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Pressure vests were choking F-22 pilots

After years of investigation, the U.S. Air Force has figured out "with high confidence" the "mosaic" of factors that have been almost literally choking the pilots of its premiere fighter jet, the  F-22 Raptor, service officials announced today.

The heart of the problem is an oxygen valve on the early 1990s-vintage pressure vest worn by Raptor pilots. This valve was inflating the vest from the moment the pilots took off, making it hard for them to breathe and leading F-22 pilots to report hypoxia-like symptoms, according to Maj. Gen. Charles Lyon, head of operations for the Air Force's Air Combat Command.

The pressure vest was originally designed for use by pilots of older fighters, like the F-16 Viper and the F-15 Eagle, and is designed to protect the pilot from the strains associated with pulling extremely high-Gs and emergency de-pressurization at high-altitudes.

"What we also found in our testing that we did this spring and early summer, was that the functioning of that valve was specified to work in an F-15 or an F-16 but it's not specified to work with an F-22," said Lyon during a July 31 briefing at the Pentagon. "That valve is opening under normal conditions in an F-22, when it should not."

When worn by pilots flying older fighters, the vests normally draw air from their jets' oxygen systems only when the planes' pull more than four-Gs, explained Lyon. However, the Raptor's system constantly pumps oxygen to the pilots from the time they enter the airplane, a feature designed to protect pilots flying through air contaminated by chemical or nuclear warfare, as well as providing more air to them at extremely high altitudes. As a result, "this vest is always inflated on an F-22 pilot, and it should not be inflated until they start to pull Gs. What that does to the pilot is, it restricts his breathing, and it restricts his ability to do normal inhalation and exhalation," Lyon said.

The Air Force is remedying the problem by developing a new high-tension valve that will only allow the vest to inflate when the pilot is pulling high-Gs. The new valve will be distributed throughout the Raptor fleet by the end of 2012 if all goes well in testing, according to Lyon. He declined to say how much the fix  would cost, other than saying it would be in the millions.

What about other incidents where F-22 pilots -- and some ground crew -- reportedly suffered from hypoxia like symptoms that weren't traced to the faulty valve and vest combination? Well, since the Air Force exhaustively screened them for toxins and found nothing, it is blaming those incidents on dehydration, under-nourishment, or breathing too much jet exhaust.

The service began investigating the hypoxia-like symptoms after a Raptor crashed in Alaska in November, 2010 while the pilot was reaching to turn on his emergency oxygen system.

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The world's other biggest blackouts

India's dark days continue. When two of the country's five power grids collapsed today, the number of powerless Indians neared 700 million. With stranded trains, unresponsive ATMs, and dark traffic lights abounding, it's been an unprecedented disaster only somewhat mitigated by the fact that the majority of Indians aren't connected to the power grid in the first place. 

India's outage is now the largest blackout in history, surpassing yesterday's power outage for the record. But it's not the only time the world has seen millions without power. Here are a few more of the world's recent memorable blackouts:

Indonesia: Aug. 20, 2005

Number affected: 120 million people in Java and Bali

When three power stations went down, three provinces -- including the capital city, Jakarta -- were plunged into darkness. Fires erupted across the capital when resourceful residents turned to candles to light their homes.

Brazil: March 12, 1999

Number affected: 97 million across Brazil and Paraguay

The blackout was caused by lightning hitting an electricity substation, causing the cities of Sao Paulo and Rio de Janeiro to grind to a hault. Just two years later, the Brazilian government was forced to ration power to prevent more blackouts during a national drought.

Brazil: Nov. 10, 2009

Number affected: 60 million across Brazil and Paraguay

Ten years after Brazil's biggest blackout, the Itaipu dam along the border of Paraguay shut down completely, affecting large parts of both countries. Many at the time thought the blackout (shown above) was the consequence of a cyberattack.

Italy -- Sept. 28, 2003

Number affected: 57 million across Italy

The blackout occurred the night of Italy's annual "Nuit Blanche" or "White Night" festival in Rome. It's safe to say festivities ended earlier than expected.

United States -- Aug. 14, 2003

Number affected:  50 million in New York, Michigan, and Ohio, as well as Toronto and Ottawa, Canada 

The biggest blackout in U.S. history cost an estimated $6 billion dollars. Remarkably, the massive outage began with a single high-voltage power line in Northern Ohio brushing against overgrown trees.

United States -- Nov. 9, 1965

Number affected: 30 million across parts of Connecticut, Massachusetts, New Hampshire, Rhode Island, Vermont, New York, New Jersey, and Ontario, Canada

The initial cause of the blackout was the tripping of a transmission line near Ontario, though at time, many linked the outage with supposed UFO sightings.

Europe -- Nov. 4, 2006

Number affected:  10 million across Europe

After a routine shut down of a high-voltage transmission line to allow a ship to pass on the Elms river in Germany supposedly caused this blackout.  France, Italy, Austria, Belgium, and Spain were also affected.

Northeast Brazil -- Feb. 4, 2011

Number affected: 10 million

Keeping the lights on does, indeed, appear to be an Achilles heel for the fast-growing economy, provoking fears ahead of the 2014 World Cup and 2016 Olympics.

MAURICIO LIMA/AFP/Getty Images