Figures from the UK Civil Aviation Authority (CAA) suggest that traffic on the Shannon to London Heathrow route has been static for the last seven years.
According to a report in the current issue of Irish Air Letter, about 320,000 passengers per annum have travelled with Aer Lingus on the Shannon to Heathrow route between 1999 and 2006, which the journal describes as a "relatively low load factor of 71 per cent".
Referring to the proposed Belfast to Heathrow route, it says that BMI - British Midland - with 54 services a week, will offer the main competition for Aer Lingus.
And the aviation journal says Aer Lingus will face significant competition on its other Belfast routes, with the exception of the proposed Budapest service.
The journal notes that Aer Lingus will be competing directly with EasyJet on the Amsterdam, Rome, Geneva and Faro routes.
Low-cost airline EasyJet has just announced the launch of a Belfast to Barcelona service, which will compete with Aer Lingus, while another low-cost carrier, Jet2, already serves Malaga from Belfast.
It is likely to be several weeks at least before a decision is made on whether Dublin-based airline CityJet will launch routes from Shannon to London City and Charles de Gaulle (CDG) in Paris.
The Minister for Transport, Noel Dempsey, held talks with the airline, a wholly-owned subsidiary of Air France, at the weekend.
