Communications Minister Malcolm Turnbull has commissioned a fifth audit of the national broadband network since coming to office in September.

The inquiry will concentrate on the period from April 2008 to May 2010. It will look into the processes that led to the creation of NBN Co, the builder of the network, and the steps leading to an implementation study. It is in addition to a review of NBN Co governance already under way by advisory firm KordaMentha.

Communications Minister Malcolm Turnbul. Credit:Rob Homer

Mr Turnbull has appointed former Telstra director Bill Scales to head the audit. A statement from Mr Turnbull's office said Mr Scales brought "a wealth of experience in public policy and telecommunications to the role". He has been chairman of the Industry Commission (now the Productivity Commission), secretary of Victoria’s Department of Premier and Cabinet and has been involved with other high-profile inquiries including the Gonski Review.

In an interview published on the Australian Institute of Company Directors website last year, Mr Scales said he had spent five years as Dr Ziggy Switkowski's chief of staff while at Telstra. A former Telstra CEO, Dr Switkowski is now executive chairman of NBN Co.