NTSB: Plane with Stevens had danger alert system

But it's not clear if the system was working just before the plane hit a steep, rugged mountainside, killing Stevens -- the longest-serving Republican senator in U.S. history -- and four others, chairwoman Deborah Hersman said at a news conference in Anchorage.

The five victims died from blunt-force trauma, state medical examiner Dr. Katherine Raven said. Four people survived, and investigators interviewed two of them on Friday.

Hersman didn't identify the survivors who spoke with officials on Friday. She did not say why she wasn't naming the two who were interviewed.

Former NASA chief Sean O'Keefe, his son, Kevin O'Keefe, lobbyist Jim Morhard and lobbyist William "Willy" Phillips Jr. lived through the crash.

Hersman said one survivor recalled that the group decided during lunch at the GCI-owned lodge to head to the fishing camp, a trip that had been put off in the morning due to poor weather.

The survivor said conditions had improved by the afternoon. He said he fell asleep about 10-15 minutes into the flight and woke up after the crash, Hersman said.

Authorities have said that, had the most direct route been taken, the crash would have occurred about 15-20 minutes after takeoff, but it wasn't yet clear if that's the path that was taken.

Hersman said Smith didn't request a weather briefing before departure. However, investigators have been told there was Internet service at the camp and he may have checked conditions that way.

Camp guide Byron Orth said the lodge called to say the group was heading to the camp. But when no one showed up, Orth figured the trip had been canceled. Hours later, the lodge called the camp and asked if Stevens' group was on its way back.

Orth said people at the camp and lodge feared the worst had happened.

"You're hoping for the best, but there's a bad feeling in your stomach," he said.

Investigators have been examining the pilot's log book, weather information and the mechanics of the plane. Other officials were working to bring the wreckage off the hillside for closer inspection at a hangar.

Nothing has been ruled anything out as a possible cause, Hersman said.

The plane was also equipped with an emergency locator transmitter, she said. When properly registered, it issues a distress signal to a control center via satellites and provides registration information, such as the owner's name.

But because the injuries sustained were "severe and fatal," a quicker response from rescuers probably wouldn't have made a difference, said Raven, the medical examiner.