Would Ryanair do trans-atlantic? - Perhaps it already does.

Mr Cawley acknowledged there is "a small market" for a trans-Atlantic LCC but thought this would be too much of a distraction for Ryanair. "At one stage in our history we grew by 9 or 10m passengers in a year. If you were 9 or 10m passengers trans-Atlantic you would be the biggest gorilla on the market. And then what would you do the next year?"

Often overlooked in the trans-Atlantic discussion is the opportunity for a US carrier to enter, such as the independent JetBlue. But JetBlue SVP marketing Marty St. George was not interested at the time: "If you look at the fares from New York to Europe, six months out of the year it looks like the LCC flies it. There are regularly fares that are in the two digit dollars."

JetBlue, he said, likes to see "markets with high fares we can stimulate. For much of the year it's going to be tough to stimulate the trans-Atlantic marketplace."

Aer Lingus then-CCO (now CEO) Stephen Kavanagh quipped Ryanair already has a foot in low-fare trans-Atlantic operations: "Ryanair, as Aer Lingus' largest shareholder, does have a rather large investment in a very compelling and efficient trans-Atlantic carrier."

Ryanair potentially selling its Aer Lingus stake to IAG would lose its foothold in Aer Lingus. Under IAG, Aer Lingus could gain more efficiencies and further reduce its cost base.

Since 2007, 19 airlines have launched (or plan to launch in 2015) scheduled widebody long-haul service, and maintain the operation today. Twelve, or two-thirds, of the airlines are LCCs.

Norwegian operates nine of the 10 longest widebody LCC routes in 2Q2015 - perhaps unsurprising given it has the longest average sector length (7,450km). This is more than twice the average sector length for Cebu Pacific and Scoot. In fact, during 2Q2015, Norwegian operates 21 widebody LCC routes, meaning about half of them are in the top 10. The only non-Norwegian route of the 10 longest is Jetstar's Melbourne-Honolulu service.

Widebody LCCs have short-haul flights for varying reasons. Scoot operates Singapore-Bangkok (1,437km) as the flight makes efficient use of aircraft downtime and provides connecting opportunities beyond Scoot's relatively small and mature home market of Singapore. Scoot also has tapped into fifth freedom opportunities, such as Taipei to Tokyo (2,182km) and Seoul (1,460km).

The shortest average sector length of main widebody LCCs is Cebu Pacific with an average sector length of 3,256km. Cebu operates a number of sectors over 6,900km, but the average is brought down by two domestic routes: a two to three daily return service between Manila and Davao (962km) and about a daily service between Manila and Cebu (565km). Both of these routes are Cebu's largest by seats and frequency in the domestic market. Given frequency saturation and Manila's congestion, up-gauging is logical and makes use of aircraft downtime.

Jetstar also operates a number of domestic sectors with its widebody fleet, mostly to rotate the aircraft between bases and pick up passengers in multiple cities.

Short-haul narrowbody LCCs sometimes face the task of flying "hand-me-down" routes, those that a full-service parent no longer wants to serve. For the widebody LCC sector, some carriers (AirAsia X, Azul) have no full-service parent to answer to so the topic is not applicable. Jetstar in 2014 launched a route (Melbourne-Tokyo) that parent Qantas used to serve - but some years ago.

Eurowings was announced with the objective to help restore the presence of part-owner Lufthansa. Of Eurowings' initial intercontinental routes, Bangkok and Dubai are already served by Lufthansa - but not from Cologne where Eurowings will launch from. However, Lufthansa has decreased Bangkok and Dubai capacity over the years, perhaps indicating Lufthansa will try to restore its group presence via a different operating platform and departure city. Other Eurowings destinations - Phuket, Punta Cana and Varadero - are entirely new to the modern Lufthansa.

Singapore Airlines has cut some long-haul points and offered - but not forced them - to its LCC Scoot, which declined to pick them up. Jin Air, the first and so far only North Asian-based long-haul LCC, is mooted to expand the network of Korean Air, which indirectly owns Jin Air, and could take over Korean Air routes.

Air Canada rouge has been directly handed-off routes from Air Canada mainline (such as Toronto-Lima) but rouge has also been used to restore the group's presence: Air Canada suspended Osaka Kansai service in 2008 but rouge will pick up the destination in 2015. rouge has also opened up entirely new points in lower yielding markets for Air Canada (such as Lisbon and Nice).