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Belly and gear included, or exterior only?

Name: JetRefined
Address: Atlanta, GA, US
Telephone: (770) 999-9740
Price range: $$$

Include the belly and gear. The top of the aircraft is the part that gets photographed. The underside is the part holding hydraulic fluid, fuel residue, exhaust soot and brake dust against the skin and into the joints, where moisture and acidic contamination stay in contact with structure. Exterior-only is a different job with a real purpose: a cosmetic turn before an event. As a standing program, it cleans everything except the part that decides how the airframe ages.

The short answer

Include the belly and gear. It is the least glamorous part of the aircraft and the part with the most at stake: accumulated belly soil holds corrosive material against structure, and an exterior-only wash never reaches it.

compared with
	Belly and gear included	Exterior only
What it is	A degrease, quoted as its own scope of work: qualified chemical, protection of anything that must not take it, gear bays and wheel wells worked by hand, and a plan for the effluent.	A cosmetic turn on the surfaces you can see from the ramp. A different product with a different purpose, not a reduced version of a degrease.
Method	Cleaners qualified for aircraft surfaces, applied deliberately around bonding points, static discharger bases and anything plated, then rinsed and the water controlled.	Cleaner applied to painted upper and side surfaces, then rinsed or encapsulated. Standard airframe cleaning doctrine states a dry wash is not suitable for heavy carbon, grease or oil, so it cannot do this work at all.
What it addresses	The soils that hold moisture and acidic contamination against skin, seams, lap joints and fastener heads.	Airport film, dust and light soil.
How long it holds	Belly soil rebuilds with flying hours, so the interval follows utilisation and exhaust deposition rather than appearance.	Looks right until the next few sectors. Nothing underneath has changed.
Downtime	More crew hours, and the aircraft has to be positioned where the underside can be worked and the water controlled.	Shorter, and it fits into tighter windows between movements.
Risk	Chemical in the wrong place. Product selection is the whole control, which is why qualification against a published standard matters more than the label on the drum.	The one you cannot see. Soil left in place conceals corrosion, and a weeping fitting stays hidden in it.
Diagnostic value	High. A seeping strut or a weeping hydraulic fitting is obvious the day it starts on clean metal.	None below the cabin floor. Nothing under there is being looked at by anyone.
Pre-buy and inspection	Belly, wheel wells and gear legs can be assessed on arrival, because condition is visible.	A spotless top over a neglected belly slows the inspection: the area has to be cleaned before anyone can look at it.

What is actually under there

The belly collects a specific cocktail: hydraulic fluid, fuel residue, engine oil, grease thrown off the gear, brake dust, exhaust soot and whatever the runway lifts. Those soils hold moisture and acidic contamination against the skin and work it into seams, lap joints and fastener heads. Accumulated belly soils are documented as trapping corrosive material and worsening corrosion attack on structure. FAA AC 43-4B, the governing corrosion-control guidance, names washing as a control on filiform corrosion under paint, because washing removes the acidic airborne contaminants that drive it. That is the mechanism by which a cosmetic problem becomes a structural one.

A wash and a degrease are different jobs

Standard airframe cleaning doctrine separates them, and the separation is not commercial. A dry wash removes airport film, dust and light soil where water is undesirable or impractical, and is expressly not suitable for heavy carbon, grease or oil, particularly in engine exhaust areas. A wet wash removes oil, grease, carbon deposits and most soils, though not corrosion or oxide films. Belly and gear work is a third thing again: qualified degreasers rather than a general exterior cleaner, protection of everything that must not take chemical, hand work around bonding points and static discharger bases, and a plan for the effluent, because this is the dirtiest water on the aircraft.

What qualifies a chemical for a gear bay

This is the part that is checkable, and it is why the product matters more than the technique. AMS 1526 qualifies cleaners for aircraft exterior surfaces: no corrosion to aluminium, magnesium and steel alloys, and no adverse effect on acrylic glazing or on painted and unpainted surfaces. Boeing D6-17487 goes further. Its battery includes sandwich corrosion over seven cyclic days with product-saturated filter paper between faying aluminium surfaces, immersion corrosion, acrylic crazing, paint softening, and hydrogen embrittlement to ASTM F519: four notched cadmium-plated specimens held at 45 per cent of load and immersed for 150 hours. Plated high-strength steel is exactly what lives in a gear bay. A degreaser off an industrial shelf has not passed that test, because it was never submitted to it.

The failure mode of choosing exterior-only

It fails quietly. The aircraft looks maintained for years while the part that decides structure goes untouched, so there is no visible signal that anything is wrong. The signal arrives at a scheduled inspection or a pre-buy, and it arrives as a finding: corrosion under grime, or a fitting that had been weeping for months into soil thick enough to hide it. Nobody chooses that outcome. They choose a wash that looked complete, because everything they could see was clean, and the underside was never on the scope.

