Ellis has questioned whether Aerocare's training and split shifts had led to fatigue and contributed to the incident.
He said safety checks broke down at several points around the flight - the clipboard being left there in the first place, the failure to notice it on an engineering walkaround and by a staff member on the ramp wearing the headset who dispatches the aircraft.
Aerocare does ground handling for several airlines in New Zealand and says it has one of the best safety records in this region.
A spokesman said both the leading hand and dispatcher said fatigue was not a factor in the event.
Neither had worked split shifts on the day.
"Aerocare is working with New Zealand aviation authorities, and Jetstar, to understand how this one-off incident occurred.
"Aerocare does not force any employee to work a split shift. Unlike other baggage-handling companies, split shifts are at the discretion of employees and not the company. Any suggestion that these workers were therefore fatigued is wrong.''
Aerocare says it has handled more than one million flights in its 25-year history and has never been fined or sanctioned for any safety incident.
Ellis said there could be under-reporting of incidents, which was common in casualised, low-pay work environments.
Aerocare says its staff in New Zealand are all permanent.