  Automated and autonomous driving has made a significant technological leap
over the past decade. In this process, the complexity of algorithms used for
vehicle control has grown significantly. Model Predictive Control (MPC) is a
prominent example, which has gained enormous popularity and is now widely used
for vehicle motion planning and control. However, safety concerns constrain its
practical application, especially since traditional procedures of functional
safety (FS), with its universal standard ISO26262, reach their limits.
Concomitantly, the new aspect of safety-of-the-intended-function (SOTIF) has
moved into the center of attention, whose standard, ISO21448, has only been
released in 2022. Thus, experience with SOTIF is low and few case studies are
available in industry and research. Hence this paper aims to make two main
contributions: (1) an analysis of the SOTIF for a generic MPC-based trajectory
planner and (2) an interpretation and concrete application of the generic
procedures described in ISO21448 for determining functional insufficiencies
(FIs) and triggering conditions (TCs). Particular novelties of the paper
include an approach for the out-of-context development of SOTIF-related
elements (SOTIF-EooC), a compilation of important FIs and TCs for a MPC-based
trajectory planner, and an optimized safety concept based on the identified FIs
and TCs for the MPC-based trajectory planner.
