HILO, Hawai'i — A sharp-eyed 15-year-old boy on an afternoon tour flight spotted a flash of light from a hilltop in a lava field yesterday, and that led to the rescue of a stranded hiker who had been missing since Sunday night.

A crew from Blue Hawaiian Helicopters picked up Gilbert Dewey Gaedcke shortly after 4:30 p.m. and delivered him to a waiting ambulance at the Hilo airport.

Fire Capt. Darren Rosario of the Waiakea Fire Station said the 41-year-old computer consultant from Austin, Texas, was dehydrated but otherwise in good shape.

Gaedcke, an experienced outdoorsman, was taken to Hilo Medical Center, Rosario said.

"It didn't look good at the beginning of the week, but we were really happy with the way it turned out today," Rosario said. "The family is ecstatic."

Peter Frank, 15, of Pasadena, Calif., was sitting in the rear seat on a helicopter tour flight from Waikoloa with his family when he noticed something shining from the vegetation on an overgrown hilltop jutting out of a blackened lava field. The helicopter was traveling at about 1,000 feet and had just completed a tour of the area around Kilauea volcano.

Peter picked up the cabin microphone and asked the pilot what the flashing light was. "He didn't know what it was, so he circled around that little mound he was on, and then we realized it was a person," Peter said.

The figure on the ground was a man in a blue shirt and long pants who used a mirror or other shiny object to signal the aircraft. He also shook small trees and waved his arms to try to get the attention of the pilot and passengers, Peter said.

Pilot Cliff Muzzio said Gaedcke "was obviously not real hurt or anything, but he looked frantic."

Once Gaedcke knew he had been seen by the circling helicopter, he sat down and "sort of collapsed," said Peter's mother, Diann Kim. "He just appeared exhausted."

Peter's family members stuffed water bottles into air-sickness bags to pad them, and the pilot then hovered low enough to toss the water out the window to Gaedcke, Peter said.

Muzzio radioed to notify authorities, but was told Fire Department helicopters normally used for rescues were fighting a large brushfire in Kohala.

Muzzio, 48, then flew to Hilo to let off Peter and his family, and returned to the scene 17 miles south of Hilo with another Blue Hawaiian employee to pick up Gaedcke.

Gaedcke, who had left the Kalani Honua Retreat in rural Puna at 9:30 p.m. Sunday, was reported missing the following morning. His car was later found at the old lava flow at the end of Kalapana Road, and the keys were found near the car, police said.

Gaedcke told fire crews he missed reaching his car as he hiked back toward it late Sunday night and continued walking inland. After about two days, he said, he built a makeshift camp and was able to find enough fresh water to survive.

Firefighters from the Waiakea station and crews from Hawai'i Volcanoes National Park had conducted daytime ground searches since Tuesday. Helicopters also had been called in.

Richard Koob, director of the Kalani Honua Retreat, said Gaedcke mentioned to cafeteria workers on Sunday that he wanted to observe Kilauea's flowing lava. He even bought a flashlight at the gift shop.

But employees tried to dissuade Gaedcke from going out that night alone because of the risks of walking in a dark, remote area on uneven, solidified lava.

"That's not the kind of thing you do on your own," Koob said. "We don't recommend that."