“We didn’t have a plan in place for that specific scale of outage. I think it was unexpected,” Kangaratnam told the Senate. “We will take such exercises into consideration in the future.”

Bayer Rosmarin resigned three days after the Senate hearing, and Kangaratnam’s resignation on Friday means both Optus representatives to front the Senate have now departed the company.

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Bayer Rosmarin was the first major casualty of the Senate committee hearings, falling on her sword on November 20, while long-time Optus corporate and public affairs director Sally Oelerich departed in January. Meanwhile, Danielle Keighery in January ditched Optus two weeks before she was set to start as its head of corporate affairs, instead opting to join Qantas.

Optus’ parent company Singtel is still scrambling to find a new CEO and has kicked off a global search to replace Bayer Rosmarin.

Chief financial officer Michael Venter was appointed interim boss on November 20, and potential replacements include former NSW premier Gladys Berejiklian and the head of Optus’ consumer division, Matt Williams.

Singtel is thought to be keen, however, to appoint an external executive to the Optus CEO role, potentially luring someone from overseas, according to a source close to Singtel not authorised to speak publicly.

The Senate inquiry into the Optus outage was originally due to have reported back by February 28, a timeline that was extended this week until May 9. A separate inquiry by the Australian Communications and Media Authority is investigating Optus’ compliance with emergency services obligations.

The telco said the outage was the result of a routine software upgrade from its own parent company, Singtel, which took its network offline and forced staff to physically reboot services. The cause of the outage was first revealed by this masthead.

Analysts have warned that whoever is appointed Optus’ next CEO will need years to rebuild the telco’s reputation. There have also been calls for Singtel to consider selling its Australian subsidiary following two high-profile crises in just over a year.

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Senator Sarah Hanson-Young has said any replacement in Optus’ top job would need to be more communicative with the public.

“Whoever takes it on really needs to restore trust, be a good communicator, and understand that at the end of the day you are offering an essential service,” she said.

“We need a total overhaul of the regulations of these big telecommunications companies … every part of our daily lives is impacted if we can’t use our mobile phone or internet data.”