Legal Interpretations
Rude 2015
Summary
The Question
Is an alteration listed in the aircraft, aircraft engine, or propeller specifications, done as described there, a major alteration requiring an FAA Form 337?
Background
A requester asked how the 14 CFR 1.1 definition of "major alteration" treats alterations listed in the aircraft, aircraft engine, or propeller specifications, what criteria would make one major, and whether FAA Form 337 must be filed.
The FAA’s Interpretation
No. Under 14 CFR 1.1, a major alteration is an alteration not listed in the aircraft, aircraft engine, or propeller specifications, so a listed alteration is not a major alteration. Because 14 CFR 43.9(d) and appendix B to 14 CFR part 43 require FAA Form 337 for major repairs and major alterations, a listed alteration does not require one.
- Requester
- Rude
- Issued
- December 8, 2015
- Subjects
- Maintenance & Repair Stations · Definitions
Regulations Cited
Page 1
U.S. Department
of Transportoflon
Fe deral Aviation
Administration
DEC - 8 2015·
Mr. David Rude
Re: Interpretation of "Major alteration" in 14 CFR § l. l
Dear Mr. Rude:
Office of the Chief Counsel
800 Independence Ave .. SW.
Washington. DC 20591
This letter responds to yom August 5, 2015 request for a legal interpretation of the definition of the term "major alteration." You posed a number of questions, each of which is addressed below.
In your request you specifically ask whether an alteration listed in the aircraft, aircraft engine, or propeller specifications, when implemented as described in those specifications, is merely an alteration and therefore not a major alteration.
The term "major alteration" is defined in 14 CFR § 1.1 . As stated in that section:
Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications- ( I) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or (2) That is not done according to accepted practices or cannot be done by elementary operations.
In accordance with this definition, an alteration listed in the aircraft, aiJcraft engine, or propeller specifications is not a major alteration.
If an alteration listed in the aircraft, aircraft engine, or propeller specifications is determined to be a major alteration, you then ask what criteria are used to make that detetmination. Again, since the alteration is listed in those specifications it is not a major alteration. Lastly, you ask whether an alteration listed in the aircraft, aircraft engine, or propeller specifications, when implemented as described in those specifications, requires an FAA Form 337, Major Repair and Alteration, to be filed.
Paragraph (d) of 14 CFR § 43.9 states:
Page 2
Paragraph (d) of 14 CFR § 43.9 states:
(d) In addition to the entry required by paragraph (a) of this section, major repairs and major alterations shall be entered on a form, and the form disposed of, in the manner prescribed in appendix B, by the person performing the work. Paragraph (a) of Appendix B to Part 43 states:
(a) Except as provided in paragraphs (b), (c), and (d) of this appendix, each person performing a major repair or major alteration shall-
(1) Execute FAA Form 337 at least in duplicate;
(2) Give a signed copy of that form to the aircraft owner; and (3) Forward a copy of that form to the FAA Aircraft Registration Branch in Oklahoma City, Oklahoma, within 48 hours after the aircraft, airframe, aircraft engine, propeller, or appliance is approved for return to service.
Since the alteration you refer to is listed in the aircraft, aircraft engine, or propeller specifications it is not considered a major alteration and an FAA Form 337 is not required to be filed.
This response was prepared by Paul Greer, an attorney in the Regulations Division of the Office of the Chief Counsel and coordinated with the Aircraft Maintenance Division (AFS-300) of the Flight Standards Service. If you need fmther assistance you may contact us at (202) 267-3073.
Sincerely,
Lorelei Peter
Acting Assistant Chief Counsel
for Regulations, AGC-200
Regulations Referenced
Snapshot retrieved August 6, 2026.