There have been many articles lately about how the chances of dying in a plane crash have never been smaller. But researchers have discovered deadly risks from Deep Vein Thrombosis, which often occurs during and after flying — a condition that is certainly are killing more people than plane crashes. Up to ten thousand per year.

It’s true 2017 was the safest year ever for air travel, with zero passenger airline fatal accidents on jets world-wide. There hasn’t been a fatal crash at a major U.S. passenger airline since 2009.

In the 1950s, the odds of an accident were about one in 50,000. Now the chance of dying in an airline crash is about one in 50 million, says Paul Hayes, director of air safety at London-based Flight Ascend Consultancy.

As travel expert Scott McCartney recently reported  in the Wall Street Journal.

We’re not so far removed from the days of a dozen fatal accidents world-wide and 700 to 1,000 deaths every year. Recent advances in aircrafts and airports, stiffer regulations and corporate changes at airlines and leasing companies are the top factors behind these results.

“It’s just stunning,” says William Voss, a safety consultant and former official at the Federal Aviation Administration and other major aviation groups. “I hope that we can sustain it, but that’s hard to do.”

What’s perhaps most remarkable: Accident rates in developing countries are dropping along with highly regulated, wealthy aviation markets, according to McCartney.

Of course this year’s statistics could be an anomaly, and crash death rates could spike upwards. Mr. Hayes says the 2017 results may give people a false sense of safety. Last year saw several near misses.

One that still troubles investigators: An Air Canada jet lined up to land on a taxiway in San Francisco rather than a runway, putting it on course for four planes waiting to takeoff. The jet came within 60 feet of the line of planes, the National Transportation Safety Board’s preliminary report showed, according to McCartney.

Today’s airplanes not only don’t break as often, they also have safety nets built in that override pilot error, much like cars that brake automatically to avoid collisions, safety experts say.

Big business also deserves some credit for reducing accidents. Major banks and large aircraft-leasing companies now make new planes available to airlines in less-developed countries at affordable prices.

To safeguard their investment, big leasing companies and banks require top-notch maintenance on planes, and monitor how airlines use them. That’s created an important check against cutting corners.

“You have a revolution in the business side,” Mr. Voss says. Leasing companies and multinational airline groups “have aligned the interests of big money to support safety, rather than undermine it.”

Among the good contributing factors are the global alliances and code-sharing partnerships, where one airline puts its own flight number on another carrier’s flight and sells the other airline’s seats to customers. Regulators require airlines to verify safety measures on partner airlines.

Some experts credit the European Union’s published “blacklist” of airlines considered unsafe for publicly pressuring carriers into improvements. The EU started publishing the list in 2006.

New systems and attention to the hazard have reduced runway incursions by about 90%, according to Arnold Barnett, a Massachusetts Institute of Technology statistics professor and aviation safety expert. Better warning lights at intersections of taxiways and runways have kept pilots from accidentally crossing in the path of planes taking off or landing. Ground radar systems warn air-traffic controllers when a plane is about to cross in the path of another, too. Installation is expanding. A runway monitoring system in Boston alerted controllers earlier this month when a United 737 entered a safety area as a JetBlue flight was close to landing.

Mr. Barnett thinks runway systems may be the biggest safety enhancement of the past few years.

But there are other deadly dangers from flying that are not clearly measured or calculated by crash statistics. It has been long known that airline passengers are likely to get injured or killed  by blood clots (Deep Vein Thrombosis) which develop when flying.

According to IATA, 3.5 billion people flew safely in 2015 without a crash. The American Heart Association, 1 in 1,000 people develop a DVT each year. Considering that the risks of developing DVT are greater for airline passengers, we can conservatively estimated that 3.5 million people developed a DVT after flying. Of course, not all of them died, actually from their DVTs, but certainly  tens of thousands did.

One estimate by renowned researcher, Dr. Suzanne C. Cannegieter of the Department of Epidemiology at Leiden University Medical Center in the Netherlands, roughly estimates that world-wide there were some 250,000 cases of air travel-related DVT in 2012. As approximately 5 percent of DVT cases are fatal, this would put the death rate at 12,500 last year.

The ailment can be fatal if the clot travels to the lung or heart, which happens in one third of the cases.

“Clots don’t form for one reason,” experts report. It takes a perfect storm of factors — age, immobility, genetics, recent surgery or hospitalization, long-distance flights or dehydration.

Liz Cooper, 32, a previously healthy restaurant manager, died just three hours after landing at Manchester airport in England. The cause of death was a pulmonary embolism due to deep vein thrombosis (DVT) of the right lower leg. She had a Factor V Leiden condition which made her four to eight times more likely to suffer a DVT. No one really knows, but it is estimated 30 million people in the US suffer from this genetic condition.

DVT often  includes unexplained pain, tenderness, redness and swelling in the leg. When a clot has traveled to the lung, common symptoms include chest pain and breathing difficulties.

But diagnosis and amazing statistics can be difficult if not impossible.

Some cases are asymptomatic or can mirror other illnesses. Leg pain can be mistaken for an athletic injury or strained muscle. Chest pain is often diagnosed as a heart attack or the flu.

There are tens of thousands of unexplained deaths by doctors that should be attributed to DVTs.

Some experts call death from DVT an “economy-class syndrome.” The condition affects people during or after long flights in economy class where legroom is limited. The longer the flight, the more at risk you are for developing a clot. Flights lasting 8 to 10 hours or longer pose the greatest risk.

Rep Steve Cohen (D-TN) pointed out DVT’s deadly dangers when he introduced a bill which would require the FAA to establish minimum seat size and distance between rows. In the last couple of years airlines have been shrinking seat sizes to cram more people in their planes and make more money.

Remember: if you want to live longer, move around a lot and fly in premium seats — with more space to prevent blood clots from forming in your legs. Drink plenty of water, stretch your calf muscles frequently and avoid tight clothing below the waist.

The U.S. Surgeon General has issued a Call to Action on DVT and PE to raise public awareness of these blood conditions and increase research on the causes, prevention, and treatment.

And don’t worry so much  about a plane crashes!

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