Dear Philippe,
I have some additional information for you from my sources and from a book I found: "Phoenix Triumphant-The Rise of the Luftwaffe" by E.R.Hooten. It is mostly about the Luftwaffe prior to WW2, but has some good background information on German air efforts before the rise of Hitler.
It states that Sachsenberg was in the process of demobilizing the Marine Jagdgeschwader in Dessau, when approached by Gen.Rudiger Graf von der Goltz (the commander of the Freikorps Baltiks)in Jan.1919 about forming a volunteer air force to serve with his unit.
Sachsenberg formed his new Geschwader at Juterbog (SW of Berlin), which by late Feb.1919 was mobilized and in Latvia to the east of Riga, where it served under the command of the 1.Garde Reserve Division (the actual name of the so-called Iron Division).
It consisted of three squadrons:
FFA 413 equipped with Rumpler C.IV aircraft, which were used in support missions--recon and for dropping supplies to the rapidly moving ground units.
FFA 416 (later known as Freiwilligen Jasta 416) equipped with the Junkers D.I and some Fokker D.VII fighters. There were few Bolshevik fighters to worry about, so this unit served mostly as scouts and attacking random ground targets.
FFA 417 (later known as Freiwilligen Schlasta 417) equipped with Junkers CL.I aircraft, which was used primarily for close ground support, often engaged in low level attacks on Bolshevik ground columns, armoured trains, and supply depots. This unit could also assist with missions similar to FFA 413 as described above.
Sachsenberg was said to be impressed with the all-metal Junkers because of the punishment those aircraft could take from anti-aircraft fire and still remain airworthy.
Other units served in this operation also. Schoenebeck commanded FFA 421 and
Bruno Loerzer led FFA 427. Fliegergeschwader Weinschenk was comprised of FFA 424, 425, 426, and (later) 433.
When von der Goltz was forced to resign, he was replaced by Gen.Ltn. Walter von Eberhardt who had been the first Idflieg in 1913-1914. By that time, the political situation had worsened back home, no new supplies or reinforcements were forthcoming, so by Dec.1919, von Eberhardt was forced to withdraw into what was then the German territory of East Prussia. So ends the Baltic adventure of the Freikorps. Hope this was of help to you.
Best Wishes,
Gary