"Can anyone enlighten me as to why there is such a relatively high frequency between Aberdeen and Norwich? Both cities are pretty small and haven't a huge population in their hinterlands either."
Oil & Gas platforms in the North sea is my guess, the Humberside-Aberdeen route also serves this sector for the rough field platforms just off the mouth of the River Humber.
This route alone is serviced by both Gamma Aviation and Eastern
Apart from Eastern and newcommer BMI regional, who else operates the Norwich-Aberdden route?