Aircraft buyer guide
FAA Form 337: reading major repair and alteration records
FAA Form 337 records major repairs and major alterations. Read the work description and supporting references before interpreting it: a modification record is not automatically an accident record, and the absence of a form is not proof that no damage occurred.
By Aerovidence · Reviewed
Start with the purpose of the form
FAA AC 43.9-1G explains Form 337 and its use for recording major repairs and alterations, their details and approvals. The form can concern an airframe, powerplant, propeller or appliance. Identify the subject and the work described before adding it to an aircraft history timeline.
Official references: FAA AC 43.9-1G: instructions for Form 337. Sources checked .
Read the document in a consistent order
This reading sequence helps you prepare questions; it is not an approval of the work or the form. Preserve the exact wording of ambiguous entries for the qualified reviewer.
| Document detail | Buyer review question |
|---|---|
| Aircraft and unit identity | Do the manufacturer, model, serial and marked unit match the item being researched? |
| Type and description of work | What repair or alteration is actually described, and when? |
| Referenced data | Are the named drawings, approvals, STC or other attachments available? |
| Approval entries | Which entries and supporting records should the mechanic verify? |
| Later documents | Was the configuration subsequently changed, removed or superseded? |
Find the copies and supporting records
Ask the seller for the relevant forms and attachments with the maintenance records. The FAA aircraft-records service is another place to request recorded copies. An index entry or short summary is a pointer to a document, not a substitute for reading its contents.
- List the form references found in the supplied logs.
- Match each reference to an actual document and its attachments.
- Compare identity and work dates across the copies.
- Record any missing pages or contradictory descriptions for follow-up.
Official references: FAA Request for Copies of Aircraft Records · FAA AC 43.9-1G: instructions for Form 337. Sources checked .
Separate repair evidence from accident evidence
An alteration may document an equipment or design change. Even when a form describes a repair, read the actual evidence before assuming a cause or calling it accident damage. Search relevant NTSB records separately and confirm the physical airframe and event date. A same-mark result can belong to another aircraft.
Official references: NTSB aviation data and statistics. Sources checked .
Bring unresolved configuration questions to inspection
Ask the mechanic to compare the documents with what is physically installed, including any later changes. Keep “document not supplied,” “identity unresolved” and “reviewer identified a discrepancy” as separate observations. Aerovidence does not verify repair quality, authenticate approvals or provide a complete Form 337 inventory for an aircraft.
Check the public records first
How Aerovidence handles evidence · Sources and coverage limits
Continue your research
FAA aircraft records: what to request before a purchase
Find the official FAA aircraft records request, distinguish registration and airworthiness documents from maintenance logs, and organize a buyer review.
Aircraft STC lookup: research a modification before a prebuy
Find FAA supplemental type certificate information, separate design approval from installed equipment, and prepare the supporting records for a prebuy.
Aircraft logbook review: questions for a prebuy
Prepare an aircraft logbook review with an independent mechanic: check identities, dates, continuity, repairs, component changes and missing evidence.
How to check aircraft accident and incident history
Research NTSB aircraft accident records by registration and identity, distinguish report stages, and keep missing records separate from a clean history.