Other budget airlines have ditched reclining seats in recent years, but according to industry experts long-haul carriers are unlikely to follow suit.
A survey for CabinCrew.com said the majority of international cabin crew had witnessed a dispute between customers over reclining seats.
Psychologists said the anger provoked by seeing the passenger in front lowering their seat-back could lead to negative emotions including stress, anxiety and frustration, and ultimately cause 'air rage' incidents.
Luton-based Monarch, which flies to holiday destinations around Europe and the Mediterranean - its longest flight is to Egypt, five hours away - said six of its Airbuses had the new seats, with another 11 due to be upgraded by the end of the summer.
"Our new ergonomic seats have been designed with our customers' needs in the forefront of our minds," said Tim Williamson, director of customer experience and marketing.
The new non-reclining design gives our customers far more "living space" than traditional seats, without the fear of the person in front impinging on their personal space.'
The overhaul follows a poll last October by flight search website Skyscanner found nine in ten plane passengers would like to see reclining seats banned on short-haul flights, or restricted to set times. Monarch's new seats - inspired by those used in cars - have bungee-style storage, instead of pockets, said to better accommodate items such as water bottles, clothing and children's toys.
The slimline design also features a holder for tablet devices such as iPads, allowing customers to bring their own in-flight entertainment. Fixed seat-backs prevent the risk of the screen being moved as the passenger in front reclines.
Lightweight seats will save 562lb of fuel on a five-hour flight, equivalent to 1799lb of carbon dioxide.
Monarch has trailled prototypes over the past 11 months, but the updated version features extra padding in line with customer feedback.
Budget airline Ryanair scrapped reclining seats in 2003 and EasyJet followed suit four years later.
- Daily Mail