5.2 FAA Form 337: Preparation, Execution & Distribution

5.2 FAA Form 337: Preparation, Execution & Distribution

[!NOTE] Statutory Purpose of Form 337: FAA Form 337 (Major Repair and Alteration) serves two distinct regulatory mandates under Title 14 of the Code of Federal Regulations: it provides the aircraft owner/operator with a comprehensive written record of major repairs or alterations performed on their aircraft, and it provides the Federal Aviation Administration with the technical documentation necessary to verify conformity to approved data and maintain historical oversight of the civil aircraft fleet. The legal foundation for Form 337 is codified in 14 CFR § 43.9 and detailed in 14 CFR Part 43 Appendix B.

Regulatory Foundation: 14 CFR § 43.9 and Part 43 Appendix B

Under federal aviation law, standard maintenance logbook entries required by 14 CFR § 43.9 are legally insufficient for major repairs and major alterations. Whenever work meets the definition of a major repair or major alteration under 14 CFR Part 1.1 and Part 43 Appendix A, the executing technician and approving inspector must execute FAA Form 337 in accordance with the exacting procedures established in Part 43 Appendix B.

Form 337 is an enforceable federal legal instrument. Every statement entered upon it carries civil and regulatory accountability. Understanding how to properly prepare, execute, and distribute this form is central to the duties of an Inspection Authorization holder.

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Block-by-Block Execution of FAA Form 337

FAA Form 337 is organized into eight numbered items; the FAA uses "Item" and "Block" interchangeably in its own guidance. The authoritative instructions are AC 43.9-1G, Instructions for Completion of FAA Form 337 (11/1/19), which cancelled the older AC 43.9-1F that much study material still cites. Each item must be executed with precise regulatory fidelity:

Block 1: Aircraft Identification

Block 1 establishes the identity of the airframe upon which (or for which) the work is accomplished. It contains four required fields:

• Make: The manufacturer's corporate name as listed on the Type Certificate Data Sheet (e.g., Cessna, Piper, Beechcraft), not colloquial or marketing trade names.
• Model: The exact certified model designation from the aircraft data plate and TCDS (e.g., 172S, PA-28-181).
• Serial Number: The complete manufacturer's serial number exactly as stamped on the fireproof aircraft identification plate required by 14 CFR Part 45.
• Nationality and Registration Mark: The complete registration mark (e.g., N12345).

Block 2: Owner Information

Block 2 identifies the registered owner of the aircraft. It requires the owner's complete legal name and permanent mailing address exactly as recorded on the official FAA Aircraft Registration Certificate (AC Form 8050-3). If the aircraft has recently been sold, the current owner of record on file with the FAA Aircraft Registration Branch must be entered.

Block 3: For FAA Use Only (Field Approvals)

Block 3 is strictly reserved for the Federal Aviation Administration. Mechanics, repair stations, and IA holders must never write, sign, or stamp in Block 3.

• This block is used exclusively by an FAA Aviation Safety Inspector (ASI) to document an FAA Field Approval.
• When an alteration or repair relies on data requiring a field approval, the ASI reviews the data package, inspects the aircraft (if applicable), and endorses Block 3 with an official FAA stamp, signature, date, and FSDO identifier, certifying approval of the data or alteration under FAA Order 8900.1.

Block 4: Type (Classification of Work)

Block 4 categorizes the nature of the work performed. The technician must indicate:

• Whether the work is a Major Repair or a Major Alteration (checking the appropriate box).
• The specific aeronautical product affected: Airframe, Powerplant, Propeller, or Appliance.
• Multiple Selections: If an alteration affects both the airframe and the powerplant (such as installing an engine conversion kit that requires airframe structural reinforcement and a new engine mount), both boxes must be checked.

Block 5: Unit Identification

Block 5 provides granular traceability for the specific component repaired or altered.

• When an alteration is performed directly on the airframe, the fields in Block 5 correspond to the airframe data from Block 1.
• However, when a major repair or alteration is performed on an engine, propeller, or appliance (such as an overhauled hydraulic actuator, an engine cylinder repair, or an altered propeller hub), Block 5 must contain the specific Make, Model, Serial Number, and Type/Part Number of that individual unit. This ensures traceability if the component is subsequently removed and transferred to another aircraft.

