The operator of the Tiger Sky Tower at Sentosa must appoint a specialist professional engineer in amusement ride engineering to investigate the cause of an incident on Saturday that left 39 people stranded for four hours, the Building and Construction Authority (BCA) said yesterday.

An investigation report must be submitted before the end of the month. The operator must carry out the repairs recommended by the engineer. After the repairs, the engineer must conduct functional tests and submit another report by the middle of September, before getting BCA's written consent for the ride to resume operations.

The tower is closed until further notice. The cause of the mechanical fault that resulted in the tower's third breakdown in seven years is still being investigated.

Those stranded were rescued at 9.45pm, more than four hours after the fault was first reported at 5.35pm.

The Singapore Civil Defence Force's elite Disaster Assistance and Rescue Team climbed to the top of the tower before rappelling down and into the gondola - with a team on standby to rescue the passengers from height.

The gondola was eventually lowered and the passengers emerged unhurt. Those trapped included tourists from Vietnam and four children.

Sky Tower director Alexander Melchers previously told The Straits Times that the gondola was never at risk of plunging completely as the ride has fail-safes similar to those in elevators.

Lydia Lam