ARINC has stated that is has restored normal communication service allowing flights to communicate with their operations centers.
The outage happened yesterday (Thursday) and cause delays for U.S. based airlines including United. As a result of the outage, airlines were forced to switch to alternatives.
Until airlines were able to switch to alternative communications, many were forced to use cockpit radios to talk to their network operations centers, NOC, which caused many of the delays.
ARINC had said that an issue with its global messaging processor impacted ACARS for all of its clients and disrupted communications in other industries as well.
ARINC, Aeronautical Radio, is owned by the Carlyle Group based in Annapolis Maryland with communication operations centers in London and Singapore. They provide communications and communication systems for the aviation industry as well as defense and healthcare.