Avro 504N - European Users

Th Avro 504N was an improved version of the Avro 504K, with a new engine and some other aerodynamical changes which consisted on a new undercarriage, new wings, a new engine and the removal of the skid. Some internal improvements were also made like the inclusion a direct gravity feed for gas.

It was used by many European countries as it became their standard trainer airplane and it was license built in Belgium by SABCA during the late 1920s until mid-1930s, and in Greece by the Kratiko Ergostasio Aeroplanon (State Aircraft Factory) from 1934 until 1935.

It was powered by either a 150hp or 180hp Armstrong Siddeley Lynx IV engine.

• Belgium: It was the backbone of their trainer squadrons during the 1930s decade. Some of them were still in service when Germany invaded Belgium in May 1940.
• Denmark: The 504N was also the main trainer of the Royal Danish Air Corps during the late 1920s until the mid 1930s. It's worth to mention that these airplanes were equipped with a cowling in the back seat in order for the student to learn how to "blind pilotage".
• Greece: The Greeks ordered some 504N in 1925. 
• Sweden: In December 1925 the Swedish Army Aviation Company ordered five 504N which were delivered in April 1926. They served under the denomination of Sk-3 and Sk-3A in the Flying School at Ljungbyhed. Surprinsingly, they served only until 1928 as they couldn't cope wheel with the harsh cold Swedish weather.
• United Kingdom: The 504N replaced the 504K as the main RAF trainer during the 1920s.

Sources:

1. https://en.wikipedia.org/wiki/Avro_504

2. http://www.natureandtech.com/?cat=109

3. http://forum.valka.cz/topic/view/108754

4. http://greek-war-equipment.blogspot.com.es/2010/10/1920-1936-avro-504.html

5. http://www.avrosys.nu/aircraft/Skol/403sk3/403Sk3.htm

6. http://aviadejavu.ru/Site/Crafts/Craft33477.htm (translated)