Hi Shed-on-a-Pole and Roll to the end,
I think you're both probably right: Yes, LPL and MAN have their own catchment areas, but when you're dealing with a small market (e.g. NOC) there's evidence that the two airports affect each other.
As you can see from the CAA data below, bmibaby's MAN-NOC service has been losing passengers ever since Ryanair launched the LPL service in 2007. The LBA 'pincer movement' undoubtedly added to the pain last year. Loads on MAN-NOC have also been declining, from an average of 77% in 2008 to 64% last year. Loads on NOC-LPL have been consistently awful, averaging 52% last year. I doubt that yields have been spectacular for either carrier.
If Ryanair are going to do NOC from both LPL and MAN, they will almost certainly need to adjust their frequencies from LPL. I'm sure that daily B738 services are not sustainable from both. How big is the market at ticket prices that are sustainable? Maybe 100,000 per year from both MAN and LPL? In which case I would suggest that a total of 7 or 8 services a week from both is what we will end up with. Come back to me on that one next year
The same problem will occur if they try LDY from both LPL and MAN.
A similar situation exists on NOC to BHX / EMA, where growth to EMA has been at the expense of BHX. However, so far bmibaby are holding out.
