The Pentagon and Sikorsky are keeping mum on the CH-53K King Stallion’s production go-ahead decision, which was scheduled for a high-level review last week.

The US Marine Corps’ CH-53K was slated for a decision to launch low-rate initial production on 30 March, but Sikorsky and the US Navy’s programme manager for heavy lift helicopters would not comment on the decision during the annual Sea Air Space conference outside Washington this week

“We’re just waiting for OSD [the office of the secretary of defense] to come out and say what they need to say,” US Marine Corps Col Henry Vanderborght told reporters 3 April. “I can tell you officially, we’ve purchased material for low-rate initial production lot 1.”

A Pentagon spokesman did not elaborate on the reasoning behind the delayed Milestone C decision.

“Results of defense acquisition board meetings are pre-decisional, until they are completed, documented and approved by the Defense Acquisition Executive (DAE),” the spokesman says. “It would be inappropriate to comment at this time because we do not want to get ahead of the requirements that are part of the approval process.”

Sikorsky has not yet finalised its design for the CH-53K, a company spokesman tells FlightGlobal. Operational testing scheduled in 2019 could discover additional components requiring changes, she adds. The Pentagon does not require Sikorsky to finalise its design before milestone C and additional changes could be made as needed following testing.

Meanwhile, Sikorsky has largely solved several outstanding issues on the King Stallion, including engine flameouts and main rotor damper overheating pointed out in a 2016 report from the Pentagon’s top weapons tester. The helicopter experienced a few flameouts in the second engine, though none during flight, he says. Flameouts occurred when the pilot landed the aircraft, reduced its power and attitude on the runway. The USMC tried to recreate the problem in the air by going beyond the level attitude after a certain time in flight, but the service could not replicate the issue.

“Basically we instrumented the fuel lines on the number two engine and what we found is that because of vibration or some other condition, air would come out of solution of the fuel and we basically get trapped in the geometry of the fuel lines in the aircraft,” he says. “As soon as you went to a condition of low power on the ground and level attitude, that air would go into the engine and cause the engine to flame out.”

The helicopter operates at a higher power setting while flying and couldn’t repeat the flameout since there’s more pressure for the fuel moving toward the engine, Vanderborght says. That column of air moves through the engine and has no effect. The USMC is already working on a more powerful engine rivet suction pump that should fix the issue, he adds.

“It’s already at GE in the test cell working and now it’s just a matter of flying with it on the airplane,” he says. “That pump will increase the pressure of the fuel going to the engine and prevent some of these flameouts here.”

Modifications to the second engine compartment have resolved most of the engine overheating issues, Vanderborght says. Sikorsky maintains the problem is gone but hasn’t finished testing, which will wrap in spring of 2019, says Michael Torok, Lockheed Martin’s vice president of CH-53K programmes. Sikorsky has also adjusted the rotor damper to ameliorate an issue with the helicopter’s aft center of gravity.