NEW YORK — Flying on a commercial jet has never been safer. It will be four years on Tuesday since the most recent fatal crash in the United States, a span unmatched since propeller planes gave way to the jet age. Worldwide, last year was the safest since 1945, with 23 deadly accidents and 475 fatalities, according to the Aviation Safety Network. That was fewer than half the 1,147 deaths, in 42 crashes, in 2000.
Flying has become so reliable that a traveler could board a plane every day for 14,000 years without ever being in an accident, according to a calculation by the International Air Transport Association.
There are many reasons. Planes and engines are 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 share much more information about flying hazards, with the goal of preventing accidents rather than just reacting to them. And when crashes occur, passengers are more likely to get out alive.
‘‘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, chairwoman of the National Transportation Safety Board. ‘‘That’s not the case anymore.”
The grounding of the Boeing 787 fleet last month illustrates this new era of caution. The last time a fleet was grounded was in 1979, after a McDonnell Douglas DC-10 crashed after takeoff 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, in 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 2001, killing all 260 people on board.
But flying is 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 US 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 rest periods for pilots. But in the face of opposition from airlines, it is still working on new rules for more extensive copilot 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.