https://www.mdpi.com/2226-4310/11/3/230
Authors. Andris Slavinskis and colleagues
Venue. Aerospace 11:3 , article 230
How the Institute flags it
frontier 1 time speculative 1 time
This source carries more than one flag across the corpus. That is not an inconsistency to resolve: the same work can be established evidence for one claim and frontier evidence for another, and the flag belongs to the use rather than to the source.