Airbus SAS and Boeing Co. said they are considering whether to upgrade their most popular jets with different engines to cut fuel consumption and buy time to design all-new successors.

“Is it feasible to re-engine the 737?” Boeing marketing chief Randy Tinseth told visitors of an aerospace conference in Dubrovnik, Croatia, that ended yesterday. “The answer is yes. It’s a question of what the customer needs, and what makes sense from an investment point of view.”

Chicago-based Boeing and Airbus, based in Toulouse, France, have a combined 4,500 back orders for their best-selling Airbus 320s and Boeing 737s, and successors won’t be available before 2020. Clients such as Qatar Airways Ltd. are pressuring Airbus and Boeing to rework the jets as airlines consider alternatives from rivals including Bombardier Inc.

Airbus and Boeing are fighting to defend their dominance in the single-aisle jet market because the models finance development of larger planes. Engine makers including General Electric Co. and Pratt & Whitney say they could make a turbofan engine available as soon as 2016 that would cut fuel consumption and noise. Redesigning planes to accommodate the engine would cost less than $1 billion, compared with $10 billion to create an all-new model.

Industry Workhorse

Single-aisle jets, with 100 to 200 seats, have been the industry’s workhorses for decades. Boeing and Airbus combined have delivered more than 9,000 narrow-body planes since the first Boeing 737 hit the market in 1967. Airbus may not offer a successor to the A320 until 2024, sales chief John Leah said last month. Boeing has earmarked its next model for 2020.

“Anything’s possible,” said Andrew Gordon, the Airbus director of market analysis, in an interview at the Dubrovnik conference. “We have to think about what’s best for our customers, and what’s best for the environment. Timing will be important.”

A plane with a reworked engine typically requires modifications to the pylon that connects wing and engine, as well as to air ducts, fuel lines, cabling, landing gear and hydraulics. Boeing may struggle to accommodate a different engine under its 737 because the wings sit lower to the ground than those of the A320.

Lower Costs

Designing a new model occupies thousands of engineers for several years. Upgrading an existing model with a new engine would instead function “partly as a band-aid solution to buy some more time,” said Steven Udvar-Hazy, chief executive of International Lease Finance Corp., the world’s largest aircraft lessor.

To be sure, re-fitting a plane has its risks. A fleet that mixes planes with traditional and new engines creates additional costs for parts and mechanics. A revamped version may be financially attractive only for a decade, until the two companies bring out their all-new models, Udvar-Hazy said.

Airbus flight tested Pratt & Whitney’s so-called geared turbofan engine last year to evaluate the technology. Pratt, a unit of United Technologies Corp., says the model offers about a 15 percent fuel advantage over current engines. It so far only offers it for the Bombardier C-Series model and Mitsubishi Corp.’s regional jet, neither of which fly commercially yet. It supplies standard engines to the A320 family through a venture it leads with Rolls-Royce Group Plc.

‘Significant Benefit’

“We believe our technology would offer significant benefit for re-engined A320 and 737 aircraft,” said Edward Kokoszka, general manager for Pratt’s commercial engines in Europe, who also spoke at the Dubrovnik conference of the International Society of Transport Aircraft Trading, or ISTAT.

Boeing’s 737 model uses CFM56 engines by CFM International, GE’s joint venture with Safran SA of France. CFM says it could provide a more fuel-efficient engine in 2015 or 2016. Airbus’s A320s use the CFM56 or the V2500 by International Aero Engines, a venture led by Pratt & Whitney and Rolls-Royce, each of which owns about a third.

Oil prices are another critical component of the equation. At about $70 a barrel, the savings from new engines’ increased fuel efficiency probably won’t be enough to offset the greater costs from having a mixed fleet of engines.

If oil returns to levels of $100 a barrel, the 15 percent to 20 percent fuel-efficiency gains would more than balance out additional costs of having two different engine types.