When FAA Form 337 is used

Part 43 addresses maintenance, preventive maintenance, rebuilding, and alteration. Appendix A to Part 43 identifies major alterations, major repairs, and preventive maintenance categories.

The person classifying the work should evaluate:

• Product affected: airframe, powerplant, propeller, or appliance.
• Scope and complexity.
• Effect on weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other airworthiness qualities.
• Whether the work can be done by elementary operations.
• Approved or acceptable data required.
• Any special reporting or field-approval process.

Do not decide that a repair is minor merely because the physical area is small.

Form 337 block-by-block review

Use the actual current form and AC instructions. This summary is an audit aid, not completion authority.

Approved data and field approvals

A major repair or alteration generally requires appropriate approved data. Depending on the work, the support may include:

• Type Certificate or Supplemental Type Certificate data.
• Airworthiness Directive.
• FAA-approved manufacturer data.
• Designated Engineering Representative-approved data.
• Field-approved data.
• Other data approved under applicable authority.

The FAA describes the field approval process for a specific serial-numbered aircraft. A field approval is not interchangeable with an STC and is not suitable for every project.

Description of work

Block 8 and attachments should let a qualified reviewer understand:

• What was removed, repaired, or installed.
• Exact location.
• Product and component identity.
• Approved data and revision.
• Materials and major processes.
• Drawings, diagrams, or instructions.
• Tests and inspections.
• Operational limitations.
• Weight-and-balance change.
• Flight-manual or placard change.
• Instructions for continued airworthiness.
• Attachments that form part of the record.

Avoid vague language such as “installed per manufacturer data” without identifying the data.

Form 337 and the maintenance entry

The form does not eliminate other maintenance-record requirements. Reconcile it with 14 CFR 43.9, the associated maintenance entry, and the detailed work package.

The record set should connect:

• Work performed.
• Date.
• Person performing or supervising.
• Approval for return to service.
• Aircraft or component time where relevant.
• Approved data.
• Parts and release evidence.
• Inspection and test results.
• Configuration changes.

Filing and record disposition

Part 43 Appendix B and AC 43.9-1G address disposition. Use current FAA instructions for timing, copies, electronic submission, and special cases.

From a records-control perspective, preserve:

• Final signed form.
• FAA-accepted or filed copy evidence.
• All referenced attachments.
• Approved data.
• Maintenance entry.
• Work order and task cards.
• Weight-and-balance and equipment changes.
• Continued-airworthiness instructions.
• Photos and inspection evidence when material.

An expired OMB date printed on an older PDF does not itself answer whether the form or process is current. Use the FAA’s active form and guidance pages.

Reviewing an existing Form 337

Check:

1. Aircraft and owner identity.
2. Repair or alteration classification.
3. Unit identification.
4. Performing agency and certificate.
5. Return-to-service authority.
6. Dates and signatures.
7. Approved-data reference.
8. Work description and attachments.
9. Weight and balance.
10. Flight-manual supplements and placards.
11. Instructions for continued airworthiness.
12. Physical aircraft configuration.
13. Related maintenance entries.
14. FAA aircraft-file copy where available.

Record discrepancies; do not “fix” the historical form by editing the source file.

Common Form 337 records problems

• Wrong aircraft or component serial number.
• Owner name inconsistent with the period.
• Missing signature, certificate, or date.
• Approved data not clearly identified.
• Attachment referenced but absent.
• Work description too vague to reproduce or inspect.
• Weight-and-balance change missing.
• STC or flight-manual supplement absent.
• Continued-airworthiness tasks not added to tracking.
• Physical configuration differs from the record.
• Form appears in FAA file but not aircraft records, or vice versa.

Each problem has a different corrective path. Use qualified maintenance, engineering, legal, and FAA support as appropriate.

Form 337 in a pre-buy or financing review

For each material form:

• Identify the affected system and value consequence.
• Confirm the work is physically present.
• Review the approved data and completeness.
• Find subsequent inspections or repeat issues.
• Confirm continued-airworthiness requirements.
• Check damage and repair disclosure.
• Connect the form to valuation and lender diligence.

The absence of a Form 337 in a search is not proof that no major repair or alteration occurred. Review the full records and physical aircraft.

Sources and further reading

• FAA AC 43.9-1G, Form 337 instructions
• FAA field approval process
• 14 CFR Part 43 Appendix A
• 14 CFR Part 43 Appendix B
• FAA AC 43-9D