After completing his studies, he first went to the Deutsche Versuchsanstalt für Luftfahrt in 1926, where he remained until he moved to Brandenburgische Motorenwerke in 1935.
[2] After the Second World War, Oestrich was captured and interrogated for a long time on technical issues.
[3] Together with other former BMW employees, such as Hans-Georg Münzberg, August Wilhelm Quick and Otto David, he accepted a five-year contract with the French Ministry of Aviation.
He founded Atar (Atelier technique aéronautique de Rickenbach) in 1946 and headed this development group of 120 employees.
In 1948 he acquired French citizenship and in 1950 he rose to technical director of Snecma in Villaroche, where the developments of the BMW 003 engine were being monitored.