Human factors are the things that go wrong in the interactions between a team of people and a system of technology. This is part of a broader transdisciplinary field called engineering psychology, which as the name suggests, draws from both engineering and psychology. Many, if not most, catastrophic accidents involve a socio-technical interaction, i.e. are not solely due to technology failure. Hence, there is a need to consider human factors in the development or deployment of any technical system. This article is about the human factors involved in an aviation accident in New Zealand between a Yak and a cherry picker. The types of human error are identified, and the barrier bowtie method is used to represent them. The analysis gives different insights into the accident compared to the formal accident report, and better represents the human error characteristics.