HILO, Hawai'i — The latest episode of the Kilauea volcano eruption is offering the best daytime lava viewing opportunities for airborne tourists in years, and word has gotten around.

Air tour companies on the Big Island have seen a big boost in business thanks to the spectacular lava stream oozing toward the northeast from a fissure near Pu'u O'o, company representatives said. Recent clear weather is ensuring good visibility for the show.

The only way to see the flow is from the air, which means there has been "plenty of aviation activity" over the flow, said pilot Dale Scharpenberg of Hawai'i Island Hoppers. "I've been doing tours from Hilo for seven years, and this the best lava flow I've ever seen."

The flights travel along a stream of lava that extends for about four miles, moving rapidly as it emerges from its underground source, and slowing as it reaches the limit of the flow, he said.

Lava flows in recent years mostly moved through underground tube systems, but for the past six weeks most of the flow that surfaces northeast of Pu'u O'o is above ground, he said.

The lava emits an intense red glow at night, but is also clearly visible in the daytime.

Susan Costa, Hilo operations manager for Sunshine Helicopters Inc., said her company is booking about a day in advance because business has "really picked up." The company has dedicated a total of three helicopters to lava overflights, with some based in Hilo and some in South Kohala.

"I'd say 99 percent of the passengers that come off are just elated, because they can't believe what they've seen," she said.

"Truthfully, I've been doing this for 18 to 20 years ... and I haven't see this kind of stuff maybe in the last 15 years," she said of the flow.

The flow is edging generally toward populated areas around Pahoa, but scientists with the U.S. Geological Survey say there is no direct threat from the lava because the flow keeps stalling as the lava cools in the open trench.

To move much beyond the four miles the lava has already advanced from the fissure, scientists say the flow's volume would need to increase significantly, or the lava would have to shift to a sub-surface tube system.

If such a shift were to occur, that would allow the flow to stay hotter longer, and would allow it to cover more ground before it solidifies.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.