A Comprehensive Survey on Climate Optimal Aircraft Trajectory Planning

Round 1

Reviewer 1 Report

This is a very nice piece of work, carefully written and easy to read. I don't have anything relevant to recommend that would not be plain nitpicking, so I am happy to recommend this one for publication.

One minor editor thing: I think there is a category of papers on MDPI which are "Review" instead of "Article". I would recommend flagging this one as so.

Reviewer 2 Report

The purpose of this paper is to provide a comprehensive review of the state-of-the-art studies for the past two decades regarding climate impact optimal aircraft trajectory planning. Two major aspects are investigated in detail in order to mitigate the climate impact of aviation, namely how to integrate climate effects in aircraft trajectory planning and which methods are appropriate to generate optimized trajectories considering an objective function including climate effects. General aspects concerning the aviation-induced climate impact consisting of carbon dioxide (CO2) emissions and of non-CO2 effects are presented in the paper’s introduction. The climate impact of non-CO2 emissions and how they can be mitigated using operational strategies are discussed in the second section of the paper. Further, in Section 3, optimal control and non-optimal control approaches for the trajectory planning aiming to reduce aviation’s climate impacts are presented. In the fourth section of the paper, recent studies devoted to trajectory optimization through cost  and climate metrics are reviewed. Some challenging issues regarding the optimization problem statement taking into account climate metrics, aircraft dynamics and associated modeling uncertainties are discussed in the fifth section of the paper. The last section presents some concluding remarks.

The paper is well organized. Its topics are of interest surveying in a comprehensive manner recent relevant results regarding the aircraft trajectory planning under climate impact constraints.