"We are in the final descent."
Translation:Estamos en el descenso final.
In addition to "descent", "descenso" means "relegation", which means "the transfer of a sports team to a lower ranking division". https://en.wikipedia.org/wiki/Promotion_and_relegation Duolingo is apparently not using it in the sporting sense here, just giving us a random sentence.
Many private pilots view their passion of flying as a sport. I am a pilot. So, to also answer azizspanish, from above, when on the radio to the tower, I would report that, "I am on final approach (descent)," not "last approach (descent)." To use the word "last" is not incorrect English, it is just not proper vernacular for pilots.
I think the word "descenso" means a round of an elimination tournament, and that although it "relegates" a team or person to a lower level than the winners in that round, it also promotes the winners to the next, higher round. "The Sweet Sixteen" or the top eight, etc. Perhaps we Yankees have a triumphalist vision of the world, and focus on the winners to the extent that we quickly become unaware of the losers.