Trains linking the main and satellite terminals at Suvarnabhumi airport were out of service for more than two and a half hours on Friday during a check on the electrical system.

The rail system taking travellers to SAT-1 stopped at 9.45am after power was shut off for regular maintenance. The reserve power system did not supply electricity to the trains, said the Airports of Thailand (AoT) president.

Normal service resumed at 1pm. During the outage, four flights were delayed for about 30 minutes each but no passengers were stranded, he said.

SAT-1 handled three arriving and seven departing flights involving 2,422 travellers during the period. The airport used shuttle buses operated by Thai Airways International to transport passengers in the absence of the train service.

The new underground train system, officially called the Automated Power Mover, runs at a maximum speed of 80 kilometres per hour and can carry about 6,000 passengers per hour. Each trip between the two terminals takes three minutes.

SAT-1 opened its doors on Sept 28 and has 28 gates that can  handle up to 15 million passengers a year, allowing Suvarnabhumi to increase its annual capacity to 60 million from 45 million.