When the Towers Fall, the Cell Site Learns to Fly

A cell tower’s one great weakness is that it has to stand somewhere. When Hurricane Maria crossed Puerto Rico in September 2017, the Federal Communications Commission reported more than 80 percent of the island’s cell sites out of service, and 22 of its 78 municipalities had lost service entirely. Rebuilding towers takes months. The fastest fix turned out to be putting the radios in the sky while the steel was still on the ground.

The highest fix came from Alphabet’s Project Loon, a fleet of unmanned balloons that ride stratospheric winds. In October 2017 the FCC granted Loon an experimental license to operate over Puerto Rico and the U.S. Virgin Islands, for up to 30 balloons over six months. Each balloon floated some 12 miles up and could cover more than 3,000 square miles, relaying signal from balloon to balloon and down to ordinary LTE phones. The balloons were launched from Nevada and steered across the continent by climbing or sinking into winds blowing the right way, guided by machine learning software. Loon had already shown a balloon could survive 190 days aloft.

Within two weeks of the license, balloons working with AT&T were live over the island, carrying text messages and basic internet access for people with LTE phones. Customers saw the familiar AT&T name at the top of their screens. Most never knew their signal was coming from a balloon.

The lowest fix flew at the opposite end of the sky. AT&T’s disaster teams already had COWs, cells on wheels, truck-mounted towers that drive into a damaged area. In Puerto Rico they debuted the truck’s flying cousin: the Flying COW, short for Cell on Wings, an LTE cell site carried by a drone. It hovered between 200 and 400 feet and covered about 40 square miles around San Juan with voice, data and text service. AT&T said it was the first time an LTE cell site on a drone had been deployed to connect residents after a disaster. The drone flies on a tether, and the tether is the trick: a fiber optic line inside it carries the data and the cable carries power, so unlike a battery drone it can stay up almost indefinitely.

The flying COW became a standing tool rather than a one-off experiment. Improved generations flew over Mexico Beach, Florida, after Hurricane Michael in 2018, and again in the Southeast after Hurricane Ida in 2021, with airframes hardened to keep working in winds up to 50 miles per hour. Verizon and Sprint tested flying cells of their own in the same period.

The logic is the same at 300 feet and at 65,000 feet. Height is coverage: the higher the radio, the more ground it can see, and a radio that flies can be over the damage in days instead of waiting on permits, concrete and steel. The sky is not a permanent place to build a phone network. But when the towers fall, it is where the network goes to survive until they stand again.

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More technology and cellular reading: The Airplane That Is Almost All Wing, the story of the solar aircraft built to do a cell tower’s job from the stratosphere.