Does anyone have any idea what Pionair actually referred to
Dave's suggestion seems eminently correct, a play on the word "pioneer".
Few, if any, civil aircraft have given such long and sterling service as has this Douglas twin-engined series. It is fitting, therefore, that in the evening of this worthy machine's life, B.E.A. should have chosen to honour the type by naming its Pionair fleet after the great figures of British aviation. Thus the spirit of men like Sir John Alcock, Sir George Caley and Sir Sefton Brancker will travel with these aircraft as they enter yet another phase of a seemingly endless career.
https://www.flightglobal.com/pdfarch...0-%200107.html
Seeing as the mods were done by Scottish Aviation I wonder if the fact they used the name "Pioneer" as model designations for some of their aircraft could have had some influence. There was the single engine "Pioneer" and the "Twin Pioneer". Who dreamt up the name "Pionair", Scottish or BEA?