WASHINGTON (AP) — Designers of the ambitious U.S. air traffic control system of the future neglected to take drones into account, raising questions about whether it can handle the escalating demand for the unmanned aircraft and predicted congestion in the sky.

“We didn’t understand the magnitude to which (drones) would be an oncoming tidal wave, something that must be dealt with, and quickly,” said Ed Bolton, the Federal Aviation Administration’s assistant administrator for NextGen, as the program is called.