The first planes to come in for maintenance work in July 1940 were Finnish Viima training aircraft. The distribution of work between the two plane factories in Kuorevesi was that the Karhumäki factory was mainly in charge of repairing basic and more advanced training planes, and the Valtion Lentokonetehdas factory was in charge of repairing communication and war planes and assembly.

The licensed fabrication of Dutch Fokker D.21 fighters began in Tampere in the year 1939. The following year an order for them was placed at Valtion Lentokonetehdas. Kuorevesi factory began with the serial fabrication of 50 fighters. The first aircraft made in Kuorevesi, the FR-118, took off on its test flight on 29 October 1940 and was piloted by Erkki Itävuori. The Fokker D.21 was a one-seat plane of mixed construction, made of steel, aluminum, wood and fabric.

In the last year of war, the importance of the Kuorevesi factory became immense as most of the repair work on the two most powerful planes, the Messerschmitt BF-109 fighter and the Junkers 88 bomber, was done there.

The work of the Air Force test flight section began in Kuorevesi in 1940, when ten Focke-Wulf Stieglitz planes were brought from Germany to Kuortane. Test flying was important also in peace time, because flight training caused a lot of damage to the aircraft and that in turn meant repair work for the industry. Information about repaired war booty planes was gathered through test flights, as there were no manuals available.