What made United Airlines ground all flights for second time in two months?

United Airline flights have resumed after a network failure exposed just how vulnerable airlines' computer systems often are, says an expert.

Julio Cortez/AP/File
United Airlines jets parked on the tarmac at Newark Liberty International Airport in New Jersey in July 2014. All United Continental flights in the US have resumed after being grounded for more than an hour Wednesday morning.

Passengers are returning to board United Airline flights after being grounded for more than an hour Wednesday morning due to network connectivity problems.

The outage, which had prevented all flights from taking off and forced United’s check-in clerks to hand-write tickets for passengers, began around 8:30 a.m. on the East coast and wasn’t resolved until nearly 10 a.m., according to CNN.

It is the second time in two months that the carrier has experienced major technical issues.

Last month, the airline halted all takeoffs in the US due to what it described as computer automation issues.

The Federal Aviation Administration used the same language in its notice about the outage Wednesday. Officials lifted the block for United flights operated by feeder airlines about 15 minutes after the system crash, but the so-called ground stop for all other flights took considerably longer, reported CNN.

United suffered a series of computer problems in 2012, after switching to a passenger information computer system previously used by its merger partner Continental Airlines. It resulted in the delays of hundreds of flights and lost the company a number of premium business travelers. Later, revenue tumbled.

“We don't know everything behind this morning's issues yet, but today's incident underscores the sense that something is very wrong at United,” Gary Leff, co-founder of the frequent-flier website MilePoint, told the Associated Press.

But Wednesday’s incident exposes yet another example of how sensitive airline computerized systems often are, according to Michael Ibbitson, who leads high-tech operations at London’s Gatwick Airport and spoke to CNN in an interview.

These systems are extremely sensitive and highly complex, and just a single error could misplace the entire system, he told CNN.

But United is far from the only airline that’s been experiencing outages. In March, Jetblue had a similar network failure that grounded passengers on their way to work that Monday morning and lasted about 40 minutes, according to CNN

This report contains material from The Associated Press.

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