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The Sikorsky CH-53K’s entry into low-rate production has been delayed again, this time by eight months to February 2017, because of gearbox failures last year and the late delivery of parts from suppliers, the US Government Accountability Office (GAO) reports in its annual assessment of Pentagon weapon projects.

The King Stallion development effort achieved first flight last October – "nearly three years later than originally planned" and five years after completing its critical design review.

In January, the second test model began flying at Sikorsky's facility in West Palm Beach, Florida and the GAO report notes that it contains the improved gearbox that was first trialled on a ground test vehicle.

“The unexpected redesigns of the aircraft's various gearboxes, as well as the late delivery of some components, have delayed delivery of the remaining two engineering design model test aircraft,” the GAO states in its 31 March report. “This has created delays at the production facility where parts are received from vendors, which is expected to impact the flight test schedule.”

The supersized King Stallion heavy-lift helicopter will replace the US Marine Corps' Sikorsky CH-53E, which was introduced in the 1980s and has anticipated service life of 41 years.

The cost of developing the aircraft has grown by 44% from $4.7 billion to $6.8 billion since 2005 and the procurement estimate for 200 aircraft stands at $19 billion.

The date for completion of operational testing shifted nine months since the GAO's 2015 report, from September 2018 to June 2019.

Despite gearbox troubles and the reported production issues, the Marines still expect to have the first war-ready squadron in place by July 2019..

Sikorsky officials said at a recent press briefing that the CH-53K flight test programme expects to log about 100h in 2016.

The Lockheed Martin-owned helicopter manufacturer expects to complete the second and third flight test aircraft this year, to support performance, propulsion and avionics flight qualification.

US Naval Air Systems Command (NAVAIR) reported on 24 March that the King Stallion recently demonstrated its advertised speed of 140kts with 15° angle-of-bank turns.

“This marked the last test flight in direct mode,” NAVAIR says. “The primary flight control system work up included 120kts, climbs and descents and hovering pedal turns.”

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US Naval Air Systems Command (NAVAIR) reported on 24 March that the King Stallion recently demonstrated its advertised speed of 140kts with 15° angle-of-bank turns.

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