SpiceJet airlines on Tuesday announced it is offering one-way fares starting at Rs 511 (excluding taxes) over a two-day sale offer to celebrate its 11th anniversary. Fares on foreign routes (excluding taxes) begin at Rs 2,111.The discounted tickets can be booked Tuesday through Thursday and are valid for travel from June 15 to September 30 (domestic bookings) and June 1 to July 20 (international bookings). SpiceJet said limited number of discounted tickets are available on a first-come, first-serve basis. The June-September quarter is traditionally a lean season for travel as schools and colleges reopen after summer break. Discounts help push sales and increase load factors. In fact, SpiceJet has been consistently reporting 90%-plus load factors for the past 11 months.