Safe2Land's motivation and solution

A complete engine failure faces pilots with significant challenges. Under immense time and psychological pressure, two main problems in particular must be solved: First, a suitable landing site must be identified and selected. Second, the glide trajectory to that site must be calculated precisely, as it differs significantly from an approach with engine assistance. If no official airport is within range, an appropriate emergency landing area must be chosen. Moreover, The calculated trajectory for the glide must adapt to changing wind conditions and thermals. In 2009, Captain Sullenburger had only 35 seconds to decide whether to return to LaGuardia. After this brief window of stress and uncertainty, his only option was an emergency water landing in the Hudson River. With Safe2Land, he would have received reliable and near-immediate support for a faster response.

With functioning engines, energy can be supplied at any time, while in a glide, only the available potential and kinetic energy of the aircraft, which continuously decreases, can be used. Therefore, it is necessary to model the aircraft's energy balance accurately so that the trajectory ends exactly at the runway threshold with the correct altitude and heading. Excess energy can be dissipated through specific flight maneuvers (e.g., appropriate leg positions and turns) or the use of flaps at the right points in the final. However, misjudgments of external conditions (e.g., wind or thermals) cannot be corrected by increasing thrust.

Currently available commercial landing assistance systems (such as Garmin, Foreflight, or SkyDemon) offer only limited support for these problems. Some systems (e.g., Garmin Autoland) still rely on engine power, while others only display the area that can be reached in a glide (e.g., Garmin SmartGlide or SkyDemon). Unfortunately that glide rings changes if turns must be flown in order to reach the final of an emergency landing spot. They are only correct if you glide straight ahead. Thus, an exact calculation of the glide trajectory does not take place, making these systems unsuitable for manual and fully autonomous flying. Likewise, no known assistance system provides data on emergency landing sites outside registered airports – a crucial factor when altitude above ground is too low for an extended glide.

The Safe2Land system we developed solves both of the above problems. By using pattern recognition techniques based on artificial neural networks, suitable emergency landing sites were identified from geodata (digital orthophotos, digital surface models, OpenStreetMap). For example, over 1,000,000 potential emergency landing sites have been identified in Germany by using DOM1 LiDAR geodata, which are stored in our emergency landing site database.

Based on our concept of kinematoide chains, glide trajectories are created that efficiently and precisely model environmental changes along any flight path. In this way we take air density or altitude wind vectors into account while computing a glide trajectory. Safe2Land generates control instructions in the form of target heading and target bank, which are presented to the pilot via a flight director. Additionally, we could also prove that the system enables fully autonomous landings by translating the guidance instructions into inputs for an autopilot. This has been successfully tested in a flight simulator.

In this web presentation, we will showcase the Safe2Land system using a workbench coupled with a flight simulator, allowing for quick evaluations of the trajectory algorithms. The parameters used for modeling the glide characteristics (e.g., optimal glide speed, glide ratios, wind direction, and strength at different altitudes) can only be estimated imprecisely and may change during the approach. Additionally, there are other interferences on the modelling: an overestimated glide ratio affects the glide performance similarly to a correct glide ratio combined with unexpected updrafts. With the workbench, we can examine how such disturbances can be compensated by adjusting the trajectory during the glide. For example, deploying the flaps earlier during the final approach can mitigate the effects of updrafts.

If these disturbances become too severe, a recalculation of the trajectory may be necessary. We recognize this need based on the predicted touchdown point relative to the (emergency) runway threshold, as determined by the kinematic chains. If, for example, the touchdown point is too far behind the threshold, the flaps are deployed earlier. Conversely, flap deployment is delayed or even omitted if the predicted touchdown point no longer lies on the runway.

In summary, Safe2Land provides reliable and immediate support for pilots in the event of an engine failure and due to its fine grain modeling by kinematoide chains it is even capable of performing the emergency landing fully autonomously via the autopilot.

Components of Safe2Land

Selected Presentations

Invited speech, IEEE BigComp Conference, Bangkok 2024

Emergency in an Austrian Alps' Valley

Deutscher Luft- und Raumfahrt-Kongress (DLRK 2024): 

"Dynamic adaptation and test bench evaluation of Engine-off emergency landing routes"