FAR 21.31 — Type Design
FAR 21.31 defines what a type design includes: drawings, specs, materials, airworthiness limitations, and data needed to certify aircraft configuration.
In Plain English
FAR 21.31 spells out exactly what an aircraft's type design must include. The type design is the official package of information that defines a certified product (aircraft, engine, or propeller) and proves it meets the applicable airworthiness standards. When a manufacturer earns a type certificate, the FAA is approving this specific design package.
Under FAR 21.31, the type design consists of:
- Drawings and specifications (and a list of them) that define the product's configuration and design features used to show compliance with the applicable certification rules.
- Information on dimensions, materials, and processes needed to define the structural strength of the product.
- The Airworthiness Limitations section of the Instructions for Continued Airworthiness, as required by Parts 23, 25, 26, 27, 29, 31, 33, and 35, or as otherwise required by the FAA (and as specified for special classes under § 21.17(b)).
- For primary category aircraft, an optional special inspection and preventive maintenance program a trained pilot-owner can perform.
- Any other data needed to compare later products of the same type for airworthiness, noise, fuel efficiency, fuel venting, and exhaust emissions.
Why it matters: this is the baseline configuration every production aircraft must conform to. Modifications outside the type design require approval (e.g., an STC).
Regulation Text
14 CFR § 21.31§ 21.31 Type design.
The type design consists of—
(a) The drawings and specifications, and a listing of those drawings and specifications, necessary to define the configuration and the design features of the product shown to comply with the requirements of that part of this subchapter applicable to the product;
(b) Information on dimensions, materials, and processes necessary to define the structural strength of the product;
(c) The Airworthiness Limitations section of the Instructions for Continued Airworthiness as required by parts 23, 25, 26, 27, 29, 31, 33 and 35 of this subchapter, or as otherwise required by the FAA; and as specified in the applicable airworthiness criteria for special classes of aircraft defined in § 21.17(b); and
(d) For primary category aircraft, if desired, a special inspection and preventive maintenance program designed to be accomplished by an appropriately rated and trained pilot-owner.
(e) Any other data necessary to allow, by comparison, the determination of the airworthiness, noise characteristics, fuel efficiency, fuel venting, and exhaust emissions (where applicable) of later products of the same type.
[Doc. No. 5085, 29 FR 14564, Oct. 24, 1964, as amended by Amdt. 21-27, 34 FR 18363, Nov. 18, 1969; Amdt. 21-51, 45 FR 60170, Sept. 11, 1980; Amdt. 21-60, 52 FR 8042, Mar. 13, 1987; Amdt. 21-68, 55 FR 32860, Aug. 10, 1990; Amdt. 21-70, 57 FR 41368, Sept. 9, 1992; Amdt. 21-90, 72 FR 63404, Nov. 8, 2007; Amdt. No. 21-107, 89 FR 12653, Feb. 16, 2024]
Oral Exam Questions a DPE Might Ask
Q1What is a type design and what does it include?
Per FAR 21.31, a type design is the package defining a certified product, including the drawings and specifications, dimensional/material/process data for structural strength, the Airworthiness Limitations section of the ICA, any optional pilot-owner inspection program for primary category aircraft, and any other data needed to evaluate later products of the same type.
Q2Where in the type design would you find the Airworthiness Limitations, and why are they important?
FAR 21.31(c) requires the Airworthiness Limitations section of the Instructions for Continued Airworthiness as part of the type design. These limitations contain mandatory replacement times and inspection intervals that must be followed to keep the aircraft airworthy.
Q3Does the type design address anything beyond airworthiness, like environmental factors?
Yes. FAR 21.31(e) requires data sufficient to determine, by comparison, the airworthiness, noise characteristics, fuel efficiency, fuel venting, and exhaust emissions of later products of the same type, where applicable.
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Related Sections in Part 21