It was a missed message on Microsoft Teams and a voicemail from Telstra’s head of operations that brought the chief executive’s European summer holiday with family to a grinding halt.

Vicki Brady returned to Australia on Friday to face a media firestorm over Telstra’s national mobile outage, and on Saturday it was announced the company would soon face a grilling in the Senate.

At 7am Sydney time on Wednesday, Brady was informed Telstra’s mobile network had suffered a major outage, affecting millions of customers, taking some train services offline, stopping some EV chargers working, preventing shops from being able to use Eftpos, and some customers being able to call triple zero.

Brady’s holiday interruption came two and a half hours after the outage began and after Telstra had publicly confirmed the issue and had alerted the federal government.

Standing before reporters after landing back in Sydney on Friday morning, Brady confirmed the outage was caused by a software fault with Telstra’s time-telling systems.

This defect caused the system to tell the rest of its network that it was November 2006 and led to what one expert said would be a “digital domino chain fall” that brought the network down in minutes in the early hours of Wednesday morning.

Security and authentication measures were thrown into chaos when one part of the network was telling other parts Australia was back in the Howard era, and it resulted in mobile users being kicked off the mobile network.

Telstra subsequently conducted 639 welfare checks on triple-zero users, with seven requiring assistance after initially failing to get through to emergency services.

Brady said she took responsibility to maintain trust in triple zero “extremely seriously”.

“We will complete our investigation into the actions needed to prevent it from happening again. You have my commitment on that,” she said.

As well as apologising to Australians for the outage, the Telstra chief executive had spoken to the family of an elderly woman in South Australia who died during the disruption, a spokesperson said.

Telstra and SA police concluded the outage was not responsible for the woman’s death, but Brady apologised and offered her condolences to family members who were not able to contact each other when their loved one became unwell.

It is the third major national outage in less than a year for the $56bn giant, which powers about 25 million Australian mobile services.

‘Face the music’

Brady has conceded that timing systems were “very well known” and “critical” in mobile networks. Guardian Australia reported on Friday a telco in Jersey suffered a similar outage with an identical time-reset change that had a similar impact on emergency service calls in 2020.

The federal government had also warned the telecommunications sector over the past few years about the critical nature of its time-keeping services on keeping infrastructure operational.

How a known issue could bring down the mobile network used by more Australians from the company that the communications minister, Anika Wells, said held a “special trust” and was “respected as the premium service” will now come into sharp focus.

Executives are set to front a snap meeting of a triple-zero parliamentary inquiry as early as next week.

Federal minister Jason Clare welcomed the scrutiny.

“People could have lost their lives and that’s why there’s an investigation by Acma,” he said on Saturday.

Wells told reporters on Friday that trust “stands in peril” and she would “hold Telstra’s feet to the fire”, saying the telco’s response was not good enough.

“Now that Telstra has resolved its outage, it is time for Telstra to face the music.”

Telstra has 45 days from the time of the outage to provide a report to the Australian Communications and Media Authority (Acma) to explain “very, very clearly why it happened and what the steps that they’ve taken to make sure it won’t happen again,” deputy Acma chair Adam Suckling said on Friday.

Suckling said the investigation would examine the maintenance and configuration of Telstra’s network.

The company could face civil penalties of up to $30m under powers introduced by the government after the 2025 Optus outage.

In May, Telstra sacked more than 100 people and merged two of its largest technology divisions in a restructure, but Brady said the company’s processes “worked as they should have”.

“As the incident occurred, it was identified and then we worked to rectify it as quickly as possible,” she said. “There is no indication that any restructuring of jobs has impacted on this particular issue.

“We will be very transparent and are committed to implementing changes that might be needed.”

Although the new regulatory powers had yet to be tested, RMIT Assoc Prof and telecommunications expert Mark Gregory said Australia’s legislation needed to be rebuilt, “structurally from the ground up and in tune with the modern era”.

“We need to start again,” he said.

The Telecommunications Act, which came into effect in 1997, was written “back when the internet was brand new,” Gregory said.

“Smartphones were not invented, the big tech companies didn’t exist … streaming and all the other things we use these devices for didn’t happen,” he said.

“Connecting railway networks over mobile didn’t happen.”

Wells acknowledged substantial improvements had been made since the Optus 2025 outage but conceded there was more work to be done.

“There is a large gap between the way that this industry has been regulated for a long time – 30 years – to what a modern customer expects of their telco,” she said.

“It is beholden on all of us to address that gap. We’ve been working on it. We’re closing it.

“It is not closed and we all need to do a lot more work to make sure that it closes.”

• Australian Associated Press contributed to this report