The Aero A.42 was a Czechoslovak bomber aircraft of 1929 that was only ever produced in prototype form. For its day, it was an advanced design, with a sleek monoplane configuration. However, the Czechoslovak Air Force was not satisfied with it for a number of reasons. In particular, the aircraft's take-off and landing runs were felt to be excessively long, and crew complained about the cramped cabin. The air force suggested a set of modifications to Aero, including replacing the wooden wing with a metal one, but Aero discontinued development.
On 20 September 1930, one of the two prototypes set international speed records of over a closed circuit, carrying payloads of and .
One prototype was used by the Czechoslovak Air Force until 1938, then by the Slovak Air Force. Probably it was scrapped in 1940.
The A.42 was a single-engined high-wing cantilever monoplane with fixed landing gear.