The policy on career breaks 3 years ago was that they are available but I doubt in the form most are familiar with - if you wanted to take one you effectively resigned from the company. After 3 years you can apply through the normal recruitment process and should you be successful you would be re-employed on the new entrant contact in force at the time with a new seniority number, new date of joining and a seat on whichever fleet has vacancies.
That said I'm sure in 2008 6-12 month career breaks were offered due to the GFC but were subject to a very short recall period.