If you told Timmy Palumbo your birth date, three years from now, if he saw you on that day, he'd remember and say, "Today is your birthday. Happy birthday." If he saw your car, he'd memorize the license plate and want to know your mileage. Every day, he checked in with his brother, his grandparents, his aunt, the people he loved, to find out what the weather was like where they were.

His family has many stories like this of Timmy, the funny, energetic, compassionate youngest child of Nick Palumbo. His mother, Sue Sylvester Palumbo, at times can't believe he and her husband are gone. Timmy, 20, died in a plane crash near Ka'au Crater with his father, 81-year-old veterinarian Nick Palumbo, on Sunday. The two were coming home from their regular weekend trip to Läna'i where Dr. Palumbo would treat animals at his no-appointment-necessary clinic and Timmy would serve as greeter.

"With children with special needs, as parents, some might think we would feel better if our child were more conventional, or if he were a high achiever," Palumbo said. "But I would not have traded this kid for anybody."

The official term given to describe Timmy's developmental delays is PDD-NOS (Pervasive Developmental Disorder — not otherwise specified), which is within the autism spectrum.

"Some people say that Tim was disabled but I never bought into that," his older brother, Billy, said in an e-mail. "He was a kid that had different abilities, but he was not any less of a person."

He had what one of his neurologists described as "enthusiasms" about classes of things.

"Timmy loved numbers, mileages, times," Palumbo said. "He would memorize all the complicated instrumentation on his father's plane and could tell if something was a little off."

"Tim was a collector of keys and he knew what each key he had was to," Billy said. "More than that though, you could go through your keychain with him and tell him what each key unlocked once, and months later you could give them to him and he would be able to tell you what each one was for. Also, if you had moved them around your keychain since he last saw them, he would comment on that and be able to tell you what was moved."

He loved the weather and would phone, text and check online every day for the weather where his maternal grandparents live in Tahoe, where Billy is in college at Syracuse, where the family has their house in Läna'i. The bookmarks on his computer say things like, "Billy's weather, Uncle Bill's weather, Lanai weather, Mom's friend's weather."

"My day was never complete without a phone call from Tim asking me 'How's the weather up there?' followed by 'What's the temperature?' " Billy said.

Nick Palumbo had six children from his first marriage and Billy and Timmy with Sue. Of the eight siblings, all had blue eyes except for Timmy, who had twinkling green eyes that matched his wide smile.

"This kid made people laugh," Palumbo said. On Läna'i, he had an old beat-up Jeep Cherokee that he would drive around the Palumbo property. At the top of the driveway sits a statue of Saint Francis of Assisi, patron saint of animals.

"If he was going to drive his Jeep around, he would say, 'Mom, I gotta go say hi to Frank,' " Palumbo said. "That was his little joke."

Like many people affected by autism, Timmy was sensitive to touch. He might tense up a bit in a hug. But on Sunday morning, he let his mom kiss him goodbye as he and his father headed out to the airport. He put his forehead down, pointed to it and said, "OK, Mom" showing her where to put the kiss.

Palumbo would like to establish a scholarship in Timmy's name for the Youth Services Program through Easter Seals. She is on the Easter Seals board. "We definitely want to remember him by doing something like providing services," she said. "Not a plaque on a rock or a building or anything like that, but to help kids with special needs get the services."

Nick and Sue Palumbo, who is also a veterinarian, were married 23 years. "There was a 29-year age difference between us, and so it's pretty natural with that age difference to think that your spouse is going to precede you. But Timmy and I were going to grow old together," Palumbo said.

"Tim was my friend, my weatherman, my encyclopedia of keys, but most of all he was my little brother that I loved with all my heart," Billy said.

Palumbo smiles when she talks about Timmy's enthusiasms, the things that made him laugh, the way he and his father were often arguing but always together.

"My message as the parent of a special-needs child is this: I would not want, nor would Nick, ever, ever want Timmy to have been any different."