Emeritus
Yes I too thought that ABR would hold the record but the numbers don't support it.
Technically ABR did not come into Ansett ownership until 21 October 1957 when Ansett took-over ANA. ABR operated its last commercial service on 27 December 1972 although the aircraft remained in Ansett ownership right up until close of business in 2001. That's 15 years in service. If you add its ANA service that brings it up to 34 years.
F.27 VH-FNQ was in service from 1966 to 2001 which is 35 years, all in Ansett ownership. The only other contender that I can think of is Sandringham VH-BRC but that was in service for a mere 22 years.
It surprised me too.
Rgds