Legal Interpretations
Rourke-2 2009
Summary
The Question
Can a non-TSO electronic flight display approved for IFR use in experimental or light-sport aircraft be installed for the same purpose in a primary category aircraft?
Background
Following up on an earlier 2009 interpretation about 14 CFR 91.205(d) and experimental and amateur-built aircraft, an individual who had already applied for an STC and petitioned for rulemaking asked about installing such a display in a primary category aircraft.
The FAA’s Interpretation
Not without a supplemental type certificate. The display is a major change in type design, so an STC is required (14 CFR 21.113, 14 CFR 21.115), and under 14 CFR 21.101 the applicant generally must show compliance with the category's airworthiness requirements in effect on the application date and with 14 CFR part 34 and 14 CFR part 36. Experimental-category approval does not carry over, and FAA approval is needed even for TSO-conforming equipment.
- Requester
- Rourke
- Issued
- April 22, 2009
- Subjects
- General Operating & Flight Rules · Aircraft & Parts Certification
Regulations Cited
Unreadable text from the scan (such as a barcode or stamp) is left out of the text below; the original letter shows it exactly.
Page 1
U.S. Department
of Transportation
Federal Aviation
Administration
APR 2 2 2'.109
Mr. William P. Rourke
Dear Mr. Rourke:
Office of the Chief Counsel 800 Independence Ave .. S.W.
Washington, D.C. 20591
This letter responds to your follow-up question to the interpretation issued to you on February 2, 2009 concerning Title 14 of the Code of Federal Regulations§ 91.205(d) ( 14 CFR § 91.205(d)). That interpretation addressed the applicability of§ 91.205(d) to experimental and amateur-built aircraft.
You now question "whether a non-TSO electronic flight display, which is approved for IFR flight in other Special Airworthiness Category aircraft (experimental, light sport) can be installed for the same purpose in a Special Airworthiness-Primary Category aircraft?" Since the electronic flight display you wish to install in a primary category aircraft introduces ~a .major ·.change in-that7.aircraft's type design, rou must apply for and-.receive a- -:: ::~.-:-:=· .... ; ... ._, supplemental type certificate ( STC) for that installation. Section 21.115 specifies that the altered product must meet the requirements of § 21.101. Under § 21.101, applicants for an STC must demonstrate that the changed product complies with the airworthiness requirements applicable to the category of the product in effect on the date of the application for this change and with parts 34 and 36 of this chapter.2 An electronic flight display is not approved for installation in a primary category aircraft simply because it was permitted to be installed in an experimental category aircraft. You will have to receive FAA approval for the installation of the fiight display regardless of whether the equipment conforms to a technical standard order.
This letter responds to your question in a general nature. In reviewing this matter, we see that you have already filed with the Atlanta Aircraft Certification Office (ACO) and FAA Small Airplane Directorate for an STC to allow the installation of an EFD in a primary category aircraft. {The Atlanta ACO requested additional information and to date, has not received any response from you.) In addition, you have a pending petition for rulemaking to 1 I 4 CFR § 21.113 provides. in part. that any person who alters a product by introducing a major change in type design, not great enough to require a new application for a type certificate under§ 21.19, shall apply to the Administrator for a supplemental type certificate.
2 l '4 CFR § 21.101 does provide exceptions to the requirements of paragraph (a). However, this interpretation responds to the general applicability of§ 21.101, as your letter did not specify the specific aircraft.
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permit such installation. The FAA's Certification Procedures Branch has advised us that they will be responding shortly to your petition for rulemaking on this issue. This response has been coordinated with the General Aviation Airworthiness Division, AFS-300, and the Certification Procedures Branch, AIR-110. If you have any questions, please contact Ms. Lorelei Peter at 202-267-3134.
Sincerely,
~~;:.~~~~~~------
Regulations Referenced
Snapshot retrieved August 6, 2026.