Clean metal shows leaks

There is a diagnostic benefit here that has nothing to do with appearance. A clean belly and clean gear bays make leaks visible. A weeping hydraulic fitting or a seeping strut shows immediately on clean metal and disappears entirely into old grime. Flight departments that degrease on a schedule find those things early, while they are small and while the aircraft is somewhere convenient. Departments that do not find them at a scheduled inspection, later and larger, on a date somebody else picked.

What changes the answer

Utilisation and exhaust deposition move the interval more than anything else. A turbine laying soot aft of the nacelles builds soil faster than a lightly flown piston, and gear bays on an aircraft flying hard collect grease faster than one that sits. Storage matters too: filiform corrosion under paint is inhibited by keeping the aircraft below 70 per cent relative humidity, and an open ramp in Georgia offers no humidity control at all. Anything heading for a pre-buy, an appraisal or a listing moves to the front of the queue regardless of where it sits in the cycle.

Why the fuller scope is the standard

Not because it is a better deal. Because of where the responsibility sits. Under FAA AC 43-4B, corrosion inspection and treatment remain the operator's responsibility, set against the manufacturer's recommendations or the operator's own program, and washing is one of the named controls. The soils that drive the problem collect on the underside. A program that leaves the underside out is a cosmetic program, whatever it is called. A scheduled degrease is crew hours on a date you choose, with the aircraft serviceable afterwards. Corrosion found under years of accumulated soil is shop work on a schedule that is not yours, measured in days or weeks. The real choice is when the work happens, not whether.

Choose when

Choose it for any aircraft on an inspection cycle, any turbine laying soot aft of the nacelles, anything parked outside, and anything about to be inspected, appraised or sold. Choose it if you would rather find a weeping fitting on a date you picked than at an inspection. On a recurring interval it is the part of the airframe most often left off a scope, and the part where leaving it off shows up in the structure rather than in the paint.

Choose when

Choose it when a specific event decides the job: a photography call, a board flight, an owner arriving in two hours. Choose it when the underside came out of a full degrease recently and is mid-interval, so the belly needs nothing yet. It is a legitimate piece of work with a defined purpose, and we do it properly. It is a different product from a degrease, not a lighter version of one, and it is not a maintenance program.

Questions we get on this

How often should the belly and gear be degreased?: Tie it to utilisation and exhaust deposition rather than the calendar. FAA guidance leaves corrosion inspection and treatment to the operator, the manufacturer's recommendations or your own program, so the interval is yours to set. We will propose one against your flying and then hold it.
Is degreasing safe around seals, bushings and plating?: Yes, with products qualified for aircraft surfaces, and the product is the whole control. AMS 1526 qualifies exterior cleaners as causing no corrosion to aluminium, magnesium and steel alloys. Boeing D6-17487 adds sandwich corrosion, immersion corrosion, acrylic crazing, paint softening and a 150-hour ASTM F519 hydrogen embrittlement test on notched cadmium-plated specimens. Anything that must not take chemical is protected before a drop is sprayed.
Can a dry wash clean the belly?: No. A dry wash exists to remove airport film, dust and light soil where water is undesirable or impractical, and standard airframe cleaning doctrine states plainly that it is not suitable for heavy carbon, grease or oil, particularly in engine exhaust areas. Belly work needs qualified degreasers and rinse.
Will exhaust staining come off completely?: Usually a substantial improvement. Staining that has stood for years and etched into the finish may not come back entirely, and we will tell you that before we start rather than discover it with you on the day. Tracking aft of the nacelles responds best when it is addressed regularly.
Does a clean belly really matter at a pre-buy?: Yes. An inspection does not stop where a cosmetic clean stops. Belly, wheel wells, gear legs and door jambs all get looked at, and clean metal lets condition be assessed and leaks be seen. Grime reads as neglect, fairly or not, and it slows the inspection, because the area has to be cleaned before anyone can look.

Send the tail number, the airport and when the aircraft is next on the ground for long enough to be worked. We will quote belly and gear against a written scope, tell you what condition we expect to find underneath, and set an interval that fits your inspection cycle rather than ours.

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Other decisions

vs Dry wash between trips, wet wash when the soil load is heavier than film. Neither one substitutes for the other, and that line is drawn by what each method removes, not by preference. vs Rinse-less, unless the ramp allows no water or the airframe carries nothing more than a dusting. It takes a wider band of soil and it is the gentler of the two when it is done to method. Dry wash is the right answer inside its limits and a poor one outside them. vs Coat paint you intend to keep. On paint already booked for the shop, wash it correctly instead and coat the new finish while it is perfect. vs Correct the paint only when the gauge shows the film can afford it; if a repaint is within a year or two, or the paint has already been polished more than once, live with the defects and protect what is left. vs Correct while the film is sound. Once the clearcoat itself is failing, polish is a delaying tactic and the repaint is the job you are actually buying. vs Maintenance is how you reach the repaint interval in good condition, not how you avoid it. If the paint is due, paint it.

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