Why a 15-year-old girl's beautiful act of kindness is going viral.

When a blind and deaf man named Tim boarded a six-hour cross-country flight from Boston to Los Angeles, no one was able to communicate with him – until a 15-year-old girl grabbed his hands.

Clara Daly, who has been studying sign language for the last year, came to Tim’s aid when flight attendants put a call-out over the plane’s speakers, asking whether any passengers knew sign language.

According to a viral Facebook post shared by fellow passenger Lynette Scribner, Clara communicated with the man by signing letters with her fingers which he read by holding them.

“It was fascinating to watch as she signed one letter at a time into his hand. He was able to ‘read’ her signing and they carried on an animated conversation,” Lynette wrote.

While Clara was on the Alaska Airlines flight with her mother, Tim was travelling alone, heading home to Portland after visiting his sister in Boston.

Speaking to CNN, Clara said she helped Tim three times throughout the flight, “once to get him water, another to tell him the time and the last hour of the flight just to talk to him.”

In the last hour of the flight, the pair spoke about their families, Tim’s past career and Clara’s plans for the future.

In the Facebook post, which has now been shared over 500,000 times, Lynette described how heartwarming the encounter was.

“I don’t know when I’ve ever seen so many people rally to take care of another human being,” she wrote.

“All of us in the immediate rows were laughing and smiling and enjoying his obvious delight in having someone to talk to.”

“I can’t say enough about this beautiful young woman named Clara who didn’t think twice about helping her fellow passenger. It was a beautiful reminder, in this time of too much awfulness, that there are still good, good people who are willing to look out for each other,” she added.

According to the post, Alaskan Airlines have reached out to Clara, Tim, and all those involved.

“Clara was amazing,” an Alaskan Airlines flight attendant said.

“You could tell Tim was very excited to have someone he could speak to and she was such an angel.”