  The separation assurance task will be extremely challenging for air traffic
controllers in a complex and high density airspace environment. Deep
reinforcement learning (DRL) was used to develop an autonomous separation
assurance framework in our previous work where the learned model advised speed
maneuvers. In order to improve the safety of this model in unseen environments
with uncertainties, in this work we propose a safety module for DRL in
autonomous separation assurance applications. The proposed module directly
addresses both model uncertainty and state uncertainty to improve safety. Our
safety module consists of two sub-modules: (1) the state safety sub-module is
based on the execution-time data augmentation method to introduce state
disturbances in the model input state; (2) the model safety sub-module is a
Monte-Carlo dropout extension that learns the posterior distribution of the DRL
model policy. We demonstrate the effectiveness of the two sub-modules in an
open-source air traffic simulator with challenging environment settings.
Through extensive numerical experiments, our results show that the proposed
sub-safety modules help the DRL agent significantly improve its safety
performance in an autonomous separation assurance task.