Block 6: Conformity Statement (The Performer's Certification)

Block 6 is the legal statement of conformity executed by the person or facility that physically performed the maintenance, alteration, or repair.

• Text of Certification: The signer certifies that the repair and/or alteration made to the unit(s) identified in Block 5 and described in Block 8 was made in accordance with the requirements of 14 CFR Part 43 and that the information furnished is true and correct to the best of their knowledge.
• Signer Qualifications: Block 6 is executed by an appropriately rated certificated mechanic (A&P), a certificated repair station, or the product manufacturer.
• Signer Information: Includes the physical signature, date of completion, type of certificate held (e.g., Mechanic A&P), and certificate number.

Block 7: Approval for Return to Service (The Inspector's Certification)

Block 7 is the return-to-service certification executed by the person authorized under 14 CFR § 43.7 to approve the product for return to service.

• What the block actually says: Item 7 is headed "Approval for Return to Service" and reads that, pursuant to the authority given the persons specified below, the unit identified in Item 5 was inspected in the manner prescribed by the Administrator and is APPROVED or REJECTED — the signer checks one of those two boxes. The block does not contain the words "personally inspected," although § 65.95(a)(1) supplies that duty for an IA and AC 43.9-1G ¶ 8.7.3 states that before approving the form the signer must ensure the work described in Item 8 matches approved data and that the form is complete.
• Rejection route: a rejected form is returned to the person identified in Item 6 for correction; only approved forms go on to the Aircraft Registration Branch.
• Who checks the box: Item 7 provides check boxes identifying the finder — FAA Flight Standards inspector, manufacturer, inspection authorization, repair station, person approved by Transport Canada Civil Aviation, or "Other." An ASI signing Item 7 enters the office identifier in the "Certificate or Designation No." block.
• Signer Qualifications: For general aviation aircraft, Block 7 is executed by an Inspection Authorization (IA) holder, a certificated repair station, the original manufacturer, or an authorized FAA ASI.
• The IA Signature: The IA enters their signature, date of return-to-service approval, and certificate identification (Mechanic certificate number with "IA" designation).

Block 8: Description of Work Accomplished (The Narrative Heart)

Block 8 provides the complete, self-contained technical record of the work. If additional space is required, reverse-side continuation or attached supplementary sheets must be identified with the aircraft registration number, serial number, and date. Block 8 must contain five mandatory components:

1. Clear Statement of the Problem or Scope: A clear description of the damage repaired or the operational scope of the alteration.
2. Specific Citation of FAA-Approved Data: Explicit reference to the approved technical data used, including the issuing authority, document title, drawing number, revision level, and date (e.g., STC SA01234CH, installation drawing DWG-5001 Rev. D dated March 15, 2024). Generic references such as "repaired per FAA regulations" or "installed per STC" without drawing and revision numbers are legally invalid.
3. Chronological Narrative of Work: Detailed description of the methods, materials, structural dimensions, rivets, splices, and hardware installed.
4. Weight and Balance Recalculation: A clear statement documenting whether the aircraft's empty weight and center of gravity (CG) have changed, including the revised empty weight, arm, and useful load, or a statement stating: "Weight and balance change is negligible. Equipment list revised this date."
5. Instructions for Continued Airworthiness (ICA): If the alteration alters inspection intervals or maintenance procedures, Block 8 must state: "Instructions for Continued Airworthiness (ICA) have been provided to the aircraft owner/operator and incorporated into the aircraft maintenance records in accordance with 14 CFR § 23.1529 / § 25.1529."

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Summary of FAA Form 337 Execution Blocks

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Form 337 Distribution and Submission Rules

The statutory disposition of FAA Form 337 is governed strictly by 14 CFR Part 43 Appendix B:

Standard Two-Copy Distribution Rule — Appendix B(a)

For a major repair or major alteration not covered by one of the three exceptions, Appendix B(a) prescribes exactly three acts:

1. Execute FAA Form 337 at least in duplicate.
2. Give a signed copy of that form to the aircraft owner.
3. Forward a copy to the FAA Aircraft Registration Branch in Oklahoma City (P.O. Box 25504, Oklahoma City, OK 73125) within 48 hours after the aircraft, airframe, aircraft engine, propeller, or appliance is approved for return to service.

