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Why did the FAA ground all planes in the US Wednesday morning?

Longtime aviation insiders could not recall an outage of such magnitude caused by a technology breakdown.

WASHINGTON — Thousands of flights were delayed Wednesday morning and hundreds have been canceled as a result of a computer system failure at the Federal Aviation Administration. 

While details are still coming out about the source of the problem, the FAA has said a failure of the NOTAM system overnight caused the world's largest aircraft fleet to be grounded for hours. 

What is NOTAM?

NOTAM stands for Notice to Air Missions, and is an online alert system used by the FAA to warn pilots of dangers along their flight paths. 

The NOTAM system is designed to provide pilots and air traffic controllers with critical information before taking off, like runway hazards or adverse weather conditions. 

John DeCarlo, professor at the University of New Haven and commercial pilot, told WTIC that the NOTAM system affects every part of a flight. 

"It's the news station of the skies," he said. "It literally tells us everything that's happening across the country, locally and far away from where we're taking off."

Before or during a flight, NOTAMs can be issued to pilots warning them of problems such as storms developing over their destination airport. 

Usually, the notices are provided to pilots as part of their pre-flight planning, allowing the pilots to set a flight path that avoids any dangers. 

NOTAM advisories can vary in length, but for some long-haul flights it can be up to several hundred pages. 

What happens when the NOTAM system is down?

Wednesday morning was a showcase of how critical the NOTAM system is to flying in the U.S. Without the system operating correctly, planes have no way of getting critical information on the fly. 

"It's something that we use as part of the flight briefing before we take off," said DeCarlo. "It informs us of any hazards that we have to be concerned with....and things that might affect the safety or operation of a flight."

Because of that risk, the FAA made the call Wednesday to delay all air traffic with a nationwide ground stop until the system could be fixed.

Most nationwide ground stops involve a specific airline, meaning others are able to fly unimpeded. Wednesday's ground stop appeared to be one of the largest since 9/11, affecting all commercial and private planes in the country.

What caused the problem?

It's unclear what happened to make the NOTAM system go entirely offline. White House Press Secretary Karine Jean-Pierre said in a tweet that there was no indication of a cyberattack on the FAA's systems. 

But she said the president had directed the Department of Transportation to conduct a full investigation into what caused the outage. 

President Joe Biden told reporters shortly after that he expected officials would know more about what happened in "a couple of hours."

What about planes already in the air? 

When the FAA decided to ground all flights, planes currently in the air were allowed to continue on their flight paths to their destinations. But those planes didn't have access to the NOTAM system either. 

"You'd be basically flying without a system that was put in place to tell us about outages at air traffic control....cranes in the area, runways, literally everything," DeCarlo said. 

Flights already in the air by the time the ground stop was issued had already received their NOTAM advisories for their flights as part of the pre-takeoff procedure, he said.

Those pilots, however, were still unable to access the online portal that would tell them of any new hazards that had popped up since they started flying. 

Even though the NOTAM system has transitioned to the digital world, the FAA is still able to use older systems for emergencies such as Wednesday's failure. 

"It's a very old system that started as far back as the 1040s," DeCarlo said. "It's modeled after the notice to mariners system (used by ships on the ocean)." 

While the online system was down, pilots relied on a backup system that was mainly used before the internet. They called a hotline operated by the FAA, which provided the latest information on hazards related to their flight. 

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