The Oireachtas Banking inquiry resumed after lunch with AIB chief executive David Duffy answering questions.
Mr Duffy, who is leaving the institution, said the scale of the crisis has been “staggering”.
Mr Duffy said 4,000 people have left the bank since he took over and there has been a cut of €350 million in operating costs.
He said this was “exceptional and staggering in terms of the scale” at the one institution.
Mr Duffy, who has been chief executive since 2011, said there was disarray at the bank when he arrived because there had been “too many” changes at senior level.
The chief executive said there was “uncertainty” because of the change in the leadership and a fear among staff about individual roles.
He said there needed to be a culture change to an external lens rather than an internal focus.
Asked by Senator Michael D’Arcy if the job was done, Mr Duffy said: “I don’t believe it is complete and finished work.”
He said there was a “deeply embedded culture of the lifestyle and livelihood of working in a bank” that needed to be shifted to a customer focus.
Mr Duffy confirmed there was a herd mentality in banks across the world and that was no different in Ireland.
Mr Duffy said the National Assets Management Agency has proven to be extremely helpful to us.
He said the use of consultants has been limited since he took over as chief executive in 2011.
Mr Duffy said a guarantee “of some kind” had to be applied or there would have been a more “dramatic and severe outcome”.
He said letting one or two banks fall “would have created a risk to this country” but it is “impossible to predict” the consequences.
The chief executive said the train was travelling at 200 miles an hour in the wrong direction when he arrived at the bank.
Mr Duffy said he did not spend too much time considering the past but instead focusing on the future,
In his written statement, Mr Duffy said a major overhaul of AIB was needed when he took over.
He said: "Clearly upon my arrival at the bank there were concerns about the banks' culture and governance. There was a need to rebuild trust between the bank, the taxpayers and its key stakeholders including the Department of Finance and the Central Bank.
“Deficiencies had been identified within the Group’s Risk Framework and the bank had a significant number of internally and externally imposed issues to work through as part of a Risk Mitigation Programme.
“The customer model was highly challenged after a significant period of inward focus and there was limited organisational ability to help people in financial distress.”
Earlier today at the inquiry, Eugene Sheehy and Michael Buckley, former chief executives of AIB, both apologised for their roles in the banking crisis.
