The CH-53K and the software upgrade process

By Robbin Laird

A key difference between 20th century legacy military platforms and 21st century platforms concerns software scalability.

With legacy platforms, integration on the platform was done by additive change, with then the need to modify the platform in different ways to accommodate the additive change.

With software-defined platforms, upgrades involve modifying the software, often to provide functionality that platform users suggest from actual operational experience.

Crafting ways to achieve transient software advantage and rapid insertion of technological advancements is key to a 21st century software fighting force.

The CH-53K in common with aircraft developed with a digital base are aircraft under continuous development even though they are part of the task force.

This means that with the software developments of the systems on the aircraft, the capability of that aircraft evolves over time.

And this process is very different from legacy aircraft, like the previous CH-53.

Software development teams are a key part of the aircraft’s continued evolution, and these teams combine user and government input with the aircraft prime contractor to perform code rewrite and development. in collaboration.

Recently, NAVAIR published an article on the CH-53K that highlights this process and its key benefits for driving innovation. The article was published on August 2, 2022 and was titled “Collaboration Enhances CH-53K Flight Control System Success.”

This article follows:

A full-authority digital flight control system (FCS) is one of the many impressive capabilities that sets the CH-53K King Stallion heavy-lift helicopter apart from any other heavy-lift aircraft. “Full Authority” means that the FCS provides all aircraft movement – not just to supplement the pilot for stability.

A digital fly-by-wire FCS is an electronic flight control system combined with a digital computer that replaces mechanical control systems in an aircraft. It makes the aircraft easier to handle in degraded visual environments at gross weights up to 88,000 pounds. The CH-53K is currently cleared to 27,000 lbs. external elevator but will eventually be cleared to 36,000 pounds.

“The CH-53E/Ds were much harder to fly,” said retired Lt. Col. Lucas Frank, formerly of Marine Operational Test and Evaluation Squadron 1 (VMX-1). “And the ease of piloting, the flight control system is probably the biggest game changer for the 53 community. We’re not used to that kind of stuff.

The high performance of the FCS is a direct result of the continued collaboration and cooperation among subject matter experts within the Naval Air Systems Command (NAVAIR) Heavy Lift Helicopters Program Office (PMA-261), Integrated Test Team (ITT) and the Flight Control Systems Design Engineers of Sikorsky, a Lockheed Martin Company.

For pilots, FCS provides more predictable and stable control responses to improve mission safety and efficiency.

For maintainers, FCS reduces complexity by eliminating conventional helicopter hardware like mixers, push rods and tail rotor cables, while improving diagnostic capability and maintenance time.

For members of the CH-53K ITT, the most impressive FCS advantage is how it can be used to achieve future capabilities and quickly correct identified deficiencies.

The CH-53K flight test program uses four Engineering Development Model (EDM) CH-53K aircraft. In these four-test aircraft, the fly-by-wire FCS allows the use of adjustable parameters called flight test variables (FTVs), giving the test team the ability to improve the control characteristics of the aircraft. plane.

“FTVs are an extremely powerful tool,” said CH-53K deputy program manager for testing Craig Merriman. “It allows us to test design fixes on aircraft between major software releases.”

According to Merriman, this means the team can continually improve the FCS software. If a problem is identified during the flight test, the FTVs can be adjusted within a pre-approved range, providing pilots with the ability to assess the correctness of the aircraft in the intended environment. These FTVs are then integrated into the next major version of the FCS software.

“With every major FCS software update, baseline aircraft performance increases significantly due to the incorporation of these verified FTVs,” Merriman said.

The CH-53K FCS is a work in progress and a team effort. When issues were identified during flight testing that needed quick resolution, the entire team worked together from locations in Florida, Maryland and Connecticut.

An example of the team’s success was fixing air data flaws during in-flight refueling. During initial in-flight refueling tests on the CH-53K in 2018, the FCS showed flaws due to turbulent air data created by the tanker aircraft. The FCS air data computers were reading large pressure fluctuations, leading the FCS to believe that the air data computers had failed.

With the shortcoming identified by the flight test team, design engineers began developing FTVs and performing analysis. The FTVs were evaluated in the Flight Controls System Integration Lab (FCSIL), a Sikorsky-owned lab in Stratford, CT, used by ITT. FCSIL is a representative CH-53K aircraft laboratory and simulator with triplex redundancy – a representative flight control system. The facility is used to simulate aircraft behavior and evaluate aircraft performance against newer FTVs. The facility is also used to verify the safe loading and unloading of FTVs to the software.

Following FCSIL testing, the NAVAIR Airworthiness Group reviewed the analysis and granted clearance to fly the FTVs. With this approval, the test team loaded the FTV onto the aircraft. The fix has been tested without degradation, enabling the fleet aerial refueling operations that are used today.

“It’s a very intuitive flight control system,” Frank said, “and it blends really well with the pilot and the computers. It lets you bypass the computer. And then the second you stop replacing it, the computer takes over without any further driver intervention. This is probably the biggest game changer for our community.

The use of FTV has been critical in addressing FCS shortcomings discovered during flight testing and will be used to enhance the already successful electric flight system as the CH-53K takes on additional capabilities in the future.


All the interest of the crucial advantage that a platform designed from scratch in terms of software scalability is put forward.

According to Merriman, this means the team can continually improve the FCS software. If a problem is identified during the flight test, the FTVs can be adjusted within a pre-approved range, providing pilots with the ability to assess the correctness of the aircraft in the intended environment.

full stop,

Feature Photo: A CH-53K King Stallion aircraft hooks up a refueling drug behind a KC-130J in-flight refueling tanker during a test over the Chesapeake Bay in 2021. Credit: NAVAIR.