Optus' network was set up for failure from the moment it embarked on an upgrade that severed Australians' access to the triple-zero system.
Chief executive Stephen Rue has outlined the causes of the outage on Thursday as the telco's Singapore owner circled the wagons around the embattled Optus boss less than a year into his tenure.
Rue blamed the issue on human error, brushing off concerns parent Singtel had cut spending to Australia's second largest telco.
"Standard processes were not followed," Rue told reporters in Sydney on Wednesday.
"That's not an investment issue, that's people not following process."
"That is a result of human error."
The first step of Optus' firewall upgrade was to divert calls to a separate part of the core network.
But preliminary investigations revealed this had not been followed.
The failure is the second time in two years a major Optus outage has prevented people accessing emergency services.
Pressure has continued to mount on the Optus chief after revelations the company had not implemented a third of the recommendations that followed a review on its 2023 outage.
Rue took the reins in November after the earlier outage and a hacking incident that left millions of customers exposed to potential online fraud that forced the departure of Kelly Bayer Rosmarin as chief executive.
The Opposition and Greens called out federal Communications Minister Anika Wells for flying overseas in the middle of the current crisis, while urging Rue to resign.
Singtel Group defied the demands to sack Rue, a former NBN Co boss brought in to right the ship after scandals.
"Our hearts go out to the families and friends of those who have passed away and we know that Optus will get to the bottom of this matter," Singtel Group chief executive Yuen Kuan Moon said in a statement.
"We will continue to fully support the Optus board and management team as they work through this incident and accelerate the changes needed."
Board chairman John Arthur also appeared to stand by Rue as Optus announced distinguished businesswoman Kerry Schott would lead an independent review on the outage.
"The Optus board is working with CEO Stephen Rue and his team to ensure we develop a full understanding of what went wrong and why, and what we need to do to prevent any repetition," he said in a statement.
Asked about calls for his resignation, Rue said the situation was not about him.
"What we have here is lives have been lost, a failure of triple zero, processes in call centres but also in network, not being followed," he said.
"There are no words that can express how sorry I am about the very sad loss of the lives of four people who could not reach emergency services in their time of need."
Schott's review will press for the causes of the outage and examine the operational management of triple-zero calls on the Optus network.
It will also look at Optus' response to the incident and whether it adhered to policies and legal requirements.
The Federal Court on Wednesday added to the Optus pile-on after approving a AU$100 million (NZ$113.1 million) penalty for the company over "appalling and predatory" conduct in its sales practices.
Optus admitted its sales staff acted unconscionably when selling phones and contracts to more than 400 people at 16 stores nationwide between 2019 and 2023, including vulnerable customers such as Indigenous and intellectually disabled people.
"Senior management abrogated their management responsibilities and, consequently, Optus abrogated any semblance of responsible corporate behaviour," Judge Patrick O'Sullivan said.
Optus' 2023 outage has sparked significant change at rival TPG.
Resilience improvements included real-time network monitoring to detect call-routing anomalies and a welfare check protocol that escalates to police if triple-zero calls fail three times in five minutes, TPG Telecom told AAP.
But it pressed against suggestions the self-regulatory nature of the Australian telco industry had led to repeated failures in emergency call management.
"We don't need more regulation; we need smarter regulation," a spokesman said.
SHARE ME