In the face of the costly structural changes required to maximise the benefit of a new powerplant, Boeing and Embraer have cooled to the idea of re-engining their respective workhorse jetliners.

With year-end decisions to be made by Airbus, Boeing and Embraer on the future of the A320, 737 and E-Jet programmes, only Airbus remains bullish on the prospect of offering a new engine option for its A320 family.

Boeing Commercial Airplanes chief executive Jim Albaugh says the airframer is looking to a "737 Next Generation Plus" to bridge the gap between today's 737NG and a replacement aircraft in the 2020s.

Insiders familiar with Albaugh's remarks - made in a 7 September internal discussion broadcast companywide - say the 737NG+ concept so far lacks specifics, but the goal is to keep the 737 on an equal footing with an A320 NEO (new engine option) without incorporating a new engine.

Meanwhile, Embraer director Carlos Eduardo Camargo says initial evaluations of a new engine for its 70- to 100-seat E-170/190 family suggest the fuel burn benefits of an engine upgrade may not match the cost of major modifications to the wings, pylons and landing gear needed to accommodate the larger fan of a Pratt & Whitney PW1000G or CFM Leap-X.

"We really have to see how it works. We have engineers simulating [different configurations] working with the [engine] producers, we obviously do not have a final decision or a final idea on that," says Camargo.

Camargo notes that key competitors - Bombardier CS100, Mitsubishi Regional Jet and Sukhoi Superjet - could top E-Jet performance by 8-12%. "We have to learn to beat that," he says.

Embraer may, he says, look to aerodynamic modifications to the wings, including Boeing 787-style raked wingtips in place of today's blended winglet to improve efficiency while maintaining the current GE CF34-8E/10E engines.

Airbus and the engine makers contend a PW1000G or CFM Leap-X powered A320 NEO would yield a net fuel burn benefit of 13-14%, after factoring in the 1-2% lost to airframe modifications. Boeing's Albaugh counters that the NEO would only offer a 3-4% improvement over today's A320 - which he says would only bring the European narrowbody in line with today's 737.

This ongoing debate underscores the fact that the benefits of any of the airframers' options - over making no changes to current product - are far from obvious.

Airbus says it would charge a $7-8 million price premium for an NEO, which it calculates as half the net present value of the fuel savings a customer would make compared with operating a current standard A320.

The gamble for an A320 NEO customer would thus pay off even if fuel prices rise significantly beyond Airbus’s forecast – but could be a losing proposition if prices fall.

Net-benefit calculations are murky for Boeing and Embraer customers, as the purchase price of a 737NG+ or E-Jet upgrade remain unknowns.

Pratt & Whitney says: "We could achieve fuel burn improvement with a GTF with an installation on today's E-190 with no changes. However, to optimise performance and achieve double-digit benefits for a re-engining, an engine with a larger fan is required.

"We agree that Embraer would have to make modifications to its aircraft, including changes to the landing gear, to accommodate an engine with a larger fan. We have been working closely with Embraer to study optimised installations to achieve the greatest benefits."

Source: Flight International