The technician who led the working shift at the Ho Chi Minh City Area Control Center (ACC) when the power went out and affected nearly 100 flights last month was Friday put in police custody for investigation, a source close to the matter said the same day.

Le Tri Tinh, the shift leader directly involved in an unprecedented incident in Vietnamese aviation history, was arrested at home and had his workplace searched by Ho Chi Minh City investigative police around 10:00 am, according to the source from the Vietnam Air Traffic Management Corporation (VATM).

The ACC, operated by the Southern Airports Corporation, a VATM subsidiary, oversees flights to and from Tan Son Nhat International Airport – Vietnam’s largest terminal, which handles about 20 million passengers a year.

Ninety-two flights, including 54 within the city’s flight information region at the time of the outage, were affected when the power at the ACC cut out on November 20.

The VATM initially attributed the power loss to human error, specifically the team working at the center at the time of the incident.

The ACC has three sources of electricity, the national grid, three generators and three uninterruptible power supply (UPS) systems.

At 11:00 am on November 20, the power supply system at the ACC underwent a regular check by technicians from the Southern Airports Corporation, VATM general director Dinh Viet Thang told a media meeting on November 24.

Power from the national grid was disconnected, and the ACC was then powered by the three generators.

At 11:05 am, one of the UPS’s broke down.

“Under the proper procedure, the failed UPS must be isolated from the power supply system, but the shift leader, Le Tri Tinh, turned it off before doing so, which led to the failure of the other two UPS’s,” Thang said.

After the power was cut, instead of reconnecting the system (which had been turned off for the check) with the national grid to power the air traffic control system, the technicians focused on repairing the UPS’s.

The ACC’s power system was only reconnected to the national grid 14 minutes after the incident occurred, Thang said.

But Tinh made another mistake with the UPS, which disrupted electricity for the air traffic control system again.

“The power issues were only fixed at 11:36 am, and the ACC resumed operations at 11:40 am,” Thang said.

Tinh and the technician working with him during the shift were suspended from duty immediately after the incident for investigation.

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