I'm here to review back the Airasia Zero Fare Promotion or Free Seat historical price from 2011 until 2015 as shown in table below. The flight fare sometimes quite cheap but sometimes it's quite expensive depend on the season and peak period like school holiday or public holiday.
In 2009, Airasia started offers ZERO FARE air ticket for all its Asian destinations. Fees are exclusive government tax and airport tax. At that time, the booking period was on November 2009 and travel period was May through October 2010.
The conclusion is
1) AirAsia launches the Free Seat Promotion or Low Fare Promotion more than 3 times per year - currently expected to be in mid-February, early-Jun, mid-August and early November)
2) Travel period is usually 8 to 12 months away
3) Airport taxes, baggage, meals not included - obviously