It’s part of the FAA’s ongoing $20 billion overhaul of U.S. airspace aims to boost safety and efficiency in increasingly busy air corridors across the U.S. But business jet operators are quickly running of runway ahead of an FAA-mandated deadline to equip all aircraft with ADS-B before Jan. 1, 2020.

While passenger airlines have moved to upgrade their jetliners on time, operators of business jets have proved particularly slow to bring their aircraft up to spec. Government research shop MITRE estimates that out of 26,700 business jets in the U.S., 20,731 still needed to be equipped as of March 2017. “The industry should be doing double what it’s doing now, per day,” says Mark Francetic, regional avionics sales manager for Duncan Aviation, one of the handful of companies equipped to perform ADS-B installs. “Right now if we continue on our path, we’re looking at meeting about 50 percent of airplanes.”

Related: You No Longer Have to Register Your Drone

That estimate could prove optimistic. While hard data on installs is scarce, industry sources estimate that avionics shops nationwide average anywhere from 75 to 160 installs per month. Even at the high end, that would leave some 15,000 aircraft grounded on the first day of 2020. And even if business fliers rushed to add the technology closer to the deadline, they’re likely to run into delays, since the number of aviation shops that can install it are limited.

Grounding thousands of aircraft could temporarily bring the business aviation industry—which employs 1.2 million people and contributes $150 billion to U.S. economic output—to a screeching halt, but there’s little chance the FAA will extend the deadline, industry sources say.

“When we have ADS-B for everyone, that’s when we actually get return on this investment,” says Chris Benich, head of regulatory affairs at Honeywell (HON), a maker of ADS-B components. “That’s why they’re going to stick with that date. That date isn’t moving.”

A version of this article appears in the Aug. 1, 2017 issue of Fortune.