Eight hours on the smallest aircraft might not appeal but cheaper fares and new routes might.

The smallest aircraft made by Boeing and Airbus Group are about to find a new role operating trans-Atlantic routes that were previously the preserve of some of the world's biggest planes.

The re-engined 737 Max and A320neo jets offer a 15 per cent fuel saving meant to cut costs on the shortest inter-city services.

At the same time the revamp has added about 800 kilometres to their range - just enough to allow the narrow-bodies to span the 4828km between the eastern US and Western Europe.

MATT MILLS MCKNIGHT A Boeing 737 MAX plane at the Boeing plant in Renton, Washington.

While eight hours on a 40-metre plane with three toilets and one gangway might not immediately appeal to travellers used to the spacious cabins of an Airbus A380, airlines say the smaller jets will open up direct routes that wouldn't otherwise be viable.

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That would do away with the need to switch between flights at a busy hub.

REGIS DUVIGNAU/REUTERS Flight test engineers taxi the Airbus A320neo (New Engine Option) after its first flight in Colomiers near Toulouse, in 2014 file photo.

At the same time people can look forward to competitive fares as carriers seek out smaller airports where access charges are lower.

Norwegian Air Shuttle, JetBlue Airways and Portugal's TAP are among airlines buying the jets for trans-Atlantic routes, with NAS set to lead the way when it becomes one of the first carriers to get Boeing's Max 8 next year.

Its initial flights may link Edinburgh, Birmingham in England and Cork and Shannon in Ireland to smaller airports in New England and the New York area.

REGIS DUVIGNAU/REUTERS Employees work during the delivery of the first series-production LEAP-1A propulsion systems by Aircelle for the A320neo aircraft Airbus family at the Aircelle plant in France.

"The Max is very competitive," Norwegian Air Chief Executive Officer Bjorn Kjos said.

"It has huge potential from the smaller cities along the Atlantic coast. But you can't go into New York as you do with wide-bodies. You must target airports with a totally different cost structure."

Boeing's 757, the world's longest single-aisle airliner with around 200 seats and a range in excess of 6400km, has been plying the Atlantic for years, with companies including United Continental Holdings Inc. still deploying the model on routes such as Newark, New Jersey, to Birmingham, England.

Production ceased in 2004, however, leaving those 757s still flying in the twilight of their lives and with fuel consumption way in excess of modern jets.

The 737 and A320, by contrast, were designed for much shorter flights, with the original 737-100 seating just 85 people and limited to trips of about 1900km. While ranges have increased, the 5400km reach of the 737-800 and -900 is insufficient for fully laden operations on trans-Atlantic routes where jets must carry enough reserve fuel to fly about 500 miles in an emergency.

A handful of carriers operate services at reduced capacity, which cuts the weight of a plane and increases its range, with SAS serving Boston from Copenhagen using an 86-seat 737-700 and British Airways connecting London City airport and New York with an Airbus A318 carrying just 32 passengers.

The only current trans-Atlantic 737 or A320 services with a near-normal load are flown by Canada's WestJet Airlines Ltd. and link St. John's, Newfoundland, with Dublin -- distance 3200km miles -- and Halifax, Nova Scotia, with Glasgow in Scotland. The 737-700s used have 136 seats.

The UK and Irish routes planned for Norwegian's 189-seat Max 8s will span about 4800km. Subsequent flights could serve Stavanger, Trondheim and Bergen in Norway and Aalborg in Denmark, though they'll likely involve a long-range version of Airbus's A321neo known as the LR and able to fly more than 6400km using extra fuel tanks, spokesman Lasse Sandaker-Nielsen said. Norwegian ordered 30 of the planes with 220 seats in a single class in July.

JetBlue and TAP also plan to deploy the model, which is due to be available from 2019. The US carrier has agreed to buy 30 A321neos with an option to take some as LR variants, saying it wants an aircraft with "trans-Atlantic range."

TAP has orders for 10 A321neoLRs, saying it could use them to serve Brazil and possibly the U.S. Its Lisbon base is about 5600km from both New York and Recife, the South American country's sixth-largest city.Ireland's Aer Lingus is also a likely operator of the A321neoLR across the Atlantic, Willie Walsh, CEO of parent company IAG SA, said in July, adding that the jet represents a "fantastic opportunity." It already flies 757s to locations including Hartford, Connecticut, typical of the cities smaller planes could serve.

With the LR emerging as a favored successor to the 757, Boeing is studying designs for a stretch of its biggest Max 9 - dubbed the Max 10 - that would offer much of the range and payload of the A321 and could be ready by the decade's end, or a more elaborate revamp using the larger engines developed for the Airbus jet. It's also working on a new family of mid-range aircraft that would debut about five years later, CEO Dennis Muilenburg said Wednesday.

Whatever the outcome, passengers seem certain to be making longer trips on the smallest class of jetliners in coming years.

"For the moment we haven't really got the planes out there," said Yan Derocles, an analyst at Oddo Securites in Paris. "But they're coming."