Flying on a commercial jetliner has never been safer.
It has been four years since the most recent fatal crash in the United States, a span unmatched since propeller planes gave way to the jet age more than half a century ago. Worldwide, last year was the safest since 1945, with 23 deadly accidents and 475 fatalities, according to the Aviation Safety Network, an accident researcher. That was fewer than half the 1,147 deaths, in 42 crashes, in 2000.
In the last five years, the death risk for passengers in the United States has been 1 in 45 million flights, according to Arnold Barnett, a professor of statistics at MIT. In other words, flying has become so reliable that a traveler could fly every day for an average of 123,000 years before being in a fatal crash, he said.
There are many reasons for this development. Planes and engines have become more reliable. Advanced navigation and warning technology has sharply reduced once-common accidents like midair collisions or crashes into mountains in poor visibility. Regulators, pilots and airlines now share much more extensive information about flying hazards, with the goal of preventing accidents rather than just reacting to them. And when crashes do occur, passengers are now more likely to survive.
''The lessons of accidents used to be written in blood, where you had to have an accident, and you had to kill people to change procedures, or policy, or training," said Deborah Hersman, the chairwoman of the National Transportation Safety Board. "That's not the case anymore. We have a much more proactive approach to safety."
The grounding of the Boeing 787 fleet last month illustrates this new era of caution. The last time a fleet was grounded was 1979, after a McDonnell Douglas DC-10 crashed shortly after takeoff at O'Hare Airport in Chicago, killing 273 people. The 787s, by contrast, were grounded after two episodes involving smoking batteries in which no one was hurt and no planes were lost.
The last fatal accident involving a commercial flight in the United States was Colgan Air Flight 3407, which crashed near Buffalo, N.Y., killing 50 people, on Feb. 12, 2009. The pilot did the opposite of what he was supposed to do when ice formed on the wings.
Perhaps even more noteworthy, there has not been an accident involving a major domestic carrier since an American Airlines flight to the Dominican Republic crashed after takeoff in New York in November 2001, killing all 260 people on board.
But while flying is safer, it is still not risk-free.
Air traffic is set to grow in the next decade, and airports are more congested. Near-misses on runways and taxiways have risen. And with 2 million U.S. passengers boarding more than 30,000 flights every day, maintaining that safety record will be a challenge.
The Colgan accident also cast a troubling light on regional airlines, which hire young pilots, sometimes with little experience, at a fraction of the salaries paid by the bigger carriers.
Since the crash, the Federal Aviation Administration has mandated longer resting periods for pilots. But in the face of opposition from airlines, it is still working on new rules for more extensive co-pilot training.
''It's important not to define safety as the absence of accidents," said Chesley B. Sullenberger III, the US Airways pilot who became a hero when he landed an Airbus A320 in the Hudson River in January 2009 after both engines lost power.
All 155 passengers and crew escaped.
''When we've been through a very safe period, it is easy to think it's because we are doing everything right," he said. "But it may be that we are doing some things right, but not everything. We can't relax."
The FAA and airlines now systematically study data from flight recorders to analyze common problems, like finding the best angle of approach and speed to land at airports with tricky wind conditions.
Besides advances in navigation technology, today's airplanes are equipped with systems that can detect severe turbulence or wind shear, allowing pilots to avoid them altogether. Engines are also better built — when one fails, pilots can still land safely.
''We have engineered out the common causes of accidents," said Patrick Smith, a commercial pilot who writes a blog called Ask the Pilot.
And because planes have better hull and seat design, said Kevin Hiatt, the president of the Flight Safety Foundation, "crashes are more survivable today than decades ago."
In August 2005, for instance, an Air France flight to Toronto overshot the runway and burst into flames, yet all 309 passengers and crew managed to escape.
Aviation safety officials will also go to considerable lengths to learn what caused a crash. Uncertainty is rarely tolerated, said Peter Goelz, a former managing director at the National Transportation Safety Board.
After an Air France jet crashed in the Atlantic Ocean in 2009 on its way from Brazil to Paris, investigators spent nearly two years — and millions of dollars — looking for the flight data recorder.
''Aviation, in particular, abhors a vacuum," Goelz said.
Smith said there was another reason for the safety record: "Luck is always going to be a part of it."