The mid-band 5G spectrum known as C-band, which US operators shelled out billions for at the start of this year, has encountered an unexpected obstacle.

According to a report in the WSJ, US operators AT&T and Verizon are delaying their planned rollout of services across the 3.7-4.2 GHz band because comms regulator FCC and aviation regulator FAA are worried they may interfere with airplane cockpit safety systems. Presumably they also use that frequency.

“Aviation safety and technology leadership are national priorities, and with today’s announcement these companies have demonstrated their commitment to both,” said the agencies in a joint statement to the WSJ. Neither of them have seen fit to make any formal announcements on their websites, however, suggesting a desire to keep the matter as quiet as possible. The development is also conspicuous by its absence on the operator press sites.

C-band 5G services were due to commence on 5 December and they have now been delayed for a month. As the report notes, that alone is not a big deal for companies taking years to ramp up their 5G offering. But the unexpectedness of the announcement and the prospect of further delays if the concerns are not resolved in the extra month on offer create the potential for a more profound crisis.

To the best of our knowledge the prospect of aviation interference was not discussed when US operators dropped $81 billion on this spectrum at the start of the year. That it should then require a delay, no matter how short, when all concerned have had a further ten months to explore the matter is baffling. This seems to be an FAA thing, so it’s incumbent on that agency to either substantiate its concerns with hard evidence or back off.