Siemens

An electric plane crashed late last week, killing both pilots aboard, according to Siemens, which powered the plane.

The crash happened in Hungary on May 31 and involved an experimental Magnus eFusion aircraft. The cause of the accident is unknown.

"We cannot comment on eventual causes or any circumstances at this point of time," Siemens said in a statement. "We are working closely together with the authorities to clarify the cause of the accident."

The company said it decided to ground the aircraft until it learns the cause of the fatal accident.

The eFusion has lithium-ion batteries at the front of the plane, according to Engadget, which power Siemens' SP55D electric motor. The use of lithium-ion batteries has caused a stir, particularly after the FAA grounded all US Boeing 787 Dreamliner planes in 2013 after several failures. But there hasn't been any large-scale testing on the safety of batteries which directly power small plane motors, Engadget reports.