[1] Like the Aero A.100 upon which it was based, the A.101 was a single-engined biplane of mixed metal and wood construction, with a fixed conventional landing gear.

[7] In March 1935, the Czechoslovak Ministry of Defence issued a requirement for a revised version of the A.101, the Aero Ab.101, to be powered by a Hispano-Suiza 12Ydrs engine, which promised improved performance.

[8] The Ab.101 was longer than the A.101, in order to maintain the aircraft's centre of gravity with the lighter Hispano-Suiza engine,[7] while maximum bombload increased to 1100 kg.

[5] During 1936, two A.101s were destroyed in accidents, both as a result of engine failures, while the aircraft suffered from degradation of the plywood covering the wing leading edges, which required repair by Aero.

[6] On 23 January 1937, a contract was signed to sell the Spanish Republic all 28 remaining A-101s, together with 24 Letov Š-231 fighters and spare parts, using Estonia as an intermediary.

The delay meant that the presence of the Aeros and their destination was well known in Gdynia before Hordena departed port, and a Nationalist agent warned that the freighter was carrying arms for the Republicans.

[13][14][15][c] The captured aircraft entered service with the Spanish Nationalist Air Force, where they were known as Oca (Goose) or Praga (after the engine manufacturer).

[8] The Nationalist A.101s took part in the Battle of Brunete in July 1937,[18] and continued to be heavily used until the end of the war, although they were obsolete, with nine A.101s lost due to enemy action or acctidents.

The 5th Air Regiment's Ab-101s were deployed to airfields in western Slovakia and southern Moravia to guard against a potential attack from Hungary, as they were not considered adequate to face the German Luftwaffe.

It was planned to phase out the type following replacement by license-built B.71 bombers (the Czechoslovak designation for the Soviet Tupolev SB), but before this could happen, Germany occupied Bohemia and Moravia on 15 March 1939.