Dr. Charles D. Snelling and his wife Adrienne. (Cedar Crest College)

Three years ago, Adrienne Snelling wrote letters to her children and grandchildren explaining how she and her husband, Charles D. Snelling, decided to cope with her Alzheimer’s disease.

Adrienne was 79 then and had been battling the illness for about four years. Charles, her husband of nearly 60 years, was her primary caretaker at their home in Fogelsville, Pa. She was an accomplished fine arts photographer; he was prominent in Republican circles and had recently stepped down as chairman of the authority overseeing Reagan and Dulles airports and the construction of Metro’s new $6 billion Silver Line.

“As you know I have Alzheimer’s. It is not a nice disease. So far I have held up pretty well. Dad and I are still having a pretty good life. There is no doubt where my sickness will end up for me,” Adrienne wrote in the Nov. 22, 2009, letter.

She went on: “All of our lives, Dad and I have talked over our end of life beliefs. We are both in agreement that neither one of us wants to live after all reasonable hope for a good life is over. . . . We have had such a great life together and with all of you.”

On Thursday, just over a week after their 61st wedding anniversary, Charles took his own life and his wife’s in their home, police and airport authority officials said. He shot himself, authorities said. They have not said how she died.

One of the couple’s children, Marjorie Snelling, 56, of Philadelphia, said Friday that she knew her parents had talked about a plan to end their lives but that she and her siblings were stunned that it actually happened. There had not been “any specific signs.”

Still, she said, her family believes the pair “were deliberate and thoughtful.”

“They had a plan, and they were going to execute that plan without people knowing,” Marjorie said. “They’ve seen their peers and friends languish. . . . They had really been thinking about this for some time and keeping it a secret.”

Charles, who had a pacemaker and had undergone two knee replacements, was his wife’s main caregiver, although he had hired helpers who came in about 14 hours a day, friends and relatives said. “They were always deeply committed to each other,” Marjorie said. “They had a fundamental bond. We always knew they were united at their core.”

Courting Adrienne

That romance began when they met at a prom at Cedar Crest College, in Pennsylvania. Both were with other people at the time, but in a December 2011 column in the New York Times, Charles described his wife as a “simply marvelous young lady: ravishingly beautiful, bright, well-groomed, well-spoken, mannerly, disciplined and circumspect.” He “pursued her with all the vigor at my command.” He courted her by pretending to study with her at a park. They were married on March 21, 1951, the first day of their spring break, and went off for a quick honeymoon in Bermuda. The two had five children — one every two years over the early years of their marriage — and 11 grandchildren.

Adrienne, the daughter of a talented Italian marble craftsman, graduated from Cedar Crest, and photos she took appeared in two books. She later served on the Pennsylvania Council for the Arts.

Charles was born into a successful family, the son of Walter O. Snelling, an aristocrat and scientist who invented ways to better use gasoline; he sold a patent to John D. Rockefeller for $200,000 in 1910. Charles told of having 16-cylinder Chryslers and Packards and traveling often as a child.

Charles, a 1954 Lehigh University graduate, went on to have a vibrant career. He worked as an engineer and inventor and dabbled in real estate, running an orchard and a chain of restaurants. He held 20 issued patents and founded Cryo-Therm, a company in the thermodynamic energy-storage business.

Over the years, he served as four-time president of the Allentown City Council and finance chairman of the Republican Party in Pennsylvania. He was appointed to the Metropolitan Washington Airports Authority board in 2003 by President George W. Bush and was chairman from January 2010 to December 2011.

Even as he oversaw the board — with intense debates over a Dulles Airport Metro stop — Adrienne was never far away. He often would bring her and her caregivers with him when he traveled to the Washington area.

“You could tell above everything else they were the best of friends,” said Mame Reiley, a longtime friend of the Snellings who also recently stepped down from the airports authority board.

Reiley recalled that she had scheduled a dinner with Charles on Feb. 14 at the Ritz-Carlton in Pentagon City. It was the night before an airports authority board meeting, and he and Reiley often got together to discuss business.

When Reiley realized that it was Valentine’s Day, she called Charles to say they didn’t have to meet. He told her, no, he wanted to meet as long as he could bring Adrienne.

Reiley described Adrienne as a “dynamo” before Alzheimer’s. “She always kept his ego in place,” she said. “She was a gracious, smart and loving person.”

Being the main caregiver

In the New York Times column, Charles wrote that although he had “wonderful helpers” caring for his wife, “real care for a loved one with Alzheimer’s cannot be delegated. I did not need to be told that; I felt it in my bones.”

“The Life Report: Charles Darwin Snelling. A Love Story and Redemption” was the title of the column. “It never occurred to me for a moment that it would not be my duty and my pleasure to take care of my sweetie,” he wrote.

He described his wife in the column as a “very, very sick puppy,” but that she remained “a sweet, happy, loving and generous person.” He wrote that Adrienne had taken care of him “in every possible way she could for 55 years.” Now it was his turn, he wrote, and “certainly I have had the best of the bargain.”

Ed Donley, retired chairman of Air Products and Chemicals and a friend of the Snellings for more than 50 years, said his wife, Inez has Alzheimer’s.

Both men tried to enroll their wives in a clinical trial at Johns Hopkins, where some promising experimental research was being done, he said, but they were told that the women were too old and that the odds of slowing the progression of the disease were low.

Several years ago, Donley and his wife moved to a senior living community that offered care for Alzheimer’s patients. Donley said he encouraged Snelling to consider moving with Adrienne there, but Snelling said he preferred to care for her at their home.

“He felt Adrienne was so devoted to the home where they had lived together, and they had outside help,” Donley said. “He didn’t want to ask her to give it up.”

He said he saw Snelling two or three times at Alzheimer’s support groups but that Snelling, whom he called “a very self-reliant person,” was not a regular attendee.

Marjorie Snelling said that a few years ago, she noticed an exchange between her parents that made her realize “they were clinging to each other for dear life.”

“They would still have a pat on the hand or a moment where you knew they were in­cred­ibly important to each other,” Marjorie said.

On a recent Christmas, Charles and Adrienne sent out cards that showed them walking hand in hand with their backs to the camera, according to a close friend. It said, “going home.”

Staff research director Madonna A. Lebling and staff researcher Magda Jean-Louis contributed to this report.