• Exam Trap — the destination: the FAA copy goes to the Aircraft Registration Branch, not to the local FSDO. The registry validates the form by matching the registration mark against the serial number and files it in the aircraft's permanent FAA record; a form mailed to a district office does not satisfy Appendix B(a)(3). Electronic Form 337 submissions route to the registry automatically.
• Exam Trap — the clock: the 48-hour clock begins at approval for return to service (Item 7), not when the last rivet is driven or when Item 6 is signed.
• Retention by the owner: the owner's copy of a Form 337 for a major alteration is a permanent record under § 91.417(a)(2)(vi) that transfers with the aircraft on sale; a Form 337 recording a major repair falls under § 91.417(a)(1) and need only be kept until the work is repeated or superseded, or for one year.

The Special Three-Copy Rule: Extended-Range Fuel Tanks — Appendix B(d)

Get the paragraph letter right: the extended-range fuel tank rule is Appendix B(d), not (c). Paragraph (c) governs a different case entirely — a major repair or major alteration made by a person authorized under § 43.17 (the Canadian maintenance-provider rule).

Appendix B(d) applies to extended-range fuel tanks installed within the passenger compartment or a baggage compartment. The person who performs the work and the person authorized by § 43.7 to approve it must execute FAA Form 337 in at least triplicate, and a completed copy must be:

1. Placed on board the aircraft as specified in § 91.417 — this is the on-board copy that lets an inspector verify the cabin fuel installation in the field;
2. Given to the aircraft owner; and
3. Forwarded to the FAA Aircraft Registration Branch, Oklahoma City, within 48 hours after the work is inspected.

Two fine points the exam exploits: the trigger is the tank's location (passenger or baggage compartment), so wing or wingtip auxiliary tanks stay on the ordinary two-copy rule; and paragraph (d) starts its 48-hour clock after the work is inspected, whereas paragraph (a) starts it after approval for return to service. AC 43.9-1G ¶ 8.6.5 adds the mechanical detail that the fuel-tank modification box is checked in Item 6 of the form.

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Form 337 Distribution and Recording Matrix

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Certificated Repair Station Alternative Recording

Under 14 CFR Part 43 Appendix B, paragraph (b), a certificated repair station possesses an alternative method for recording major repairs made in accordance with a manual or specifications acceptable to the Administrator:

• A certificated repair station is not required to complete FAA Form 337 for a major repair, provided the repair station:
  1. Issues a Maintenance Release containing the customer work order number, date, signature, and certificate number of the repair station.
  2. Gives the aircraft owner/operator a signed copy of the maintenance release and a copy of the completed work order describing the work done.
  3. Retains a duplicate copy of the work order for at least 2 years from the date of approval for return to service.
• The Critical Regulatory Trap: This alternative applies exclusively to major repairs. It never applies to major alterations! A certificated repair station that performs a major alteration must execute FAA Form 337 and submit a copy to the FAA within 48 hours.

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High-Yield Exam Traps & Regulatory Distinctions

• The 48-Hour Trigger: The 48-hour submission deadline to the FAA runs from the date of return-to-service approval (Block 7), not the date the maintenance was physically performed (Block 6).
• Separation of Signatures: The mechanic who performs the repair signs Block 6 as an A&P. The IA who inspects and approves the work signs Block 7 with their IA designation. Even if one person performs both tasks, they must sign in both distinct capacities.
• Extended Fuel Tanks: Auxiliary tanks installed in wings stay on the ordinary Appendix B(a) two-copy rule; only tanks installed within the passenger compartment or a baggage compartment trigger the Appendix B(d) three-copy rule and the on-board copy.
• Repair Station Exemption Scope: Repair stations can substitute a maintenance release and work order only for major repairs; major alterations always mandate Form 337.