A computer system failure at the Federal Aviation Authority (FAA) has caused flight cancellations in the US.
The affected system is used to process flight plans.
"We are investigating the cause of the problem," the agency said. "We are processing flight plans manually and expect some delays. We have radar coverage and communications with planes."
A similar system in use in the UK, known as the Flight Data Processing System (FDPS), has had numerous problems and is awaiting replacement.