Vietnam Airlines workers at Tan Son Nhat Airport in Ho Chi Minh City had to manually handle procedures for hundreds of passengers for over a hour after a rainstorm caused a power loss and affected the check-in systems yesterday.  The power outage occurred at about 1:10 pm Sunday during a thunderstorm that interrupted the computerized check-in systems at both the domestic and international terminals of the airport.   The airport immediately began using its standby power source, but the check-in system did not come back online, national carrier spokesperson Le Truong Giang told Tuoi Tre. As a result, airline employees had to carry out check-in by hand, leading to delays for 12 flights, both local and international, impacting more than 1,000 passengers, Giang said. The check-in system was not repaired until 2:50 pm, while the storm, along with violent winds, continued sweeping through the city, knocking down many trees, tearing roofs of houses and leaving several buildings collapsed. A similar situation occurred at the airport in April 2011, when a powerful storm caused a power outage at the domestic terminal.