For a description of the format and data included in
Production Tables, see here.
Produced Variants
Type 521
Two seat fighter trainer utilizing
components from various Type 504 models, including Type 504A mainplanes of reduced span. 110 h.p. Clerget powerplant.
Type
521A
As Type 521 with three bay mainplanes of larger span.
25 Avro
Type 521 aircraft were ordered, although it appears only 7520 was completed [2]. It is likely that all those airframes built
were converted to 504Es.
Production References
Avro
Aircraft Since 1908, A.J. Jackson (Putnam, 1965)