Full system testing of the CH-53K heavy-lift helicopter being developed for the U.S. Marine Corps has begun, Sikorsky Aircraft said Thursday.

The testing involves a non-flying prototype with all seven main rotor blades and four tail rotor blades attached and spinning, the start of a two-year test program of the rotor blades, transmission, engines, and all sub-systems on the ground test vehicle.

"This is another key milestone in our building block approach to maturing the aircraft system," said Mike Torok, Sikorsky's CH-53K Program vice president. "The aircraft is now fully configured to proceed to the next series of system integration tests that will further validate the aircraft systems, such as rotors, drive, electrical, hydraulic, avionics and flight controls -- all leading to operational acceptance testing that will clear the flight aircraft for flight operations."

An initial flight test of engineering development CH-53K is expected late this year.

The CH-53K will be the newest variant of the Super Stallion, featuring three engines, composite rotor blades, and a wider cabin. It will have a cruise speed of 196 miles per hour and a range of 454 nautical miles. Its maximum gross weight with an external payload is 88,000 pounds.