Mexico’s new president shut down construction of a massive airport intended to service Mexico City, but the plan to use three separate, smaller airports in its place will be “very, very, very challenging,” according to the head of the International Air Transport Association (IATA).

Bloomberg reports that IATA CEO Alexandre de Juniac expressed both operational and safety concerns in remarks at an industry conference held in Mexico City.

President Andres Manuel Lopez Obrador fulfilled a campaign promise to halt the $13-billion international airport project, and Mexican aviation officials said that instead the city’s existing airport and another in Toluca would be upgraded. A military airport also would be converted to commercial use under the plan.

The new airport was about one-third completed when it was shut down. The existing Mexico City International Airport is straining to meet demand and cannot be expanded.

Airline officials said the three replacement airports are too far apart and that their operational requirements favor flying out of a single airport, not having aircraft scattered over multiple hubs. The CEO of Mexican low-cost carrier Volaris, which was founded at the Toluca airport, said the airline left because the market there didn’t support its operations.

“Airlines urgently need to know what infrastructure will be available and when,” de Juniac said. “And if the decision is politically motivated, the results will be sub-optimal.”