Passengers board a Ryanair flightBloomberg

Ryanair, the famously no frills Irish airline, is being investigated this week by an air safety watchdog for charging passengers sitting next to emergency an extra $15.

The emergency ares seats are popular with some travelers for their additional leg room, a fact that Ryanair noticed before it decided to charge passengers for the privilege of sitting there.

Standard operating procedure asks that fliers occupying those seats must follow safety directions and be able to open the emergency doors in the event of an emergency.

But acceding to a report in the Daily Telegraph this week some passengers refuse to pay the extra charge, which means that many Ryanair flights have taken off with those seats vacant.

When this happens passengers in the surrounding rows further away from the exit are asked to familiarize themselves with the emergency evacuation procedure.

But some of those passengers have reportedly claimed they were unable to understand the safety instructions on how to open the emergency doors, since they were not sitting next to the exit.

In response to the growing controversy the Irish Aviation Authority (IAA) launched an investigation into the issue, and the Civil Aviation Authority and the British Airline Pilots Association (BALPA) also expressed their concerns.

'Our guidance to UK-registered airlines is that whoever is sitting next to the emergency exit must be briefed about what to do,' a spokesman for the CAA told the Telegraph. 'If that person says they are not willing to do it, then someone else must be found who is happy with that role.'

'It's an important task. It's not easy to open the doors and they must be physically strong enough to throw them from the plane.'

in response to the recent investigation a spokesman for Ryanair said the company does not believe the issue will be a problem, but said the airline would continue to cooperate with the IAA.

'Ryanair complies with all mandatory safety directives. All passengers are provided with the same safety and evacuation information.'

Ryanair is not the only low cost flier to add the charge, a number of other airlines registered in Britain also ask passengers to pay extra to sit next to the emergency exit.