Automatic Landing Design for Overweight Transport Aircraft with Explicit Flare Controller and Incremental Backstepping

What is it about?

Emergency landings shortly after take-off require the dumping of fuel. However, when this system is not available, landing over the Maximum Landing Weight (MLW) causes longer down-times due to obligatory structural inspection or fatal accidents. This paper compares the performance of two controllers in order to achieve a guaranteed soft landing with minimum standard deviation in overweight landings: the Explicit Flare Controller (EFC) and Incremental Backstepping (IBS). EFC is a conventional approach which uses a Proportional-Integral (PI) controller to follow an explicitly defined flare trajectory, whereas IBS is an incremental nonlinear control method. Both control architectures are implemented in a transport aircraft and their performance is assessed with Monte Carlo-based risk analyses from the Acceptable Means of Compliance (AMCs) described in the Certification Specifications for All Weather Operations (CS-AWO). The controllers’ hyper-parameters are tuned with a hybrid optimiser that combines genetic algorithms and pattern search. Results show that EFC does not meet the required criteria without overweight, whereas IBS can deal with overweight landings without atmospheric disturbances.

Featured Image

Photo by Avel Chuklanov on Unsplash

Photo by Avel Chuklanov on Unsplash

Why is it important?

An aircraft is certified to land at a weight below its so-called Maximum Landing Weight (MLW), which may be well below its maximum Take-off Weight (MTOW). In case of a mishap or severe failure during early flight phases, the crew may decide to perform a precautionary early landing. Any excess fuel is then usually dumped by means of a dedicated system, or burned by loitering until the aircraft weight is below its MLW. This obviously has a negative impact on the environment. In urgent cases, the crew may decide to land above MLW. This poses a risk and has resulted in incidents and accidents in the past. In any case, it requires taking the aircraft out of service for some time to perform inspections to the structure and landing gear. Well-designed automatic landing systems have low dispersion in touch down location and velocity and tend to have relatively accurate and predictable flare behaviour under all allowable operating conditions. This work explores a newly developed advanced control system that inherently covers over-weight landing cases. Risk levels can be maintained that are comparable to normal cases, landing above MLW may become a safe and economically acceptable alternative even in less urgent cases, reducing environmental impact of fuel dumping over land or sea.