Enabling steeper, more efficient glidepaths

The SESAR-supported STEPLESS project's high-lift system looks to ensure that increased glideslope angles can reduce noise without increasing emissions.

When an aircraft approaches an airport for landing, it typically uses a standard 3-degree descent path. But because such approaches are relatively close to the ground, they tend to be rather noisy and thus a nuisance for those living and working near the airport.

A quieter alternative is to increase the glideslope angle, which allows the aircraft to fly the final approach at a higher altitude.

"While increased glideslope angles have the potential to reduce both noise and emissions, they also demand specific aircraft capabilities that don't necessarily exist," says Dennis Vechtel, project coordinator at the German Aerospace Centre (DLR).

To enable low and therefore safe landing speeds, aircraft are equipped with a high-lift system that generates additional lift at low speed. The problem is that most of these systems only feature a few pre-defined configurations, meaning pilots have limited options for decelerating an aircraft's speed on a steep approach.

"To get the right amount of drag needed to decelerate, pilots must select a higher configuration or even use the landing gear earlier," adds Vechtel. "This in turn could lead to greater noise emissions, jeopardising any reduction in noise achieved from the higher flight altitude."

Another challenge is that today's fixed high-lift configurations aren't well-suited for conventional 3-degree approaches. This disadvantage is on full display when air traffic control (ATC) commands a fixed speed to ensure aircraft separation - a typical situation at most large and busy airports. "To follow this prescribed speed, especially on the glide path, pilots have no choice but to select the next higher high-lift configuration, with the resulting additional drag generating unnecessary fuel consumption and noise," explains Vechtel.

Addressing these challenges and helping reduce both noise and emissions during operations with conventional or even increased glideslope angles is STEPLESS.

Optimising a high-lift system's intermediate settings

The SESAR-supported project is developing a novel high-lift system that enables automatic and stepless adjustments to aircraft configurations during approach. "This will allow dynamic adaptations of the high-lift system to glideslope angles and flight conditions, ultimately improving energy management and enabling steeper, more efficient glidepaths," notes Vechtel.

To achieve this, the STEPLESS solution aims to optimise the intermediate settings of the high-lift system to better adapt the aircraft's glide performance to the prevailing approach conditions, such as wind, aircraft mass, or ATC constraints. It will also enable stepless adjustments of an aircraft's slats, flaps, and, potentially, speed brakes during descent and approach.

What makes this solution particularly innovative is that it allows a pilot to better manage the aircraft's energy, follow speed assignments by ATC, and fly as energy optimal as possible - even with increased glideslope angles.

Benefiting residents, airlines, and pilots alike

Started in 2024, the project focused its first year of work on integrating its high-lift system into the aircraft's overall architecture, an important first step to developing the system's individual functions.

"A key aspect of this work was to ensure that the high-lift system remains fully operational under all flight conditions, regardless of whether the autopilot is disengaged or the pilot deviated from the flight management system route," says Vechtel.

As the project progresses, it looks to further advance its solution by conducting several studies and tests. These include using flight simulators to understand how a pilot uses and interacts with the proposed cockpit's human-machine interface, as well as to evaluate new cockpit procedures and measure such potential benefits as reduced fuel consumption and decreased noise levels.

STEPLESS also plans to conduct an extensive fast-time simulation campaign to assess the broader impact these innovations will have at an air traffic management level.

Together, these activities mark an important step towards validating the project's concepts in realistic and scalable environments. "Once validated, the STEPLESS solution will reduce noise, fuel consumption, and cockpit workload to the benefit of residents, airlines, and pilots alike," concludes Vechtel.

Learn more about the STEPLESS project here.