During his nine-year tenure in the U.S. Navy, Richard Webb flew F-14 Tomcats. “The jets made famous in Top Gun,” he says, casually.

The only other thing that comes close to the experience of flying fighter jets, says Webb, is wingsuit BASE jumping. “It’s the same level of intensity," he says. "This sport brings back flashbacks of what I experienced landing a jet at night on the pitching deck of an aircraft carrier in the middle of a storm."

"That immense mental focus: You couldn’t trip, you couldn’t clutch—you had to dig deep and nail it.”

Wingsuit BASE jumping, an activity that’s little more than a decade old, is considered the most dangerous sport on earth, in part due to the frequency of high-profile deaths of very experienced pilots. The most recent victims: Dean Potter and Graham Hunt , two of the most accomplished wingsuit BASE jumpers in the world. The duo died together in a wingsuit accident in Yosemite National Park on May 15. ( Read about how Potter reinvented climbing and jumping .)

Simply “BASE jumping” is the act of parachuting from “fixed” objects. (BASE stands for the types of things participants leap off: buildings, antennas, bridge—spans—or the earth itself, in the form of cliffs or promontories.) The sport is estimated to yield one fatality for every 60 participants, according to a 2008 study .

Wingsuit BASE jumping, meanwhile, combines a BASE jump with the demanding skill of flying a wingsuit, a full-body rig that resembles a flying squirrel costume. Wingsuit BASE jumpers can reach speeds of more than 100 miles per hour and often fly close to cliff faces and other terrain, which adds to both the thrill and the danger.

There are no official participation numbers for either the sport of BASE jumping or wingsuit BASE. Tom Aiello, the owner of one of the few places that teaches the sport, the Snake River BASE Academy in Twin Falls, Idaho, estimates there might be 3,000 moderately active BASE jumpers in the world.

“Roughly, we’ve seen the sport double in growth over the last decade,” he says.

Matt Gerdes, the chief test pilot of the U.S.-based wingsuit company Squirrel —one of only a handful of wingsuit manufacturers in the world—estimates that there might be as many as 400 people in the world wingsuit BASE jumping.

Lower Cliffs, More Dangerous Jumps

Webb has been BASE jumping and parachuting for two decades but only took up wingsuit BASE jumping three years ago. He feels uneasy to be counted as a member of that elite group.

“I am not that experienced when compared to the level of talent out there crushing the Alps," he says. "We just happen to have gotten a little attention by being lucky enough to live in Moab and push the limits here a bit.”

Webb, 42, works as an airplane pilot and lives in Moab, Utah, which is regarded as one of the BASE-jumping capitals of the world for its numerous cliffs, endless canyons, and legal access.

In national parks, where most of the tallest cliffs in the U.S. are located, deploying a parachute is illegal, for safety reasons. Still, people do it, and they are rarely caught. There were only four incidents of arrest for BASE jumping in national parks last year, according to National Park Service spokesman Jeffrey Olson.

But Aiello guesses that on any given day of the year, someone, somewhere, will BASE jump in a national park, weather permitting.

Those who choose to jump within national parks reportedly do it at times they are less likely to be caught—during the night, or at dusk, when visibility is low. For example, last year some BASE jumpers privately attributed the death of Sean Leary , a well-known wingsuit pilot in Moab, to flying in low light inside Zion National Park, where he would’ve been fined if he’d been caught by rangers.

For those who don’t wish to break the law, the answer is either go to Europe, where BASE jumping is legal in many places with high, shear cliff faces, such as Mount Kjerag in Norway or the Eiger in Switzerland, or seek out other locations in the U.S. where jumping is legal. That usually means wilderness areas controlled by the Bureau of Land Management.

But that also means lower cliffs, which translates into more dangerous jumps.

Short Leaps in Moab

“I don’t have the luxury of being able to take time off work and go on a very expensive wingsuit vacation to Europe,” says Webb. “We have to work with what we have here.”

Across the Moab region, most “exits” (the spots from which BASE jumpers leap) are found atop cliffs in the range of 300 to 400 feet tall—a barely adequate height for BASE jumping, and widely considered much too short for wingsuit flights. (A 300-foot fall without a chute takes only 4.32 seconds.)

Until now.

After years of training, scouting, and planning—not to mention the arrival of vastly improved wingsuit technology—Webb and wingsuit partner Matthew Fleischman have begun wingsuit BASE jumping in Moab.

