Three elderly couples were on the vintage biplane that went missing in Queensland.
The plane, believed to be a restored Dragon and piloted by owner Des Porter, went missing near the town of Kilcoy this afternoon.
Police say the aircraft was due to return to Caboolture Airport around 2.15pm (AEST).
The six were part of a large number of aviation enthusiasts who descended on the small town of Monto, 180km west of Bundaberg, for a weekend airshow.
An air and land search west of the Imbil area is under way.