Hello!
Estonian-manned Sonderstaffel Buschmann started patrolling Gulf of Finland with PTO-4 planes from March 11th, 1942. This was signalled also to Finnish Air Force to avoid "friendly fire" incidents.
PTO-4 was Estonian built and designed two-seater monoplane trainer. See:
http://www.hot.ee/relvaleht/pto-4.jpg
http://www.hot.ee/relvaleht/pto-4_1.jpg
The photos of PTO-4 SB+AD linked above are very likely taken early spring 1942.
EDIT direct link to the first photo does not seem to work. When the page appears click on the left frame text "lennusalga lennukid" (planes of the
lennusalk)
Regards,
Kari
PS I think most of Estonians would be insulted if you called them "Eastern" people. Culturally Estonia is part of West, predominantly influenced by Germans which were for centuries the ruling class.