Vicki Brady has detailed what led up to the March 1 outage, saying the issues started at 3.30am when callers’ locations and phone numbers – or “calling line identification” – was not coming up on calls.

Telstra needed those details to transfer callers to emergency services, and so had to switch to its backup process whereby operators manually asked callers where they were located before passing them onto the correct emergency service.

Telstra managed to successfully make 346 calls through this process.

However, another 127 callers languished in wait because the telco had incorrect emergency service numbers on file.

Telstra had 24 back-up phone numbers for state emergency services on file and eight of them were wrong, Ms Brady revealed.

That meant the 127 callers had to wait for an email transfer and call back, while another 21 callers said they no longer required emergency assistance.

The failures did not end there, though, with Ms Brady noting further delays in call backs because a staff member incorrectly typed in an email address.

“When our team identified an issue with the phone numbers they resorted to email, and were supplied an updated email address for Triple Zero Victoria during the incident,” the Telstra boss said in a blog post on Wednesday.

“This address was incorrectly entered into the system. Our team identified the error within 13 minutes, but this did still cause a delay.

“Ensuring we have the right contact numbers for emergency services operators is basic and something we should have gotten right.”

Ms Brady was personally overseeing Telstra’s work to avoid further failures, including updating instructions to staff to diagnose and address any future issues quicker.

Within 90 minutes of the incident starting on March 1, the service returned to normal, she said.

“As CEO of Telstra, I apologise to everyone who tried to call Triple Zero during this issue, and in particular, the family of a man who suffered a cardiac arrest and tragically passed away,” Ms Brady said.