What actually failed/broke?
"We like to make sure that we check the equipment all the way down to every connector, every strap we use, the winching machine, everything that is mechanical and we've gone through that, or the engineers have gone through that," he said.
If the "winching machine"
and all its associated kit were good, then one thing that could have gone wrong was him lifting his arms as he got to the door and falling out the strop.
I know from personal experience that the strop gets uncomfortable and I am only 89 kilos, so a larger person would be quite likely in a pretty sore state after being winched and it would almost be a reflex to reach out to the person at the door for assistance, and that would be the last thing the patient should do.