The three survivors also are Americans, including a Utah businessman who was pulled from the wreckage by farmers shortly before it exploded Sunday in a field lined with palm trees.
"We only know the engine had problems and they did not make a successful landing," Swain said Monday.
The single-engine Cessna Caravan, also known as a Cargomaster, broke apart and scattered burned wreckage across a barren field where the pilot made an emergency landing about 60 miles east of Guatemala City, Guatemalan civil aviation director Jose Carlos said.
Johnson was prepared to fly to Guatemala when he got a message from the U.S. Embassy in Guatemala City that his wife, Liz, a leader on the expedition, had died, Swain said. Liz Johnson died at 3:15 a.m. Monday, said William Diaz, general manager of Hospital El Pilar in Guatemala City.
Johnson decided to stay in Utah, where he remained in mourning Monday.
"There's not a thing he can do at this point. We're working with the U.S. Embassy to have all of the arrangements made for the repatriation of those who are deceased, and medical flights for those living," Swain said.
The embassy did not immediately return calls seeking comment. CHOICE Humanitarian is aimed at helping people in poverty around the world improve their own lives. CHOICE stands for the Center for Humanitarian Outreach and Inter-Cultural Exchange.
The group relies on help from volunteers who pay their own way on trips to countries including Guatemala, Mexico, Bolivia, Nepal and Kenya. The volunteers on the flight that crashed were on their way to a Guatemalan town called Sepamac.
Among the dead were Roger Jensen and his son, Zachary, of Amery, Wis. A daughter, Sarah Jensen, 19, suffered minor cuts and bruises and survived along with her mother, April, who had burns and contusions, Sarah Jensen told the AP in a brief hospital interview.
April and Sarah Jensen were expected to return Monday to the U.S. by air ambulance, said Diaz, the hospital official.
The Guatemalans who died in crash include pilot Fernando Estrada; co-pilot Monica Bonilla; and two CHOICE Humanitarian representatives in Guatemala, Javier Rabanales and Walfred de Rabanales, according to civil aviation authorities and Swain. Utah businessman Dan Liljenquist survived the crash with a broken right leg and broken left ankle.
"There were farmers in the field where they crashed. They pulled my husband out of the plane 30 seconds before the plane exploded," Brooke Liljenquist told the AP in a telephone interview from her home in Bountiful, Utah.
"He has constant pain he says he can deal with. He's just grateful to be alive," she said.
Dan Liljenquist is president and chief operating officer of Focus Services of Roy, Utah, which handles customer service calls for other companies. Brooke Liljenquist said the crash killed four employees of his company, two from Utah and two from another call center in Cedar Falls, Iowa.
The other U.S. passengers who died were Cody Odekirk; John Carter; Jeff Reppe and Lydia Silvia, according to Guatemala's civil aviation authority, which didn't list their hometowns. Swain declined to provide that information.
Roger Jensen, 48, was the maintenance manager at Smyth Companies in St. Paul, Minn., for 12 years, Chief Executive Officer John Hickey said Monday.
"He did everything. He was a carpenter. A multipurpose utility player. He was a very popular employee, forever upbeat," Hickey said. "He was very giving. I think he was in Africa last year."
Hickey said Jensen helped pay for his family's trip by recovering copper pipe from a facility being closed by the company, which prints consumer product labels.
"We thought the world of this guy," he said. "He was just a bright light in the company."
Associated Press writers Juan Carlos Llorca in Guatemala City and Robert Imrie in Wausau, Wis., contributed to this report.