There are actually two kinds of skywriting: traditional and digital. The kind the Olivers do is traditional, or "longhand," and few people can do it. There's no official training program or certifying body; it's just something that's learned. Suzanne Asbury-Oliver learned from Jack Strayer, who was skywriting for Pepsi in 1980 when she answered the company's want ad for a second pilot [source: Smithsonian National Air and Space Museum]. Asbury-Oliver taught her husband [source: Spitznagel].
To write legibly on the sky, pilots have to maneuver quickly and accurately while moving at 150 mph (240 kph), pressed into the seat by G-forces [source: Hartill]. It takes 17 maneuvers in 10 minutes to write the five letters in "PEPSI" [source: Olivers Flying Circus]. And all the while, they have to, you know, fly a plane.
The writing process begins at around 10,000 feet (3,000 meters), where the air is calmer and cooler. Cooler air exerts more pressure, so it helps hold the smoke together. Since ground-based viewers are on the other side of the writing, skywriters need to draw the letters backward. (Add that to the skill set.)
It's kind of like drawing a picture in the dark. The pilots really can't see much. It's hard to make out the smoke against the sky, and the only orientation points are on the ground, which may or may not be in sight at any given time [sources: Asbury-Oliver, Hartill]. So they feel their way. They might count to 15 to get to the right length for an F's upright [source: Hartill]. What counts most is precision. "Either your headings, rates of turn and timing are exactly correct or it doesn't work," explains Asbury-Oliver. So the more curves and lines in a character, the greater the chance of messing it up. "Writing in Chinese," she says, "is tough."
Nature counts, too. "You don't write on a cloudy day," says Asbury-Oliver. "The 'smoke' is the same color as clouds, so you can't see it." Windy days are out, too. The message will dissolve before people can read it.
In ideal conditions, though – cool, humid, windless and clear – messages can hang around for 20 minutes or more, visible from up to 30 miles (50 kilometers) away [source: Library of Congress]. The messages average about eight characters long, with each letter about 1 mile (1.6 kilometers) tall [sources: [http://science.howstuffworks.com/transport/flight/modern/skywriting5.htm]Olivers Flying Circus, Sky-Writing.com]. The actual maximum a pilot can draw, though, depends on his or her plane.