From SQ website:

Changes to Flight Schedules on 30 April 2006 (1430-1530 SIN time)
27 April 2006
Please note that there will be slight disruptions to the regular schedule for flights departing and arriving at Singapore Changi Airport between 1430hrs and 1530hrs (SIN time) on 30 April 2006. During this period, approximately 21 flights will be re-timed. This is due to airspace closures resulting from a military exercise that will be conducted on the day.

Customers are advised to check with the Singapore Airlines Customer Service Centre (in Singapore, please telephone +65 6223 8888) for the latest flight information.