An Icon Aircraft A5—the innovative amphibious aircraft that only recently entered production—crashed early Monday on the shores of Lake Berryessa, in Napa County, California, killing the company’s lead aeronautical engineer, Jon Karkow, 55, and his colleague Cagri Sever, 41. The crash of the aircraft, known for its forgiving flight characteristics, folding wings, and appeal to recreational pilots, serves as proof that aviation remains a dangerous pursuit.

The cause of the crash remains unknown, and the National Transportation Safety Board is investigating. Icon CEO Kirk Hawkins called the loss devastating. “The thoughts and prayers of our entire organization are with the families of both people onboard, they were both truly amazing individuals," he said in a statement.

Karkow, a highly regarded engineer, spent more than two decades with Burt Rutan’s Scaled Composites, an outfit known for designing unconventional aircraft. There, Karkow led the development of more than 20 aircraft programs, including adventurer Steve Fossett’s Virgin Atlantic GlobalFlyer. (Fossett flew the plane around the world twice, setting multiple records.) Karkow, also the program’s chief test pilot, won a 2006 Aeronautics Laureate Award from Aviation Week & Space Technology for the achievement. He worked on the development of SpaceShipTwo, the commercial suborbital spacecraft being developed by Richard Branson’s Virgin Galactic, before joining Icon about nine years ago.

With Karkow on board, Icon designed the A5 to appeal to beginner and recreational pilots, creating a spin- and stall-resistant design. Karkow built the wing to remain stable even when airflow is disrupted over certain areas, which can happen when the aircraft flies too slowly or if the wings are pitched too vertically—situations that can send aircraft spiraling downward.

The A5 made its maiden flight in 2008, and in 2012 became the first aircraft to meet the FAA’s new spin-resistance standard. Made largely of carbon fiber, the A5 can take off from land or water, and folds its wings rearward for easy storage. Icon bills the $190,000 A5 as a weekend getaway aircraft, with a 345-mile range but a top speed of only 121 mph.

The fatal crash is particularly distressing given the safety-first design of the aircraft, and Karkow’s experience piloting far more radical aircraft while at Scaled Composites. It’s unknown whether Karkow was testing or demonstrating the spin-resistance of the wing design at the time of the crash, and whether that or another flaw or structural failure contributed to the accident. The destruction of the aircraft on the lakeshore, visible in photographs, suggests a steep vertical descent. The National Transportation Safety Board expects to publish a preliminary report by the end of next week.

Whatever its cause, the crash will likely prove a significant setback for Icon, which has struggled lately with financial and production issues. Last year, it laid off workers and reduced production expectations from 175 aircraft to just 20.

Karkow and Sever are the latest in a long line of pioneers to lose their lives exploring new ways to fly, and their deaths are a reminder that even in the 21st century, leaving the ground doesn't come with a guarantee of a safe return.