"I always thought I had been pretty empathetic, and I was ... But I thought I knew how people felt.
"Until you have been through it, you have no idea," he said.
"I now know, losing a loved one is like getting hit in the head with a baseball bat."
Mr Ridley was not sure whether he would be able to continue in his line of work, after the event.
But he knew his son would have wanted him to keep helping others.
"It really changed my perspective - it's a life-changing thing.
"I understand the process they are about to go through, which may take years.
"So you've got to be very careful."
Mr Ridley, however, never assumes to know exactly what someone is feeling and said it is not helpful to say that you do.
This dedication has earned him a Pride of New Zealand nomination, in the Emergency Services category.
"Like many, his life will never be the same and although he continues to have daily personal challenges associated with his loss, he continues to get on with it and give his all to his community," his nominator said.
Mr Ridley, an engineer, joined St John as a volunteer after a former teacher encouraged him.
At first, he was not convinced the role was for him but soon changed his mind and "thoroughly enjoyed it".
He became a fulltime employee 26 years ago.
The area he covers with the helicopter team is the entire lower half of the South Island.
"Sometimes it can be a frustrating job but wonderfully satisfying when you help someone and there's a good outcome for that person."
The Pride of New Zealand Awards are proudly brought to you by The New Zealand Herald, The Hits and TSB Bank.
Nominations for the 2015 awards have now closed.
To see more stories of our wonderful nominees click here.
For more information on the awards go to the official website.