(CNN) -- Federal investigators, joined by local officials and others, spread across Alaska on Thursday seeking the cause of a plane crash that killed five people, including former U.S. Sen. Ted Stevens.
Deborah Hersman, the chairman of the National Transportation Safety Board, told reporters that the initial investigation of the crashed airplane was complete. The wreckage would be hauled to nearby Dillingham, Alaska, to be examined further, Hersman said.
There was no new information on what caused the plane to crash Monday on a rugged mountainside in southwestern Alaska, killing Stevens and four others. Another four passengers survived, including former NASA head Sean O'Keefe.
Stevens, who served in the U.S. Senate for 40 years, was 86. His funeral will be held next Wednesday at 2 p.m. (6 p.m. ET) at the Anchorage Baptist Temple in Anchorage, according to Jim Manley, a spokesman for Senate Majority Leader Harry Reid.
O'Keefe remained in critical condition on Thursday, according to Kirsten Schultz, a spokeswoman for Providence Alaska Medical Center. The condition of O'Keefe's son, Kevin, was upgraded to fair from serious.
Another survivor, lobbyist Jim Morhard of Alexandria, Virginia, was also upgraded to fair from serious.
Thirteen year-old William Phillips, whose father died in the crash, remained in good condition, Schultz said.
A CNN reporter who flew over the crash site Thursday said there was a wide, brown swath cut through the trees by the plane. The crash occurred about 1,000 feet up the 2,300-foot mountain in an area called Muklung Hills, about a 20-minute flight from Dillingham, the reporter said.
Hersman said the de Havilland DHC-3 Otter involved in the crash was manufactured in 1957 and overhauled in 2005 from a piston to a turbine engine.
She also confirmed the plane lacked either a Ground Proximity Warning System or an Enhanced Ground Proximity Warning System. The devices, which Hersman said are not required, help pilots determine how far they are above ground or terrain and can predict whether a plane is on a path toward an obstacle or mountains.
Hersman said it was too soon to know whether any technological factor contributed to the crash.
John Bouker, the commercial pilot who first spotted the crash site, told CNN Thursday that Stevens' plane "was messed up but not beyond survivability."
"It looked survivable," Bouker said, "but it didn't look like it would be a very fun ride or anything. The wings were bent back. The nose section was messed up. It didn't look like a good situation to be in, that's for sure."
The aircraft, which was taking the group on a fishing trip, crashed in an area near the Bering Sea noted for its rugged terrain.
Tom Tucker, a helicopter pilot who landed at the crash site, told CNN that when he first arrived, the survivors "were coming in and out of consciousness. We put blankets over them to keep them warm."
The longest-serving Republican senator in U.S. history, Stevens lost his 2008 re-election bid to then-Anchorage Mayor Mark Begich after being convicted on charges of making false statements on financial disclosure forms.
A federal judge later dismissed the conviction, citing prosecutorial misconduct.
Stevens survived a plane crash that killed his wife in 1978; he later remarried.
CNN's Patrick Oppmann and Paul Vercammen contributed to this report