Sikorsky has cleared the structural integrity of the CH-53K heavylift helicopter meets standards for first flight later this year.

The static test article (STA) was subjected to a round of proof loading tests, in which the US Marine Corps’ future airframe is loaded 115% over maximum design loads.

The tests are an encouraging indicator for the US military’s largest helicopter with a maximum take-off weight of 39,900kg (88,000lb), a 20% increase over the CH-53E Super Stallion it replaces.

Of six proof loading test conditions completed in 2013 and earlier this year, four were required before the CH-53K can attempt a first flight in the fourth quarter, according to Sikorsky.

The tests analysed loads on the tail rotor pylon at high and low speeds, the landing gear at ground impact and the full airframe at maximum rotor power, Sikorsky says.

Sikorsky also has completed ultimate load testing on two conditions, in which the main rotors are overloaded by 150% compared to design loads.

The event comes only weeks before the aircraft is scheduled to be rolled-out in a ceremony at the company’s West Palm Beach, Florida, assembly line and flight test centre.

The USMC plans to buy 200 CH-53Ks to replace a fleet of smaller and aging CH-53Es, filling a key role in the service’s heavylift strategy.

Although sharing the same designation and exterior design, the CH-53K is a substantially new aircraft, with a new rotor system, engine, transmission, cabin and tail rotor.

The USMC launched the development programme in 2005 with plans to enter service in 2015. But programme delays have pushed the initial operational capability milestone to 2018, even as the USMC has increased the programme from 156 to 200 helicopters.