The world's largest aircraft crash landed at the end of its second test flight on Wednesday.

The 300-feet long Airlander 10 nosedived on its return to an airfield north of London after spending more than an hour and half in the air.

"The Airlander experienced a heavy landing and the front of the flight deck has sustained some damage which is currently being assessed," Hybrid Air Vehicles, the British company behind the aircraft, said in a statement.

The company did not explain what caused the crash but said all planned tasks were completed during the flight. The pilots were unhurt, it added.

The U.K. government's Air Accident Investigation Branch has begun an investigation, a spokesperson said.

Part airship, part helicopter, part plane, the aircraft is about 50 feet longer than the biggest passenger plane.

Airlander completed its maiden test flight just last week. But that was not without incident either.

The flight was postponed for three days due to a technical problem, and then when Airlander took off -- after hours of delay -- it only stayed in the air for 20 minutes instead of the 90 minutes originally planned.

Related: World's largest aircraft completes its first flight

Airlander has four engines and no internal structure. It maintains its shape thanks to the pressure of the 38,000 cubic meters of helium inside its hull, which is made from ultralight carbon fiber.

Together with the aerodynamic shape of its hull, the lighter-than-air helium gas provides most of the lift. The aircraft's odd shape has led some observers to describe it as a "flying bum."

The aircraft was originally designed for U.S. military surveillance. But the project was grounded in 2013 because of defense spending cuts.

Hybrid Air Vehicles then managed to raise over 3.4 million pounds ($4.4 million) through two crowd funding campaigns. It also received a grant from the European Union and funding from the U.K. government.

Airlander is designed to stay airborne for up to five days at a time if manned, and for more than two weeks if unmanned. It should be able to carry up to 10 tons of cargo at a maximum speed of 91 miles per hour.

-- Laura Perez Maestro contributed reporting.