An Air New Zealand plane that had dropped off international returnees to enter managed isolation then carried domestic passengers without a deep clean in between.
In a statement, the company confirmed that "a number" of months ago an aircraft that had operated an MIQ charter service was inadvertently scheduled to continue operating instead of returning to Auckland to be cleaned.
The company would not confirm when the flight occurred or where it landed, but Managed Isolation facilities are in Christchurch, Wellington, Hamilton and Rotorua.
An Air New Zealand staff member told the Herald the flight may have been either late last year or early this year.
Air New Zealand also would not confirm whether those flying on the second trip were later informed of the mishap.
General manager cabin crew Leeanne Langridge said after this event they reviewed their processes to prevent a recurrence, which included checking that MIQ charter flights were appropriately flagged in their system.
"And that the specific type of cleaning required immediately after flights of this nature has been scheduled. We continue to review our processes on an ongoing basis to make sure our customers and our people are kept safe," Langridge said.
"Crew members are encouraged to report any event through our safety reporting system – there have been no reports of a similar nature since."
There have been no cases of customers or aircrew contracting Covid-19 from aircraft surfaces while travelling on subsequent domestic flights following MIQ charters.
Those on board MIQ charter services are required to wear a mask for the duration of the flight to prevent droplets being spread through the air or onto aircraft surfaces.
A Ministry of Health spokesperson said the ministry was aware of the incident and that the company had since tightened its cleaning processes.
Epidemiologist Michael Baker said the main way you can get the virus is by being in an indoor environment with others that are infected.
"There's no evidence of anyone getting the infection from an un-cleaned aircraft, or even any surface, I know there's this huge focus on deep cleaning everything after anyone who might have been infected has used that environment, but it may have been overemphasised."
He didn't think, given the level of risk, the people on the second flight should have been informed of the plane's prior MIQ trip.