Optus has pointed the finger at technical equipment for its failure to recognise an emergency call outage as the company's offshore masters blame staff for another.
Singtel chief executive Yuen Kuan Moon and federal Communications Minister Anika Wells met in Sydney on Tuesday following two emergency call outages in a fortnight.
The pair, flanked by under-fire Optus chief executive Stephen Rue and chair John Arthur, discussed technical details about the outages and ways to restore trust in Australia's second-largest telco and the triple-zero system.
Mr Yuen gently backed Mr Rue to lead the telco and said "he is here to provide the solution".
"It's a people issue and it takes time to change and transform the people," Mr Yuen said.
But his comments prompted a scathing retort from the Communication Workers Union, which said the executive's attempt to throw staff under the bus was "utterly outrageous" and "a dirty attempt to shirk responsibility for the telco's systemic failures".
"You don't fix a systemic failure by scapegoating the people on the front line," national secretary Shane Murphy said.
"If the system can't carry a triple-zero call, that's a boardroom failure, not a 'people failure'."
After the Singaporean owners backed Mr Rue, Mr Arthur expressed confidence in the CEO to restore the trust of Australia.
Prime Minister Anthony Albanese had previously said Optus let down its customers and the nation.
The telco has picked consulting firm Kearney to provide "independent expertise".
Optus suffered an outage on September 18 that hit households in SA, WA and the NT and one part of NSW.
That incident, linked to three deaths, is the subject of an Optus probe and a federal communications watchdog investigation.
A separate, localised issue on Sunday barred calls south of Sydney.
Optus apologised to 4500 customers in the NSW south coast town of Dapto after they were unable to make emergency calls for eight hours.
One person needing an ambulance used a phone on another network.
Optus claimed human error caused the first outage after no one diverted calls to a separate part of the core network, as required.
In a statement on Tuesday afternoon, Optus said initial assessments of the second outage indicated 4G services in a tower at Dapto were not operational.
The tower appeared active on the network but calls attaching to it were impacted and did not transfer to other networks, the company said.
Tower equipment from technical partner Ericsson "did not appear to operate as it should".
"Optus' ability to detect the outage was impacted as the Ericsson equipment in the cell tower did not alarm that 4G services were not operational," it said.
Despite the explanations, the communications minister said Singtel was accountable for the telco's failures in making sure calls to emergency services went through.
"That's why I've asked Optus to ... find a way to have an external account in their systems so that Australians can have confidence ... rather than just hearing from Optus again that it will be fine," Ms Wells told reporters in Sydney.
The Greens criticised Ms Wells for appearing to "want to wash her hands of any responsibility".
Senator Sarah Hanson-Young called for conditions to be placed on Optus' licence, including the appointment of an independent expert by the government.
"These big telcos have for far too long put profits ahead of people's safety," the Greens' communications spokeswoman said.
The opposition was equally scathing, arguing the Australian Communications and Media Authority-led inquiry was not sufficient as "they are part of the failed process".
Communications spokeswoman Melissa McIntosh repeated her plea for a wide-ranging triple-zero services review and a public register of outages.
