Why All Aircraft MUST First Be Painted GREEN?
Brand new airplanes are painted green … to save your life … not just from an aviation accident,
but also from cancer! Yes, there is safety in colors. If you’re wondering why that middle
aircraft is painted in silver, and not green, wonder no more. That one is not painted at all.
It’s … nude. Yes, there is safety in nudity … for some airplanes. Very few airplanes are painted
in black, and no, it has nothing to do with sunlight absorption and air conditioning costs.
But why aircraft under assembly used to be painted yellow, then at times pink,
then green, and why the days of nude aircraft are over, is Not What You Think!
The biggest enemy of an aircraft over its lifetime is corrosion from the elements,
well, that’s if you exclude rockets and missiles! The elements can weaken parts of
the aircraft and lead to a premature failure due to metal fatigue, which can result in a crash.
A recent example of this was in 2016, when the landing gear of a FedEx cargo jet collapsed,
as it had been weakened by corrosion. This resulted in the aircraft skidding off the runway,
causing a fire. Many corrosion-caused incidents happen every year, primarily on smaller planes,
and usually due to insufficient maintenance. But maybe the most famous accident was the
Aloha Airlines Flight 243, where part of the fuselage blew off mid flight.
The National Transportation Safety Board later concluded that the accident was
due to metal fatigue exacerbated by crevice corrosion. And since that aircraft operated
in a coastal environment, exposure to salt and humidity had made the corrosion much worse.
But there’s no need to worry! A big part of aircraft maintenance and inspection
is to look for signs of corrosion. This is why several times throughout the life of an aircraft,
all paint is stripped off, the entire aircraft is inspected for signs of corrosion,
problematic parts are fixed, and the aircraft is then repainted.
If by now you’re thinking that aircraft are painted green to prevent corrosion, that’s a
good guess, it’s just that the anti-corrosive agent used, is not green, It’s YELLOW.
The fight against corrosion began with automobiles, when in the 1920s, Ford Motor Company
started using zinc chromate as an anti-corrosion agent that was applied to aluminum surfaces to
prevent the build-up of rust. In the 1940s, zinc chromate was adopted by the US Military,
and the aviation industry as a whole. All aluminum aircraft parts were coated
with zinc chromate to protect their surfaces against corrosion by oils, grease and moisture.
The anti-corrosion coating resulted in yellow airplanes. Of course paint was later added on top.
But soon the toxic nature of the zinc chromate coating became evident, when a large number of
factory workers started developing lung cancer. Another side effect was tissue ulceration. To
combat this problem, other chemicals were mixed with zinc chromate to inhibit its carcinogenicity
… and they were successful. Replacing chromates with trivalent chromium or phosphates considerably
reduced the toxicity of the coating. But it also decreased the durability of the coating.
The solution was to add additional chemicals to increase the durability,
one of which was lamp black. Lamp black is a type of carbon black; the same material that makes
your car’s tires and submarines, black. It just happened that adding lamp black to zinc chromate
resulted in a green color. The more lamp black was added, the greener the coating looked. The
addition of lamp black to the mix results in a more UV-resistant coating, without which
the anti-corrosion properties quickly degrade. Lamp black was like sunscreen for airplanes!
This is especially valuable, considering that airplane parts are often transported
on trains under direct sunlight, and how production planes sit around under the sun.
But some interior parts of airplanes which are not exposed to the elements at all,
are also painted green … but for a completely different reason. The original yellow zinc
chromate paint was used for all aluminum parts of the airplane, including the interior.
The bright yellow would result in excessive glare and eyestrain for the pilots,
and thus US Air Force issued banned the use of plain yellow zinc chromate in interior areas of
the aircraft. Instead they asked manufactures to use green colors of their liking. Interestingly,
Soviets came to the same conclusion, which is why their cockpits were also painted green.
In fact surgeons wear green or blue in the operating room, as these colors reduce eye
strain. Also since green and blue are the opposite of red on the spectrum of visual light,
and during an operation, a surgeon is focusing on the … red stuff,
when they look up at their colleagues, they won’t see an illusive afterimage.
Speaking of red stuff, sometimes instead of lamp black, Indian Red pigments were mixed
with zinc chromate primer, resulting in a pinkish color. This was extensively used on F4U Corsairs.
