BOGOTA (Thomson Reuters Foundation) - Aeromexico and the Mexican government are teaming up to train airline staff and crew to spot possible victims of human trafficking, a global crime fueled by “lack of visibility, indifference and tolerance,” officials said.

Workers at Mexico’s largest air carrier will be trained to detect and report signs of trafficking by Mexico’s National Human Rights Commission (CNDH), Aeromexico said in a statement.

An estimated 40 million people around the world live in slavery, which includes human trafficking. Illegal profits are thought to be about $150 billion a year.

“It feeds off a lack of visibility, indifference and tolerance of practices that have become socially normalized,” Aeromexico and the CNDH said in a joint statement on Monday.

The training addresses various forms of trafficking, from sex work to labor exploitation and forced marriage, and sets out a protocol for airline staff and crew to follow if they see possible victims.

Aeromexico operates more than 600 flights per day, and its hub is in Mexico City. The company serves more than 90 cities in Mexico, the United States, Latin America, Canada, Europe and Asia.

Planes are a key part of the illegal business, as criminal gangs transport thousands of forced laborers each year.

Potential victims of trafficking may be young women, men or children who are frightened, nervous or appear under the control of others, experts say.

Other signs of trafficking are passengers flying on tickets with multiple stop overs, a cheap way to travel, and have visas and work contracts in a foreign language, experts say.

In Mexico and across Latin America, the most common form of human trafficking involves women and girls forced into sex work.

Nearly 380,000 people are trapped in modern slavery in Mexico, according to the 2016 Global Slavery Index by rights group Walk Free Foundation.