The cause was heart failure, his son, Hans, said.
A commercial 747 bound from New York to Seoul, South Korea, KAL 007 was shot down near Sakhalin Island, off the coast of Siberia, on Sept. 1, 1983, after straying accidentally into Soviet air space. All 269 people aboard were killed.
The Soviet Union long maintained that the flight was a spy plane sent by the United States, and the attack endures in public memory as one of the last, bitterest engagements of the cold war.
Afterward, Mr. Ephraimson-Abt was in the vanguard of establishing a unified movement to aid air-crash victims' families. In work that occupied him to the end of his life, he traveled the world, testifying, lobbying and meeting with government officials, airline executives and bereaved families.
"Hans fought for people who didn't have a voice and didn't know that they needed a voice," Deborah A. P. Hersman, the chairwoman of the National Transportation Safety Board, said in a telephone interview. "He turned his own tragedy into advocating for all air travelers, to make sure that their families were taken care of and treated with respect after an accident."
Mr. Ephraimson-Abt, who was fluent in a string of European languages, assisted not only the families of KAL 007 passengers, but also those of victims of many later crashes, including Pan Am Flight 103, which was destroyed by a bomb over Lockerbie, Scotland, in 1988.
After the Sept. 11 attacks, he advised relatives of passengers aboard the hijacked planes, in particular the families of passengers from Germany, where he was born and brought up.
Mr. Ephraimson-Abt was the longtime chairman of what was known early on as the American Association for Families of KAL 007 Victims; reflecting its expanded purview, the association more recently became the Air Crash Victims Families Group, of which he was the spokesman.
In 1983, when KAL 007 families chose to band together after the crash, there were few avenues for obtaining support. Responding to air crashes from notifying relatives and keeping them abreast of recovery efforts to providing emotional assistance was then the duty of the airlines, a state of affairs that in the view of Mr. Ephraimson-Abt and his colleagues needed to be remedied.
In the 30 years since, as a result of their work, significant advances on behalf of victims' families have been made.
In 1996, Congress passed the Aviation Disaster Family Assistance Act, which empowered the National Transportation Safety Board to notify the families and the Red Cross to help care for them.
The next year, a new international aviation agreement raised the amount for which an air carrier was liable when an international flight crashed. The previous limit, set in 1966, capped carriers' liability at $75,000 per passenger, except in rare cases where families could prove the airline guilty of willful misconduct.
The 1997 agreement, which Mr. Ephraimson-Abt helped broker, raised the cap to $139,000. For families seeking greater damages, the new agreement also relieved them of the burden of proving willful misconduct.
Near midnight on Aug. 30, 1983, a 23-year-old Alice Ephraimson-Abt boarded KAL Flight 007 at John F. Kennedy International Airport. A recent graduate of Wittenberg University in Springfield, Ohio, where she had majored in East Asian studies, she was headed, via Seoul and then Hong Kong, to Beijing. In China, she planned to teach English and study Mandarin.
After a refueling stop in Alaska on Aug. 31, Flight 007 took off for Seoul. By the time it was spotted by the Soviets on Sept. 1, it had deviated hundreds of miles off course.
After the plane was shot down, many victims' families were not notified directly. Mr. Ephraimson-Abt heard about the crash from a hotel manager in Hong Kong, whom he had enlisted to look after his daughter on her arrival there.
Mr. Ephraimson-Abt immediately phoned Korean Air Lines. The airline, he said afterward, hung up on him.
"To this day," he said in 1996, testifying before the Senate Commerce, Science and Transportation Committee, "Korean Air Lines has not informed me of the death of my daughter."
On Wednesday, Mr. Ephraimson-Abt's son said that to his knowledge, the airline had still not communicated with the family.