Updated . Educational only — not tax, legal, or lending advice. Confirm figures with your CPA, the state revenue department, and a lender before you close.
Avionics, Engine, and Interior STCs Are Three Different Loans
An STC is a specific approved modification, not a synonym for “upgrade.” Whether a lender will add it to the note depends on the category. The process for getting a mod funded is on the step-by-step STC financing page. The value and insurance discussion is on avionics and cabin STC economics.
Avionics
A glass-panel STC with a known installer, a written invoice, and a supplemental type certificate number is the easiest modification to describe in a security agreement. Lenders still do not assume the full invoice becomes aircraft value. They look at what comparable sales with that panel actually bring. Ask the appraiser to value the airplane as it will be delivered, not as it sits today, and put that number next to the loan.
Engine and propeller
A factory-reman or a field overhaul changes time-to-TBO, which is the number lenders already use on piston collateral. Financing the overhaul at purchase is common. Financing it two years later, on an aircraft that is otherwise paid down, is a new advance against a used airframe. Bring the work order, the warranty, and the logbook entry. A verbal “we’re going to overhaul” does not increase the appraisal.
Paint and interior
Cosmetic work is the category most often declined as a standalone loan. It helps a sale. It rarely supports new principal by itself. If it is bundled into a purchase, it belongs inside the purchase price and the appraisal, not in a second note secured by seat leather.
Unapproved modifications, or field approvals you cannot document, do the opposite of an STC: they give the lender a reason to cut the advance. If it is not in the logbooks with the 337 or the STC reference, it is not collateral.
Questions buyers actually ask
Can I finance an STC on an aircraft I already own free and clear?
Sometimes, as a cash-out or a modification loan, if the after-mod appraisal covers the new principal at the lender’s maximum loan-to-value. Many purchase lenders do not offer this product. Ask before you schedule the shop.
Does the shop get paid by the lender?
At closing, escrow pays the seller and, if the mod is part of the deal, the shop against invoices. Do not expect the lender to pay a shop directly six months later unless that draw structure is in the note.