American Airlines, United and Delta are grounding flights citing communications issues, according to the Federal Aviation Administration’s advisory page — as mass IT outages affect businesses across the world. The groundings come hours after Microsoft said it had resolved a cloud services outage that had forced a grounding of Frontier and Sun Country flights, though it is unclear if the groundings of departing flights from major air carriers are related. Cybersecurity firm CrowdStrike, in a recorded phone message, said it was aware of reports of Microsoft Windows errors related to its technology.