An aviation source familiar with what controllers are dealing with has told CNN that the outages behind the US ground stop involve air traffic control radars and radio frequencies going out at the same time, and that controllers have no clarity on the cause.
This is a second, independent account that radar is affected as well as radio communications. The first came earlier on Friday from an internal Alaska Airlines message seen by CNBC.
Separately, MPR News reports that the FAA has reported frequency and radar outages between several air traffic control centres. That attribution to the FAA is MPR's alone. The FAA's spokesperson has so far said only that there is a communications problem affecting Air Route Traffic Control Centers, and no FAA statement we have seen mentions radar.
The CNN source's account is unofficial and has not been independently checked. Neither the FAA nor Transportation Secretary Sean Duffy has confirmed radar failures, and neither has said what caused the outages or whether a cyber attack is suspected.