HAWAII ISLAND (KHNL) - It's been more than 24 hours since a cessna plane has gone missing on the Big Island.
Search efforts have covered offshore waters to the mountains. Now, the search has become more focused. Crews are not only looking for any signs of the plane, they are also listening for any signal from the plane's emergency equipment.
Planes are required to carry an emergency locator transmitter or ELT, which can be activated to let rescuers know where to look.
According to the FAA, the missing plane's ELT was not activated.
But on Tuesday, Coast Guard crews heard something.
As the sun came up, so did a Coast Guard helicopter just one of a dozen aircraft involved in the day's effort.
The missing plane, operated, by Island Hoppers Tours, left Tuesday morning from Kona but never returned.
The Cessena carried a pilot and two passengers for a tour of the Big Island.
24 hours after the plane was due in, emergency crews have already searched 2500 square miles, an area about 4 times the size of Oahu.
While planes and helicopters flew overhead, emergency operations are coordinated on the ground. Along with search efforts underway in the hawaii volcanoes national park.
And it is the southern side of the Big Island where the search is concentrated.
"The Kau Forest is densely rugged with lots of canyons and crevices. A lot of areas where a plane could be missing." says Lt. John Titchen, with the US Coast Guard.
This is not the first time search crews have been called in to look for an Island Hopper plane.
In 2004, a single engine piper went down in a South Kona lava field. It took emergency crews nearly five hours to find the plane and its badly burned passengers, because rain and darkness slowed the search.
But in this day's effort, visibility is good, with mostly clear skies. And even a glimmer of hope in the hunt for the missing plane.
"We did get a very weak faint signal very early this morning. We're not confident that it is the ELT aboard this particular aircraft." says Titchen.
But that emergency transmitter was too faint to lead crews to the plane.