Last year, I made the most personal film of my career, about my father Eli’s death. In January 2021, aged 92, Dad was in hospital, bedbound, with no prospect of recovery. My mother was struggling to cope. The only option appeared to be going to a facility for his remaining months.I’ve been a film-maker for 30 years and have always dreamed of telling my father’s story. I tend to make films about characters I describe as “impossible visionaries”: people with a singular vision who sometimes act impossibly to try and realise it – and to withstand the doubt and ridicule they incur.Sometimes, that’s just a nice way to describe a megalomaniac, but I’m attracted to telling the stories of people who push the boundaries, because I think – rightly or wrongly – they will inspire others to live more interesting, gut-driven lives.In my film, Dig! we see Anton Newcombe lead the band the Brian Jonestown Massacre through countless brilliant records while simultaneously sabotaging every opportunity at commercial success. For We Live in Public, I followed Josh Harris as he spent his dot.com millions creating a live-in social experiment inside a Manhattan-based cyber bunker to try and prove the loss of intimacy and privacy that would come with broadband internet.I watched Russell Brand search for a higher purpose in Brand: A Second Coming, while Matt Smith took the lead in my biopic of Robert Mapplethorpe, the controversial photographer best known for his S&M shots and salacious flowers.My original visionary … the Timoner family (with a young Ondi second from right) in October 1979 pose with one of Eli’s Air Florida jets. Photograph: Courtesy of MTV Documentary FilmDad was my original impossible visionary: the most tenacious and innovative person I’ve ever known. Fifty years ago, he founded an airline, Air Florida, which became the fastest-growing airline in the world. One day 10 years later, aged 53, he ran six miles and led a meeting of 1,000 employees, before going in for a massage, during which he received a rudimentary “neck crack” to relieve stress. The procedure damaged an artery, which swelled instantly, resulting in a debilitating stroke that left Dad paralysed on one side of his body and blind in his left eye.He was ousted from the airline and lost everything financially. Yet his humour, resilience and grace allowed him to continue to live a rich and successful life for the next 40 years.The prospect of being separated from his family at the start of last year was, however, unthinkable to him. After living with paralysis for so many years and never complaining, Dad was desperately asking for help. We needed to honour his wishes, but how?Some years ago, I was very moved by a film I saw by Peter Richardson called How to Die in Oregon. It followed several people who legally took their own lives when that state became the first in the US to allow it. I never will forget the final shots, from outside the draped windows, as the main character said her final goodbyes and took the drink that would kill her. That was 2011.Ten years later, as my father was suddenly pleading for us to help him end his life, I had no idea that it had become a right in California. My brother discovered a law allowing terminally ill patients to end their lives after a 15-day waiting period. We brought him home to begin hospice care – and started the clock. We installed his hospital bed in the middle of the living room and put out word to friends and family he would be leaving us on 3 March, the date of his choosing.Film-making was there for me like an old friend … Ondi Timoner. Photograph: Joe Maher/Getty Images for BFII felt an unstoppable urge to film Dad, but I was worried. Was I trying to use the cameras to distance myself from the fact that my father was dying? Or would it disrupt the experience of my family? I saw a therapist who said I should follow my instincts – and, most importantly, my father agreed.Film-making was there for me like an old friend. It allowed me to be fully present as my father’s daughter and the quarterback of his care, because I didn’t have to worry about forgetting the sound of his voice or the precious and often hilarious things he said.Three weeks after he died, we held an online memorial service. My sister asked me to make a five-minute video for it. I hadn’t wanted to touch the footage so early in my grief, but when I did, I was stunned. My father was alive within my editing system, but he was also no longer suffering. He had the right to die on his terms, and I was able to grieve with him, laughing and crying for hours on end, revisiting that sacred space through the objective eyes of the camera. I had a new appreciation for the infinite and magical power of film.A week later, I delivered a 32-minute video for the memorial service. From there, I couldn’t stop editing. As I went from daughter to film-maker, I noticed that everyone coming into my parents’ living room left it changed. They seemed comforted and buoyed by my father’s fearlessness, love – and sharp wit. Watching this – noticing it now, despite having been in the room while it happened – was the most transformative experience of my life.I think one of the miracles of cinema is that the more intimate the film-maker goes, the more relatable and affecting our work can be. I invite audiences into my parents’ home without mediation or narration, which frees them to have their own personal interaction with the world in front of them – and people tell me they see their own families on screen, even as they get to know my own.My mother watched any version I cut of the film every day for the first year after my father died. She wanted to spend time with him. Now she tours the world with the film, to share her husband with others. I think a key reason my father was determined to end his life was because he felt he could do more to help us if he was free from his body. Now, he lives in the hearts and minds, not just of his family, but of strangers too, as a beautiful vision of humanity teaching us as much about how to live as how we might die. Last Flight Home is released on 25 November in cinemas.