How often should an aircraft be washed

There is no published interval from the FAA and none from the business jet manufacturers that is publicly available. What does exist is military data, an international standard for how corrosive different environments are, and the honest observation that where an aircraft lives matters more than how many hours it flies.

This is the most asked question in this category and almost every answer to it online is invented. So here is what is actually documented, and then what we do about it.

What the FAA says, and what it does not

FAA Advisory Circular 43-4B, Corrosion Control for Aircraft, lists thirteen elements of a corrosion prevention and control program. Four of them are relevant here:

• Aircraft washing at regularly scheduled intervals
• Routine cleaning or wipe down of all exposed unpainted surfaces
• Keeping drain holes and passages open and functional
• Periodic thorough cleaning, lubrication and preservation

Notice what item five says and does not say. Regularly scheduled intervals. No number. The AC nowhere states a washing frequency.

What it does say is that aircraft exposed to such environments as salt air, heavy atmospheric industrial pollution, or over-water operations will need a more stringent program than an aircraft operating in a dry environment. That is the actual guidance: the environment sets the interval.

So if you have read that the FAA recommends washing every thirty days, or sixty, or ninety, that is folklore. It is not in the document.

What the airframe manufacturers publish

Less than you would hope. Gulfstream, Bombardier and Embraer maintenance manuals are proprietary, and no publicly accessible interval for exterior washing exists for any of the three that we have been able to verify. If someone quotes you one, ask which chapter it came from.

What is public is instructive anyway. Cessna’s own pilot operating handbook language for the 172S says the painted surfaces can be kept bright by washing with water and mild soap, that harsh or abrasive soaps or detergents should never be used, and then this: if the airplane is operated in a seacoast or other salt water environment, it must be washed and waxed more frequently to assure adequate protection. It also says special care should be taken to seal around rivet heads and skin laps, which are the areas most susceptible to corrosion.

Again: no number. Environment sets it, and the seams are the point.

The military does publish numbers

The only organizations that state intervals in public are the ones that operate fleets in known environments and have to write it down.

NAVAIR 01-1A-509-2, the Navy and Army cleaning and corrosion control manual, states that Navy aircraft shall be cleaned at least every 7 days when aboard ship and at least every 14 days when ashore. It adds that when deployed within three miles of salt water, or when flown below 3,000 feet over salt water, daily cleaning or wipe down is required on all exposed unpainted surfaces.

The Air Force works on a different model. A published corrosion research paper describes Air Force wash intervals as determined by base corrosion severity, ranging from 30 to 180 days depending on whether a base environment is rated mild, moderate or severe.

Neither of these is a business jet. Navy aircraft live in a far harsher environment than almost any corporate aircraft. But the shape of the answer is the useful part: a six-fold difference in interval, driven entirely by environment.

How to know which environment you are actually in

ISO 9223 classifies atmospheric corrosivity from C1 to CX. The typical environments it names:

• C2, low. Rural areas with low pollution.
• C3, medium. Urban areas, and coastal areas with low chloride deposition.
• C4, high. Coastal areas without salt water spray. Also areas with de-icing salt exposure.
• C5, very high. Coastal areas, sheltered positions on a coastline.
• CX, extreme. Subtropical and tropical zones with a strong chloride effect, coastal and offshore areas.

Between C2 and C5 the published first-year corrosion rate for carbon steel differs by roughly an order of magnitude. Two cautions on that: those published rates are for carbon steel and zinc, not for clad aluminum airframe alloys, and the category depends on actual chloride deposition rather than on distance from water alone. But the direction is not in dispute.

The same corrosion research paper mentioned above rated Daytona Beach as a very severe environment, central Ohio as moderate and Robins Air Force Base as mild, and recorded an operational contrast: an aircraft at a moderate base on a 120 day wash interval, against one in a severe coastal environment on 30 days.

What we actually do

We work coastal salt, desert UV, industrial fallout and de-ice country at the same time, which is the only reason we can answer this with anything other than a shrug. The pattern that holds up:

Coastal salt exposure, aircraft outdoors. Our tightest intervals. Salt is water soluble and it needs water to leave, and it collects in exactly the seams the Cessna language warns about. This is Naples, West Palm Beach, Boca Raton, Fort Lauderdale, Opa-locka, Miami and Stuart. The aircraft that get into trouble here are the ones on a schedule written for somewhere else.

Coastal, hangared. Longer, but not as much longer as people assume. A hangar removes UV and rain. It does not remove humidity or the chloride already on the airframe. More on that here.

Dry inland. The longest intervals we run, at Scottsdale and Las Vegas. The driver there is UV and dust rather than corrosion, and the risk shifts from the structure to the finish.

De-ice country. Interval is driven by the season rather than the calendar. Glycol residue wants removing before it sits through a summer, which is its own subject.

Underneath all of it, the rhythm most operators land on is a full wet wash at an interval set by where the aircraft lives, with lighter maintenance in between so it looks right without anybody abrading it.

The honest summary

Anyone who gives you a single number for this without asking where the aircraft is based is not answering the question. If you tell us where it lives, how it is stored and how it is used, we will tell you what we would put it on and why. That is what the scheduled programs are, and the reason they are worth having is not the discount. It is that the interval stops depending on somebody remembering.