Becky Bohrer, AP

JUNEAU, Alaska (Aug. 14) -- The plane that crashed into an Alaskan mountainside and killed former Sen. Ted Stevens and four others was outfitted with an alert system that warned pilots of dangerous terrain.

But National Transportation Safety Board chairwoman Deborah Hersman said that it's not known if the system was working just before the plane crashed Monday.

The plane was also equipped with an emergency locator transmitter, Hersman said at a news conference in Anchorage Friday. When properly registered, it issues a distress signal to a control center via satellites and provides registration information, such as the owner's name. She added that it was also unclear why that signal didn't activate.

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 told reporters that one of the survivors described Monday afternoon's crash by saying: "They were flying along, and they just stopped flying."

The same survivor said he didn't notice any changes in the plane's pitch or hear any unusual engine sounds right before the plane went down about 20 miles north of Dillingham in southwest Alaska.

Hersman didn't identify the survivors who spoke with officials.

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

An Anchorage hospital on Friday upgraded Sean O'Keefe from critical to serious condition. Kevin O'Keefe remained in fair condition, Morhard also was in fair condition and Phillips was in good condition.

Also killed were pilot Theron Smith, General Communications Inc. executive, Dana Tindall, Tindall's 16-year-old daughter, Corey, and William "Bill" Phillips Sr., who had worked with Stevens in Washington.

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.

GCI spokesman David Morris said about 13 people originally came to the lodge Aug. 7 for what was "primarily a Stevens trip."

For years, the 86-year-old Stevens used GCI's lodge to show politicians and regulators what life in rural Alaska was like.

Smith was a temporary replacement for the regular pilot, who had unexpectedly quit, Morris said. Smith was a longtime pilot for Alaska Airlines - retiring in 2007 after 28 years - and was qualified to fly the float plane and to fly in that part of the country, Morris said.

Hersman said Smith was estimated to have had 10 hours of air time in the float plane that crashed and another 35 hours in the same type of plane. He had thousands of hours in both single and dual engine amphibious aircraft.

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.

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 out as a possible cause, Hersman said.

Associated Press Writers Rachel D'Oro, Mary Pemberton and Mark Thiessen in Anchorage, Alaska, and AP News Researcher Julie Reed Bell in Charlotte, N.C., contributed to this report.