“Moab is like the mini golf of wingsuit BASE,” says Squirrel's Matt Gerdes. In Europe wingsuit BASE jumpers log 5,000 vertical feet of descent with flight durations lasting more than three minutes. In Moab, the flights might last between 20 and 30 seconds at most, which means the margin for error is extremely thin.

“These jumps are super difficult and super dangerous,” says Aiello.

Gerdes estimates that there are only 25 or 30 people in the U.S. who could safely wingsuit BASE jump Moab.

Webb and Fleischman now find themselves in that group. But they say their approach is unique.

“We’re not in the YouTube, GoPro generation of yahoos where it’s like, ‘Dude, go for it, you’ll stick it!’” says Webb. “We were the first people to put the effort into making sure we knew it was going to work. And then actually doing it.”

Webb, who has a degree in aeronautical engineering, approached wingsuit BASE jumping like an engineer. Using laser range finders, GPS devices, and an inclinometer, he and Fleischmann developed a model of data collection that helped them calculate whether flying from a particular exit point was mathematically survivable.

Most BASE jumpers rely on the “rock drop” method for determining cliff heights: drop a rock, count the seconds before you hear it hit the ground, and crunch the numbers. (For math geeks, the exact equation used to determine cliff height, in meters, is to take the time in seconds that the rock falls, square it, multiply it by 9.8, and divide it by two.)

“When the margins are tight, we prefer a laser,” says Webb.

Webb and Fleischman began by scouting potential exit points around Moab. While the sandstone cliffs of this region rarely exceed 500 vertical feet, they do have one feature going for them. They are often perched atop steeply graduated slopes of reddish dirt and boulders that offer up to another 1,500 vertical feet of relief.

The pair realized that if they could fly fast and far enough, they could wingsuit BASE jump in locations that might have seemed impossible.

Using GPS devices to record their wingsuit flights at safer locations such as cliffs in Switzerland, and other places in the United States, jumping from both cliffs as well as hot-air balloons, Webb and Fleischman slowly built up a database of their own flight profiles, including temperature, wind direction and speed.

They also measured how quickly they started flying forward and how far they flew in total, crunching all the data to create charts depicting the precise trajectories of their flights.

Modern Suits Yield Longer Flights

Another enabler of Webb's and Fleischman's dangerous Moab jumps: Wingsuits have come a long way since they were first made commercially available in 1999.

A nylon wingsuit contains a series of baffled chambers between the arms and the torso and between the legs. After jumping, the pilot spreads his arms and legs, and an air scoop fills the chambers with air in the first moment as the pilot descends. Once the suit is inflated, the pilot begins gliding forward faster and farther than he or she is descending and has a greater ability to steer through the air by adjusting body position.

The earliest wingsuits flew at a 1:1 glide ratio, meaning a pilot traveled forward one foot for every foot of drop. Design improvements have yielded suits with up to a 5:1 glide ratio, allowing pilots to set records for both distance and duration.

New designs also made suits inflate more quickly. “Just a few years ago, it took four or five seconds to start flying well,” says Webb. “Now we’re flying well in two to three seconds. That was unheard of.”

Quicker start, better suits, and higher glide ratios convinced Webb that “wingsuit technology was rapidly approaching what was needed to wingsuit in Moab.”

After several flights abroad, Webb and Fleischmann returned to Moab and set out to profile the terrain they wished to fly. They used a laser rangefinder, a sighting tube, and an inclinometer to measure and map the terrain as precisely as possible. After gathering this data, they compared the terrain to their own “worst-case” scenarios based on previous flights.

The data revealed that wingsuit BASE jumps were possible. Theoretically.

“Oh, I was terrified. Absolutely terrified,” says Webb of the moment two years ago when he stood at precipice of the first flight. “We emphatically knew, numbers-wise, that it could be done. It was just about digging deep enough to force your body to commit and make it happen.”

Three. Two. One. See ya.

Fleischman jumped first. Then Webb. They spread their arms, and the baffles of their wingsuits became stiff with air. Within seconds they were flying forward at 100 miles per hour, tracking their line, staying calm and focused as the rock-strewn ground whizzed by just a few dozen feet below. Soon the terrain dropped away, and the two men pulled their parachutes, abruptly ending their flights, descending to the valley floor.