Investigators are examining whether rain, wind and cloudy skies contributed to the Alaska plane crash that killed former Alaska Senator Ted Stevens.
The plane carrying nine people crashed near Dillingham, Alaska on Monday while en route to a fishing trip.
Former Nasa chief Sean O'Keefe, who was also on the plane, survived the crash, but remains in critical condition. His teenage son suffered serious injuries.
The crash left five dead and four injured.
Flights near Dillingham can be risky even in good weather, media reports suggest.
National Transportation Safety Board chairwoman Deborah Hersman said there was light rain, clouds and gusty winds at the time of the crash.
But Ms Herman said the federal investigation was still in its early stages and it was too soon to determine what caused the accident.
"We're certainly looking at weather, but everything's on the table right now and we haven't ruled anything out," Ms Hersman told the CNN TV network.
Investigators have yet to speak to crash survivors, Ms Herman said.
Three teenagers and their parents were on the plane, which a Federal Aviation Administration spokesman has named as a 1957 DeHavilland DHC-3T.
Officials say rescue and recovery efforts were slowed by bad weather.
The alarm was raised on Monday evening when the plane, which was registered to Anchorage-based General Communications Incorporated (CGI), failed to land on schedule.
Shortly afterwards, local residents spotted the wreckage on the side of a mountain about 17 miles (27km) north of Dillingham.
Spokesman Mike Fergus said the plane had been headed to Agulowak Lodge on Lake Aleknagik from a site owned by GCI on Lake Nerka.
Harsh weather conditions hindered the rescue effort until early the next morning, when Alaska National Guard used helicopter hoists to rescue four survivors.
Several local people had reached the wreckage before rescuers could arrive and tended to the survivors, officials said. The survivors were then flown to Anchorage.
A gruesome night
A pilot, who was one of the first to respond to the crash, described a horrific scene of plane wreckage, spilt fuel, dead bodies, rainy weather and terrified survivors.
The former Republican senator, who was remembered as having brought billions of dollars to Alaska during his 40 years in the US Senate, was lying dead in the plane's fuselage when crews arrived, the pilot said.
Responders at the scene spent the night scrambling over the fuel-coated mountainside while trying to keep the crash survivors warm and tend to their injuries.
Temperatures near Dillingham ranged from 48-50F (8-10C) on Monday night .
"These individuals were cold. We covered them up with blankets and made them as comfortable as we could," rescue worker Tom Tucker told the Associated Press news agency.
When crews arrived, one survivor was still sitting in the front seat of the plane with his seatbelt on - despite the plane's nose being disintegrated.
The man's legs appeared to be broken and his head was cut.
"The front of the aircraft was gone. He was just sitting in the chair," said Mr Tucker, who helped transport a doctor and emergency crew to the scene three hours after the accident.
Mr Tucker said he and other workers used a tarp to make a tent over the cockpit to protect the survivor from the elements.
Mr Stevens was the longest-serving Republican in the history of the Senate, having been appointed to the body in 1968 and won election two years later.
One of his best-known projects - known as the "Bridge to Nowhere" - was the focus of criticism by US groups who queried the more than $400m (£252m) price tag for the bridge's construction, noting it was to serve only a tiny population on an isolated island.
Mr Stevens was one of two survivors of a 1978 plane crash at Anchorage International Airport in Alaska that killed his wife, Ann, and several others.
Mr O'Keefe led Nasa from December 2001 to February 2005, having been nominated for the position by President George W Bush.
His tenure at the space agency was marked by major accomplishments, such as landing the two Mars Exploration Rovers on the surface of the Red Planet.
Monday's plane crash was the third in less than two weeks in the state.