In Theodore Taylor's The Cay, Phillip and Timothy are stranded on an island (the cay referenced by the title) after the ship they were traveling on, the S.S. Hato, was torpedoed by a German submarine. In order to try to flag down passing airplanes which might rescue them, Timothy builds a large fire pile on the beach which can be lit with flames from a smaller fire in order to generate smoke to signal a plane. Timothy also spells out "HELP" on the ground with rocks, learning to spell the word through Phillip's instructions.
Unfortunately, the fire signal does not work; although planes do pass the area, they mistakenly believe the white smoke coming from the fire is just low-hanging clouds and do not further investigate. Sadly, Timothy dies after a hurricane batters the island, and Phillip alone is rescued by a navy ship one year after arriving on the cay.
In The Cay by Theodore Taylor, first Phillip and Timothy get somewhat settled in. Timothy builds a hut, tall enough that Phillip can stand up in it. He leaves Phillip to go to the reef and catch some langosta, so that they can eat. Timothy then makes a fire pile down on the beach. If, in the event, he and Philip hear an airplane, they also have a small fire smoldering at their campsite, so that they can take some lit wood from their fire to light the bigger one. Since Timothy cannot read and write, he asks Phillip to write "HELP" in the sand, and then Timothy fills in the lines with rocks. They are hopeful if an airplane flies overhead, the pilot will see the word and/or the smoke from the fire, and they will be rescued.