Yes, the most capable carrier-based bombers of World War II … wore pink underneath!
Coming up next, 50 shades of green, and nude airplanes! Don’t block the view!
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Different manufacturers use different shades of green as there is no one universal formula
for the coating. Boeing uses a dark green, while Gulfstream’s coating is a somewhat lighter green.
Airbus does olive, but Russian manufacturers paint them in yellow. We’re actually not sure why!
But what is even more interesting is that sometimes you can see different shades of
green on different parts of one aircraft. That’s because yet again, different parts
makers use different formulas of zinc chromate or zinc phosphate. Notice how certain parts
of the green aircraft are not painted green, can you guess why? You will find out shortly.
During the assembly process the anti corrosion coating is usually damaged. Scratches and dents
result from various tools and assembly jigs which leave openings in the protective layers.
These scratches cannot be ignored as they would lead to future corrosions,
and thus painters have to frequently patch up the anti corrosion coating.
Prior to painting the aircraft, it’s better to remove the green coating altogether using
chemicals, wash the entire aircraft and inspect for corrosion, and then reapply the anti-corrosion
coating, and only then paint the aircraft, as you see happening to this Westjet Boeing 737.
But not all aircraft are painted.
The silver-looking airplanes that American Airlines flies are naked. Just bare metal.
Only the stripes and the logos are painted. Why is it that they don’t need the green coating?
The thing is, all modern airplanes are made from Alclad, which is a corrosion-resistant
material on its own. Alclad is made by applying a thin layer of pure aluminum over the entire
aluminum alloy. This layer then turns into aluminum oxide which is corrosion resistant.
The green coating is done to further protect an already corrosion-resistant material.
And guess what? Not painting the entire airplane means less overall weight, about 1200lb less,
which is equivalent to about 8 passengers, or 6 Americans, I’m joking of course … 3 Americans!
In the long run, not having to repaint the aircraft every 3 to 4 years,
and the fuel savings due to the weight reduction mean more profit for the airline.
But being naked has its own kind of maintenance! About 3 to 4 times a year,
the silver-looking aircraft has to be polished. Specifically, the aircraft must be thoroughly
washed and then buffed with a waterproof wax to further increase protection against corrosion.
For various reasons, American Airlines discontinued this bare metal look.
Some say the cost savings from the reduced weight didn’t materialize as the costs of
maintaining the bare metal was higher than anticipated. This suggested that using the
anti-corrosion layer and painting the jet would be cheaper than constantly buffing the bare metal.
Others say that American Airlines switched to a new livery for marketing reasons, because newer
aircraft are no longer made from aluminum, which means American Airlines could not have the same
shiny look on all of their airplanes. You see how the nose cone and parts of the tail and
wings are painted? That’s because those parts are made of composite materials, and not aluminum.
This brings us to the Boeing 787 Dreamliner, which is made of composite materials like carbon
fiber. Since composite materials are not prone to corrosion, they do not require the protective zinc
chromate coating. Instead, different parts of the Dreamliners are painted white from the start. One
of the many benefits of building the Dreamliners from composite materials, is to not have to worry
about corrosion. Additional benefits include a lighter structure, which results in fuel savings,
absence of metal fatigue which aluminum airplanes experience, and finally, improved cabin humidity.
But what if they didn’t paint the Dreamliners at all? A bare carbon-fiber look. Would that
result in black airplanes? Probably not, as only about 50% of 787
is made out of the composite materials, with the rest being aluminum, Titanium and Steel.
But have you noticed how there are so few black airplanes? A common misconception is that most
airplanes are not painted black, because black paint absorbs more sunlight than other colors,
which increases air conditioning costs. But at an altitude of 30,000 feet, the typical
air temperature is like -40 degrees, celsius to fahrenheit. The real reason is that black paint
fades away much faster than white paint, meaning that black airplanes would need to be repainted
more often, which adds cost. Also, scratches that result from daily operation of the aircraft are
much more visible on black paint compared to white paint. Take a look at any black car in
the parking lot and this should be evident. Another reason is that in case of emergency,
a white aircraft would be easier to spot than a black airplane. For one reason or another,
most airlines prefer white colored airplanes, and this is evident by the fact that an aircraft
painted in white has a better resale value. Of course, there are some airlines that
paint their aircraft black, but they do so purely for marketing reasons.
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