DILLINGHAM, Alaska (AP) — A pilot who spotted the wreckage of the amphibious plane carrying former Sen. Ted Stevens looked down on the gashed mountainside and thought that no one could’ve survived such a crash.

Then, he heard another pilot say on the radio: A hand was waving for help from a window of the red-and-white aircraft.

‘‘It surprised me because I didn’t think it was survivable,’’ said Eric Shade, 48, owner of Shannon’s Air Taxi.

The discovery set in a motion a frantic rescue effort that culminated when National Guardsmen had the four dazed survivors, suffering from broken bones and other injuries, airlifted off the mountain. Five others, including the state’s most revered politician, were dead.

A fishing trip that Stevens and his friends have made for years to a southwest Alaska lodge — sometimes drawing criticism for hosting lobbyists and lawmakers there to discuss government issues — had ended in tragedy and left family searching for answers.

The cause of the crash was being investigated on Wednesday as National Transportation Safety Board officials hiked to the scene and began examining the wreckage, chairwoman Deborah Hersman said. They had hoped to interview the survivors Wednesday in the hospital but their medical conditions made it impossible.

Officials said a technology that Stevens had long pushed to improve air safety in Alaska wasn’t installed in the downed plane. It was unclear whether the instruments would’ve prevented the Monday crash.

Several medical volunteers who scrambled up the boulder-strewn slopes to the crash site found survivors trapped inside the fuselage, with one still strapped into the co-pilot seat. Rescuers had to cut alders to reach survivors, and then ripped open the plane to get them out.

‘‘They didn’t do too much talking with us,’’ said Alaska Air National Guard Senior Master Sgt. Jonathan Davis, one of the rescuers lowered onto the mountain from a helicopter. ‘‘If they did talk, they were asking for pain medication, and we helped them with that.’’

Stevens, 86, had close ties to everyone on the plane, including Anchorage-based General Communications Inc., a phone and Internet company that owned the aircraft, and the lodge where the passengers were staying.

‘‘These were old friends who stayed in touch and loved him,’’ said Stevens’ friend, Russ Withers.

GCI frequently hosted high-profile guests, politicians and regulators at the Agulowak Lodge on Lake Aleknagik for fishing trips, drawing scrutiny from Alaska lawmakers over whether the expeditions violated ethics rules.

At a hearing in 2002, lawmakers grilled GCI executive Dana Tindall, who died in the crash, about the trips.

Tindall testified that Stevens and William ‘‘Bill’’ Phillips Sr., who also died in the wreck, once arranged for a staff member to travel to the lodge to learn about the telecommunications world as GCI looked to expand its business.

‘‘We entertain business associates. We entertain — there have been FCC commissioners out there. And there have been members of the United States Congress out there,’’ Tindall told lawmakers.

Stevens and ex-NASA chief Sean O’Keefe, who was also on the plane and survived, were fishing companions and longtime Washington colleagues who worked together on the Senate Appropriations Committee led by the GOP lawmaker. Stevens became a mentor to him.

Phillips and Jim Morhard, who survived the crash, also worked with him in Washington. Morhard founded a lobbying firm. Phillips was a lobbyist.

Authorities said the group boarded the 1957 float plane sometime Monday afternoon for a trip to a salmon fishing camp.

Lodge operators called the fish camp at 6 p.m. to inquire when the party would be returning for dinner, but were told that they never showed up. Civilian aircraft were dispatched, and pilots quickly spotted the wreckage a few miles from the lodge, authorities said.

A doctor and EMTs were flown to the area and hiked to the wreckage as fog and rain blanketed the area and nightfall set in, making it impossible for rescue officials to reach the scene until daybreak.

Tom Tucker, who helped shuttle the medical workers to the scene, described seeing a survivor still strapped in the front seat with the nose of the plane in shambles. His head was cut, and his legs appeared to be broken.

‘‘The front of the aircraft was gone,’’ Tucker said. ‘‘He was just sitting in the chair.’’

He and the other responders made a tarp tent over the missing cockpit to keep him dry. It was rainy and cold, and he believes the passengers’ heavy duty waders protected them when they went into shock. Temperatures ranged from about 48 degrees to 50 degrees overnight at Dillingham.

Plane crashes in Alaska are common because of the treacherous weather and mountainous terrain. More than 80 percent of Alaska’s communities, including the state capital of Juneau, are not connected to highways or road systems, making travel by air an essential.

The aviation dangers have prompted federal officials to push for more airplanes to be equipped with a new technology that provides pilots with better weather information.

Federal Aviation Administration chief Randy Babbitt in June credited the technology — a surveillance system intended in part to help pilots have a greater sense of awareness when they’re nearing bad weather — with ‘‘making a real difference’’ in air safety in Alaska.

The plane Stevens was on was not outfitted with that technology, Jim La Belle, regional director for the NTSB, told The Associated Press. He declined further comment, deferring to the investigative team.

The technology, hailed by the FAA as ‘‘the future of air traffic control,’’ is called Automatic Dependent Surveillance-Broadcast. It’s meant to help replace the radar that pilots and controllers now rely on with GPS technology.

The system can cost from $7,600 to $10,900 to equip a general aviation aircraft, FAA spokeswoman Tammy Jones said. Plans currently call for all aircraft flying within certain controlled air space to be equipped with the technology by 2020, she said.

Alaska was one of the first test sites for the program. In June, FAA said that, under the Capstone project, it has equipped ‘‘hundreds of general aviation aircraft’’ in southeast Alaska with the technology.

The other people who died are: pilot Theron ‘‘Terry’’ Smith, 62, of Eagle River; and Tindall’s 16-year-old daughter, Corey. Authorities said autopsies were performed on all five victims and a toxicology screen was performed on the pilot, both standard procedures. Results weren’t immediately available.

In addition to O’Keefe, his son Kevin and Morhard, the other survivor was Phillips’ son, William ‘‘Willy’’ Phillips Jr., 13. He was in good condition.

Paul Pastorek, who’s acting as a spokesman for the O’Keefe family, said in a statement Wednesday that the injuries to O’Keefe and his son don’t appear life-threatening, ‘‘and we are confident they will have a full recovery.’’ The younger O’Keefe attends Syracuse University.

Stevens was a legend in his home state, where he was known as ‘‘Uncle Ted.’’ The wiry octogenarian was appointed in December 1968 and became the longest-serving Republican in Senate history. He brought billions of federal dollars home for projects.