The 61-year-old father of David, 24, and Kathryn, 18, slammed into the side of a turning vehicle on Meiklejohn Way, his bike tumbling on to the asphalt just after 10am.
A neighbour heard a "big bang" and screaming, and sat with Heilbronn until an ambulance arrived. He could not be saved.
"I was just praying he was alive but I wasn't sure," she said.
The car's 52-year-old driver and her teen passenger escaped injury.
David Heilbronn said police told the family his father was travelling straight when the oncoming car turned into his path.
"He slammed into the side of her ... Maybe he was coming back from the bach. He really loved swimming there, he loved to surf. It looks like he was just enjoying the place."
Chris Heilbronn's tearful widow, Jeanette, said: "It was just an awful, awful accident."
Her husband was "capable and resilient", in roles that included a partnership at Deloitte, CEO of New Zealand Land and Kensington Swan, and planning and strategy GM at the Auckland District Health Board since migrating from the UK more than 30 years ago.
No matter how high he rose, he took his co-workers with him, Jeanette Heilbronn said.
"He always had a way of putting things that pointed out what needed to be done without making anyone feel small. I don't think there's anybody who disliked him."
BDO chairman David O'Connor said staff closest to Heilbronn, especially the young for whom he was a mentor, were devastated.
David Heilbronn said his father had been riding motorcycles since he was 16, a joy he passed on to his son. It had been his father's dream to own a Ducati, which he bought five years ago.
"It wasn't the fastest you get because he ... wanted something that was fun to drive and not dangerous," David Heilbronn said.
"He and the slowpokes would sit at the back and enjoy a cuppa and tootle back at their own pace.
"That's something my dad taught me, driving safely. He used to say, 'Heads and hubcaps - you see the hubcaps moving and you don't see the head looking at you. You've got to wait, or honk your horn or just be careful'."