Part 43 Series — Major Repairs, Major Alterations & Form 337: When Maintenance Gets Serious

Changing oil? That’s preventive maintenance.

Replacing a landing light? Still preventive maintenance.

Installing a brand-new GPS navigator with structural panel changes and wiring modifications?

Now we’re in different territory.

Under FAR Part 43, not all maintenance is created equal. Some work is considered major repairs or major alterations, and once you cross that line, additional rules, approvals, and documentation requirements apply.

For private pilots flying small aircraft, especially owners, understanding the difference between minor and major work is critical. The distinction affects:

• Who can perform the work

• What data must be used

• Whether FAA Form 337 is required

• How the aircraft records must be updated

In this final article of our five-part Part 43 series, we’ll break down:

• Appendix A (major repairs & major alterations)

• Appendix B (recording requirements)

• When Form 337 is required

• Why this matters to your airworthiness

Let’s draw the line between minor and major.