The engineer behind Abby Sunderland's solo trip around the world says he believes the 16-year-old Thousand Oaks sailor is "alive" and "most likely floating" in the middle of the Indian Ocean.

Speaking to a throng of reporters outside the family's home, Jeff Casher said he spoke to her at 3:45 a.m. Thursday, then lost contact after she went to check on some equipment on her boat. About an hour later, she apparently activated her emergency beacons – devices that sent automatic alerts to the Coast Guard and her family.

Casher said the family is looking at three possible scenarios. Either the boat's mast came down, giving her no ability to sail the vessel; the keel hit something and possibly flipped the boat upside down; or she may have broken an arm or leg while being whipsawed about in violent waters.

"She set this off not because she lost communication, but because something else was wrong," Casher said. They had set very clear guidelines for when to activate emergency beacons – and losing communication alone was not enough, he said.

Casher said the high school junior has the mental fitness to make it through this. Her brother, Zac, made a solo trip around the world when he was 17.

Abby Sunderland apparently was a little rattled when the boat's motor wouldn't work Thursday morning. But, Casher said, "The moment the engine started, she was her same old self – perky and tough.… She's just as tough, or tougher, as most of the cruisers we've met."

The family is hopeful that a Qantas Airbus, commissioned by the Australian government, will be able to spot her at daylight – about 10 or 11 p.m. Pacific time.

Water temperatures are about 54 or 55 degrees, Cash said, describing it as cold, but survivable. Sunderland had equipment on board to survive a crisis, including a dry suit and life boat.

--Catherine Saillant in Thousand Oaks and Rich Connell in Los Angeles