The Auster D.4 was a two-seat British light aircraft, a development of the Auster Arrow with a horizontally opposed Lycoming engine, which originated from a Portuguese Air Force requirement for a liaison/training aircraft.

[1] Six were built by Auster Aircraft at their Rearsby, Leicestershire, factory, of which five went to Portugal, and nine more were built under licence in Portugal by the Oficinas Gerais de Material Aeronáutico OGMA from sets of components built by Auster and shipped from Rearsby.

[1] Most D4 aircraft were operated in Portugal by government sponsored groups.

One example is still active (2018) owned by a UK-based private pilot owner.

Data from British Civil Aircraft since 1919: Volume I.