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Air traffic system failure caused by computer memory shortage.

By Alwyn Scott and Joseph Menn

A common design problem in the USairtrafficcontrolsystemmade it possible for a U-2 spy plane to spark acomputerglitch that recently grounded or delayed hundreds of Los Angeles area flights, according to an inside account and security experts.

In theory, the same vulnerability could have been used by an attacker in a deliberate shut-down, the experts said, though two people familiar with the incident said it would be difficult to replicate the exact conditions.

The error blanked out a broad swath of the southwesternUnited States, from theWest Coasttowestern Arizonnd fromsouthern Nevadato theMexicoborder.

As aircraft flew through the region, the $2.4 billionsystemmade by Lockheed Martin Corp, cycled off and on trying to fix the error, triggered by a lack of altitude information in the U-2′s flight plan, according to the sources, who were not authorized to speak publicly about the incident.

No accidents or injuries were reported from the April 30failure, though numerous flights were delayed or canceled.

Lockheed Martin said it conducts "robust testing" on all its systems and referred further questions about the En Route Automation Modernization (ERAM)systemto the Federal Aviation Administration.

F spokeswomanLaura Brownsaid thecomputerhad to examine a large number ofairroutes to "de-conflict the aircraft with lower-altitude flights".

She said that process "used a large amount of availablememoryand interrupted thecomputer's other flight-processing functions".

The F later set thesystemto require altitudes for every flight plan and addedmemoryto thesystem, which should prevent such problems in the future, Brown said.


When thesystemwent out,airtrafficcontrollers working in the regional center switched to a back-upsystemso they could see the planes on their screens, according to one of the sources.

Paper slips and telephones were used to relay information about planes to other control centers.

The ERAMsystemfailed because it limits how much data each plane can send it, according to the sources. Most planes have simple flight plans, so they do not exceed that limit.

But a U-2 operating at high altitude that day had a complex flight plan that put it close to thesystem's limit, the sources said.

The plan showed the plane going in and out of the Los Angeles control area multiple times, not a simple point-to-point route like most flights, they said.

The flight plan did not contain an altitude for the flight, one of the sources said. While a controller entered the usual altitude for a U-2 plane -- about 18,300 metres -- thesystembegan to consider all altitudes between ground level and infinity.

The conflict generated error messages andcausedthesystemto begin cycling through restarts.

"Thesystemis only designed to take so much data per airplane," one of the sources said. "It keeps failing itself because it's exceeded the limit of what it can do."


The sources said the circumstances would be difficult for an attacker to mimic, since they involved a complex flight plan, an altitude discrepancy and an input from the controller that added to the flight plan data.

Former military and commercial pilots said flight plans are generally carefully checked and manually entered into theairtrafficcontrol computers, which are owned by the F.

"It would be hard to replicate by a hostile government, but it shows a very basic limitation of thesystem," said a former military and commercial pilot.

Cyber-attacks on aviation have been an area of increased concern for intelligence officials, who said earlier this year they will set up a new center inMarylandfor sharing information on detected and possible threats.

Security experts said that from the description by insiders, thefailureappeared to have been made possible by the sort of routine programming mistake that should have been identified in testing before it was deployed.

"That's when you put in values anywhere that a human could put in a number, like minus one feet, or a million feet, to see what that would do," saidJeff Moss, founder of theBlack Hatand Def Con security conferences and an advisor to theDepartment of Homeland Security.

While it might be logical to limit the amount of data associated with one flight plan, anything exceeding that amount should not be able to render thesystemuseless, they said.

Though they welcomed the F's assurance that a fix was being rolled out, they said the incident suggested that similar failures could be found.

"If it's now understood that there are flight plans that cause the automatedsystemto fail, then the flight plan is an 'attack surface,'" saidDan Kaminsky, co-founder of the White Ops security firm and an expert in attacks based on over-filling areas ofcomputermemory.

"It's certainly possible that there are other forms of flight plans that could cause similar or even worse effects," Kaminsky said. "This is part of the downside of automation."

Moss said many hackers have been studying aspects of a new $40 billionairtrafficcontrolsystem, known as NextGen, which encompasses ERAM, including its reliance on Global PositioningSystemdata that could be faked.

At least two talks at this summer's Def Con will look at potential weaknesses in thesystem.

"It's very over-budget and behind schedule, so it doesn't surprise me that it's got some bugs -- it's the way it presented itself" that's alarming, Moss said.

Butairtrafficcontrollers and pilots said ERAM is a vast improvement over past systems and that it is needed to fit growing planetrafficinto the airspace safely.

Nate Pair, president of theLos Angeles Centerfor theNationalAirTrafficControllers Association, said it was remarkable that ERAM was restored less than an hour after the outage, limiting the effect on travelers.

"We were completely shut down and 46 minutes later we were back up and running," Pair said.

"That could have easily been several hours and then we would have been into flight delays for days because of the ripple effects."

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Publication:Cyprus Mail (Cyprus)
Date:May 12, 2014
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