Apologies if this has been said before or I'm stating the obvious, but BMI Regional operating Doncaster-Frankfurt would be for very different reasons to Jet2 flying Leeds-Doncaster.
A Doncaster-Frankfurt route would likely be a 37-seat or 49-seat aircraft (i.e. high costs per passenger) with a Lufthansa codeshare, to allow passengers from Doncaster to fly anywhere in the world on a single ticket via a 1-stop change in Frankfurt. BMI Regional do something similiar from other airports in Sweden, Belgium and Switzerland. Flights will likely be aimed more at business-centric passengers who value a high level of customer service / product quality. A simple DSA-FRA ticket is unlikely to be very cheap.
Jet2 flying Leeds-Dusseldorf is a 148-seat aircraft is about flying passengers point-to-point (i.e. no onward connections) between the UK and Germany. The area around Dusseldorf has a much higher population compared to the area around Frankfurt. With a large aircraft, costs per passenger are much lower and many more of the passengers are likely to be travelling for leisure purposes and more price conscious.
Last edited by davidjohnson6; 25th Oct 2015 at 15:31.