Get Field Approval Checklist

It is an approval by the Administrator, through an authorized Aviation Safety Inspector (airworthiness), of technical data and/or installations used to accomplish a major repair or major alteration.

There are three different kinds of field approvals for which the local FAA inspector can sign off: Examination of data only: This is the most common form of field approval.

For other records (i.e., FAA Form 337) related to STC's (major alterations), they become part of the permanent records of the aircraft, but are not required to be carried on board.

Form 337 Field Approval: (The installer should consult with their local airworthiness authority to determine if/when a Form 337 is required). If the TSO authorized battery is equal to the original certified design battery listed in the "Illustrated Parts Catalog" (IPC), the battery may be installed using FAA Form 337.

An STC is a more robust standard than a simple Form 337 that requires more engineering and proof that the intended modifications result in an airworthy plane.

The person who performs or supervises a major repair or major alteration must prepare FAA Form 337. The form is executed at least in duplicate and is used to record major repairs and major alterations made to an aircraft, airframe, powerplant, propeller, appliance, or a component part thereof.

The person who performs or supervises a major repair or major alteration must prepare FAA Form 337. The form is executed at least in duplicate and is used to record major repairs and major alterations made to an aircraft, airframe, powerplant, propeller, appliance, or a component part thereof.

Any STC is, by definition, a major alteration and also requires a 337 form. It seems to be a common practice for some mechanics to file a 337 form “just in case” in order to avoid any interpretation issues, but I would strongly advise against that approach. A 337 form is titled “Major Repair & Alteration” for a reason.