I Watch the preview of this leg yesterday and i've got some Information. I lived near Paris so i know some things about the city and the suburb. The Route Info at "La ferté alais" with the plane task is not at Paris. La Ferté Alais is a small town in the South of Paris, in the countryside. To go to Ferté Alais, there is no direct bus from Paris, it's at 60km of the capital so the taxi will be very expensive. The only way to go la ferté alais is the rer D, a train line who run across the paris suburb. The problem is that la ferté alais rail station is on a poor trafic section (between Paris and Malesherbes). I take this section a few times and la ferté alais and some others rail station are on the countryside. For the direction between Paris and la ferté alais, there is a train every hour in the two sides. If you missed the train by a few seconds, you must wait 1h before the other train. If you finish the plane task with a big advance or a big delay, you must wait train so you could lose your advance or increased your delay. On the preview, we saw the rail station of La ferté Alais with a green line on a panel, sign of the rer D. So, probably a transportation drama!
Some other information with the nearest subway station near the route info:
Pont Alexandre III (RER c: Invalides)
Sacré cœur (Subway line 2: Anvers and Funicular to sacré cœur)
Place Charles de Gaulle étoile (a lot of connection)