design Changes

FAR 21.99 explains how type certificate holders must submit design changes when an Airworthiness Directive is issued and share data with operators.

In Plain English

FAR 21.99 spells out what the type certificate (TC) holder — typically the aircraft or engine manufacturer — must do when the FAA identifies a safety problem with a certificated product.

There are two scenarios:

Unsafe condition (AD issued): When the FAA issues an Airworthiness Directive (AD) under Part 39 and decides design changes are needed to fix the unsafe condition, the TC holder must:
- Submit appropriate design changes for FAA approval upon request, and
- Once approved, make the descriptive data available to all operators of products previously certificated under that TC.
No current unsafe condition: If service experience shows that a design change would simply improve safety (no AD required), the TC holder may submit the change for approval. Once approved, the manufacturer must share the design change information with all operators of that product.

Why it matters: this rule is the link between continued airworthiness and the fleet you fly. It ensures fixes don't stay locked inside the manufacturer — they flow out to every operator so the entire fleet benefits from safety improvements.

Regulation Text

14 CFR § 21.99

§ 21.99 Required design changes. (a) When an Airworthiness Directive is issued under Part 39 the holder of the type certificate for the product concerned must— (1) If the FAA finds that design changes are necessary to correct the unsafe condition of the product, and upon his request, submit appropriate design changes for approval; and (2) Upon approval of the design changes, make available the descriptive data covering the changes to all operators of products previously certificated under the type certificate. (b) In a case where there are no current unsafe conditions, but the FAA or the holder of the type certificate finds through service experience that changes in type design will contribute to the safety of the product, the holder of the type certificate may submit appropriate design changes for approval. Upon approval of the changes, the manufacturer must make information on the design changes available to all operators of the same type of product. [Doc. No. 5085, 29 FR 14567, Oct. 24, 1964, as amended by Amdt. 21-3, 30 FR 8826, July 24, 1965]

Oral Exam Questions a DPE Might Ask

Q1When the FAA issues an Airworthiness Directive, what is the type certificate holder required to do?

Per FAR 21.99(a), if the FAA finds design changes are necessary to correct the unsafe condition, the TC holder must submit appropriate design changes for approval upon FAA request, and then make the descriptive data available to all operators of previously certificated products.

Q2If there is no unsafe condition, can a manufacturer still submit a design change for approval?

Yes. Under FAR 21.99(b), if service experience shows a change would contribute to safety, the TC holder may voluntarily submit design changes for approval, and once approved must share the information with all operators of that product.

Q3Who is responsible under FAR 21.99 for distributing approved design change information to operators?

FAR 21.99 places that responsibility on the **type certificate holder/manufacturer**, who must make the descriptive data or design change information available to all operators of the affected product once the changes are FAA-approved.

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Related Sections in Part 21

§ 21.1

Certification Procedures

§ 21.101

Type Certificate Changes