Even though we may be done with the mystery of Flight MH370’s location, we’re on chapter one, page one in the story of what caused the crash. And that’s often a difficult question to answer. There aren’t always survivors to interview for clues. Even when authorities know the location of the plane, they still have to hunt for the flight data recorder and the cockpit voice recorder. And you can’t always attribute the accident to a single identifying factor as we could with that other ill-fated Malaysia Airlines flight, MH17, which was brought down by a missile in Ukraine last year.
That said, for the most part, plane crashes tend to break down into four main categories: mechanical failure, weather, intentional, and human error. What is the biggest factor in plane accidents? You might be surprised by the answer. Here, the top four causes of plane crashes explained.
A study by Boeing blamed mechanical failure for roughly 20 percent of today’s commercial air accidents (other studies have reached that same conclusion). But as aviation safety analyst, pilot and FAA Safety Team representative Kyle Bailey tells Yahoo Travel: “Mechanical failure isn’t as prominent as most people think.” While it seem like a high percentage, in the early days of flying it was the culprit in the vast majority of accidents, as many as 80 percent.
Bailey says we can thank improved airplane technology for the improvement. “The backup systems, the redundancy, and the computers pretty much are triple checking what pilots are doing,” he says. Plus, planes are being built better. “These airplanes aren’t like buying a $30,000 car; we’re talking about a $400 million 747,” Bailey says. “Each component that’s in there, every single component, is manufactured by an engineer to precise standards.”
In all, improved airplane technology is the factor most often attributed to the massive decline in accidents and marked improvement in commercial air safety in recent years. “The airplanes that are designed and built are so safe, even as a pilot it’s hard for me to comprehend how safe an airplane actually is,” Bailey says.
The National Transportation Safety Board finds weather is a primary contributing factor in 23 percent of all aviation accidents. “Whether it’s a small plane or a big plane,” Bailey says, “getting yourself into weather that’s a little bit above the scope of what an airplane can handle” often leads to trouble.
He points to last December’s crash of AirAsia flight QZ8501, which went down during a flight from Indonesia to Singapore, killing all 162 people aboard. Thunderstorms with cloud tops above 50,000 feet were reported in the area before the crash and are considered a possible factor.
“Those storms are going on every single day, all around that area, and [pilots] learn to weave their way through them,” Bailey says. “Ninety-nine percent of the time, they do a fine job. But there’s always that fraction of a percent that something will happen, something will go wrong, or you might misinterpret something and you’ll find yourself a little bit too close to or inside the thunderstorm.”
Thunderstorms, says Bailey, are especially treacherous. “[Planes] can withstand lightning,” he says. “But they can’t withstand going directly through a thunderstorm.” He adds hail, winds, updrafts, and downdrafts can wreak havoc with a plane, sometimes with disastrous results.
The numbers may vary, but the experts agree: Human error is the biggest cause of plane accidents. The focus is often on the pilots. PlaneCrashInfo.com analyzed 1,015 fatal accidents involving commercial aircraft, worldwide, from 1950 thru 2010, and found pilot error was a factor in 53 percent of all fatal accidents in that period.
“The planes are so complicated and sophisticated and have so many backup systems, [accidents] usually [are caused by] pilot error,” Bailey says. “If somebody comes up to me and says, ‘Planes are unsafe, blah blah blah,’ I’ll always say, ‘You shouldn’t be afraid of the plane, you should be afraid of the human element.’”
And when you add all human factors — mistakes by mechanics and air traffic controllers in addition to pilots — Boeing estimates human error in general might be a factor in as many as 80 percent of all airplane accidents.
Human error can also work in tragic concert with other leading causes of crashes — for instance, a pilot making a bad weather-related decision or making a catastrophic mistake while dealing with a mechanical issue. The latter may have been the case with TransAsia Airways Flight GE235, which crashed in Taiwan back in February (a widely seen video showed the plane clipping a bridge before crashing into a river), killing 43 of the 58 people aboard:
The plane’s troubles started when one of its two engines malfunctioned. But a critical mistake in the cockpit is what authorities believed caused the crash. “That was the pilot shutting down the wrong engine inadvertently,” says Bailey, echoing concerns that the TransAsia pilot shut off the working engine instead of the malfunctioning engine, causing the plane to stall.
Unfortunately, one can’t completely account for the human factor in plane incidents. After all, Bailey says, pilots are only people and not immune to the family stress, job pressure, fatigue, or inattention that can lead to disaster. “Things like that start to take their toll on the pilot and on everything running smoothly,” says Bailey.
An especially rare cause of plane disasters (accounting for 8 percent of all fatal plane accidents since 1950s, according to PlaneCrashInfo.com) is also one of the most frightening: intentional sabotage. The 9/11 attacks fit into this category, as does the more recent case of Germanwings Flight 4U9525, which a co-pilot purposefully crashed into a mountain back in March, killing all 150 people aboard. Bailey finds that case especially troubling. “Most pilots are highly dedicated people,” he says, “But obviously every pilot is a human being and you know, human beings have problems.”
You simply can’t look at scary aviation stats without acknowledging their most crystal-clear conclusion: that flying is incredibly safe and getting safer, despite high-profile accidents like Flight MH370. The International Air Transport Association says last year’s global jet accident rate was the lowest in history; the equivalent of one accident for every 4.4 million flights. The overall number of commercial airline fatalities also is near historic lows, despite the fact that the number of flights has increased dramatically in recent decades. That should be the gigantic grain of salt with which you take any scary stats about flying. 
Let Yahoo Travel inspire you every day. Hang out with us on Facebook, Twitter, Instagram, and Pinterest. Watch Yahoo Travel’s original series “A Broad Abroad.”
This article originally appeared on Yahoo!Travel and is republished here with permission.