insider & Epiphany, I appreciate the pre-takeoff checklists are important. We have no evidence yet whether the pilot used a pre-takeoff checklist. Even if he did, some intervening event could have disturbed his flow. I once flew with an experienced instructor who went through his entire Raven II checklist, expect he'd forgotten the very first item - secure seatbelt ! Imagine his embarrassment when another pilot in a Cessna nearby kept pointing to the buckle hanging out side his door.
I think pilots are not trained enough on the "what if" sceanarios and they haven't a clue what to do if something unexpected crops up. As Tarman pointed out, he could have just switched it back on whilst in the hover.