Adds context, background, Ryanair CEO quote

By Tim Hepher

PARIS, Feb 12 (Reuters) - French-US jet engine maker CFM is studying a more conventional "advanced ducted" engine design alongside its preferred option for a radical open-fan concept for future jets, as the industry debates fuel-savings and lower emissions, industry sources said.

The venture co-owned by GE Aerospace GE.N and France's Safran SAF.PA has been championing an open-rotor engine, featuring a large exposed fan instead of a traditional casing, as the most efficient and environmentally friendly architecture for the next series of Airbus AIR.PA and Boeing BA.N jets.

It says this would generate fuel and emissions savings of 20% under a widely publicised research programme called RISE.

But it is also looking in a more structured way than previously reported at a design where the fan would be contained inside a shell similar to casings on current engines. Experts say such designs save less fuel but can be more adaptable.

SAFRAN CODE NAME REVEALS ALTERNATIVE DESIGN

The choice of technologies has potential implications not only for the efficiency of aircraft entering service around 2040, but the commercial strategies of Airbus and Boeing.

The project to study the alternative architecture came to light in a Safran employee's job description seen by Reuters.

The employee's duties include work on future projects including the "Open Fan" and a separate, unpublicised project that Safran has internally named "Advanced Ducted-Large" or ADL.

Three industry sources confirmed that CFM is working on "advanced ducted" architecture under RISE, which targets a cluster of technologies ahead of any specific engine design.

Safran and GE both declined to comment.

CFM and its two shareholders have consistently said they are ready to provide whatever engines planemakers want and have never ruled out choosing a more conventional design, even as they tout the benefits of the open-bladed architecture.

But the emergence of a separate code name inside one of CFM's shareholders is the first tangible sign that the alternative engine design is being taken seriously enough to warrant standalone attention.

INDUSTRY SPLIT ON NEW TECHNOLOGY

Although some years away, designs for the next round of passenger jets and engines are already a topic of debate because of maintenance bottlenecks that have left dozens of jets idle.

Airlines have been bruised by higher-than-expected wear and tear on the most recent engines, which have eaten up part of the cost savings from a 15% drop in fuel burn.

Airbus broadly supports the open fan concept while Boeing - backed by CFM's main rival Pratt & Whitney RTX.N as well as Britain's Rolls-Royce RR.L - is less convinced.

Mixing incompatible designs would make it harder to offer a choice to airlines, so final decisions are expected to shape decades-long partnerships and affect the way airplanes are designed and sold.

Influential customers are also divided, with leasing giant AerCap AER.N urging engine makers to be wary of over-emphasising fuel burn at the expense of durability.

The CEO of major Boeing and CFM customer Ryanair RYA.I wants engine makers to go all out for fuel savings.

"I would take the fuel savings all day long. My biggest cost is fuel," CEO Michael O'Leary told Reuters.

(Reporting by Tim Hepher; Editing by Bernadette Baum)

((tim.hepher@thomsonreuters.com; +33 1 49 49 54 52; Reuters Messaging: tim.hepher.thomsonreuters@reuters.net))