Three mechanisms, and they run at once
Ultraviolet exposure degrades the topcoat continuously, which is why the finish goes flat on upper surfaces first: wing tops, the horizontal stabiliser, the spine. Moisture drives the second mechanism. FAA AC 43-4B, the FAA's 126-page guidance on corrosion control for aircraft, states that filiform corrosion under paint is inhibited by keeping relative humidity below about seventy percent and by washing off acidic airborne contaminants. Outside, the humidity is whatever the day brings, and in Georgia that is a great deal of it for much of the year. The third mechanism is thermal cycling: the airframe heats and cools through a wide range daily, and seals and sealants do that work with it. The same AC is clear about where responsibility sits — corrosion inspection frequency and treatment belong to the operator, under the manufacturer's recommendations or the operator's own program.
The cabin ages in parallel, and more visibly
Sunlight through the cabin windows does the damage you can see. Leather fades and hardens, veneer finishes dry, and carpet bleaches in a stripe down whichever side of the aisle faces the afternoon sun. None of it reverses with cleaning, and the cabin is the part of the aircraft your passengers actually sit in. The OEM manuals treat a cabin as a set of separate problems rather than one surface: Gulfstream's completion center maintenance handbook, chapter 12, carries distinct procedures for wood, granite, Lexan, vinyl laminate, plating, stainless steel, leather, vinyl, rubber, carpet and fabric. Eleven materials, eleven methods. It also warns that silicone-based household polishes leave an oily residue on the urethane wood finish that can prevent a later repair. Sun works on all eleven at the same time.
The failure mode is the repaint arriving early
This is the decision with the longest lever on paint life. Manufacturers generally recommend strip and repaint at five to six years, industry practice runs nearer seven, ten is treated as the outside limit, and around four years is normal where an aircraft lives in coastal salt air. An aircraft parked outside sits at the wrong end of that range. A full strip and repaint commonly takes five to seven weeks with the aircraft unavailable, and delaying it is worse than taking it, because tired paint hides corrosion that carries on working underneath. Two otherwise identical aircraft, one hangared and one not, do not reach their repaint intervals together, and the gap is visible long before either of them changes hands.
Correction spends a film that cannot be replaced
Paint correction works by removing a few microns of clearcoat to level the defect. An aerospace basecoat and clearcoat system builds to roughly two to two and a half mils of dry clearcoat, and that is the entire budget. It cannot be topped up without a repaint, and composite components need very specific film thicknesses because they flex. An aircraft outside accumulates the oxidation, water spotting and embedded contamination that correction is used to fix, so it spends that budget faster and reaches the end of it sooner. Protection is repeatable. Correction is not, and that is the case for treating an outdoor aircraft preventively rather than letting the finish go and recovering it later.
What it takes to hold the line, either way
A full interior and exterior on a midsize jet at a professional standard is a five-figure job before condition or deadline are factored in, and an aircraft that lives outside reaches that work sooner and needs more attention in between. On an outdoor aircraft we are the heavier program, deliberately. Fast work with household products is not a lighter version of the same job; it is a different job with a different outcome. Aviation chemistry is qualified against written specifications — AMS 1526 for exterior cleaners, Boeing D6-17487 for cleaners, waxes, polishes and compounds, whose battery includes seven-day sandwich corrosion, acrylic crazing, paint softening and a 150-hour hydrogen embrittlement immersion to ASTM F519 on notched cadmium-plated specimens at forty-five percent of load. A consumer product has not passed a test it was never submitted to. Aggressive interior method carries its own cost: it can take the fire retardant out of seat covering materials and carpet. The expensive outcome is never the program. It is the repaint you reached years early, and the weeks the aircraft spends in a paint shop rather than flying.
What changes the answer
Only availability. Where there is genuinely no hangar, the mitigations are unglamorous and they work: door and window seals kept serviceable, the cabin kept dry, shades down, a cover cut for the type rather than a generic one, and a shorter interval between washes because contamination is landing continuously rather than occasionally. One case gets worse outside rather than better, and that is a polished, unpainted airframe. Alclad is a thin pure-aluminium cladding over a corrosion-prone alloy, only about two to five percent of the sheet thickness, and polishing removes the oxide film that protects the surface, so a polished aircraft needs reworking at least three times a year by common practice. Outside, that clock runs faster still.