The U.S. airline industry suffers about one technology outage per month, most of them serious enough to disrupt flights.
However, regulators don't oversee airline information-technology systems, and outages aren't covered by consumer protections for passengers.
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The Government Accountability Office reported Wednesday that it counted 34 outages from 2015 through 2017, and 85% caused delays or cancellations.
GAO says airline systems are complicated because they developed over many years and different ones were combined after a wave of mergers.
The government doesn't track outages, so researchers had to use other sources, and they don't know how many passengers were affected.
A 2018 outage at a regional subsidiary cost American Airlines 3,000 flights and $35 million in pretax income. A three-day outage in 2016 cost Delta $150 million in lost revenue.