An Oregon mother is clinging to faint hope that her two daughters and their father are still alive after their jetliner vanished somewhere over Indonesia on New Year's Day.
The missing Boeing 737, en route from Jakarta, Indonesia, with 102 people aboard, disappeared from radar screens Monday night after the pilot twice altered the flight path due to strong winds. Search efforts as of Friday had found no trace of the plane or its passengers.
Lindsay and Stephanie Jackson, 18 and 21, and their father Scott, 54, of Bend, Ore., were the only three Americans known to be on board the airliner.
The girls, who are students at the University of Oregon, traveled to Indonesia during winter break to visit their father, who is president of an Indonesian manufacturing company that makes rattan furniture. Their brother Greg Jackson, 20, joined them, but he returned to Oregon last week.
The family members are no strangers to travel.
The girls' mother, Felice Jackson DuBois, who is divorced from Scott, described her daughters as adventurers who have lived and traveled overseas since they were born.
"Any time I hear that they're going on an airplane, yes, I'm scared," DuBois told The Oregonian newspaper. "But you can't live your life guided by your fears. You just want to hold out hope."
Lindsay is majoring in biology through the university's Clark Honors program, and Stephanie is a senior double-majoring in human physiology and anthropology, a spokesman for the University of Oregon told FOX News.
DuBois described Stephanie as "tenacious," and recalled a time when the family was living in the Portland suburb of West Linn. A stack of freshly cut oak was sitting in front of their house, and her father told Stephanie, then in first grade, that she should try to sell it.
"She went out and sat on that pile of wood with a for-sale sign the entire day," DuBois said. "She sold it all. Whenever you would give her something, she was like a dog with a bone. She just wouldn't let up on it."
Lindsey Jackson, meanwhile, has always been a nature lover, and wanted to be a veterinarian as a child.
"There'd be a butterfly here, a beetle there," DuBois said. "We always say that animals don't understand that she's human. She had an affinity for the natural world, and we always said she was a walking insectorium."
The Jackson sisters graduated from Summit High School in Bend. Both ran cross-country and Lindsey Jackson threw the javelin for the team, coach Dave Turnbull told The Bulletin newspaper of Bend.
"There are some kids out there who everybody likes because they're genuine, they're sincere," Turnbull said. "They were good athletes and good kids."
In her high school yearbook, Lindsey Jackson wrote that her future plans were to: "Solve world hunger by living on a boat studying the ocean."
As a young couple, Felice and Scott lived in places that included Borneo, Indonesia, Guyana and Brazil, DuBois told The Oregonian.
Once, while they were residing in Brazil, Scott Jackson was held hostage by wood-products workers who were angry about their working conditions. Another time, the couple was on-board an airplane that was hijacked in Hong Kong.
DuBois recalled flying in various planes that ran into problems over dense jungles, oceans and other rough terrain. "I think we stretched our luck to the limit," she said.
Authorities expanded their sea search further south towards Bali on Friday, as U.S. investigators arrived in Indonesia to look into the apparent crash. It remained unclear what may have caused a crash, and investigators are unsure as to why there have been no transmissions from the plane's emergency locator.
The plane sent out two distress signals in stormy weather Monday halfway through its two-hour journey from Indonesia's main island of Java to Manado.
Initially, officials said 12 people had been found alive at a crash site on Sulawesi's mountainous western coast. But rescue teams hiking into the rain-soaked jungle found nothing. The government later recanted the reports, saying the earlier statements had been based on the unconfirmed accounts of villagers.
Around 50 angry protesters gathered in the capital, Jakarta, dressed like bloodied air-crash victims, calling for the resignation of the transport minister who took more than 10 hours to admit that reports of survivors were unfounded.
Authorities at the University of Oregon continue to await further news of the flight and the status of the girls.
"Obviously our hearts go out to family members and friends of the girls here on campus," said Phil Weiler, spokesman for the university." It's a time of uncertainty for everybody."
But the girls' mom continues to hold out hope.
"It's hard to ferret out the rumor from the facts," DuBois said. "All we can do is wait."
FOX News.com's Hannah Sentenac and the Associated Press contributed to this report.