Joe Maloy, director of propulsion engineering for US Airways, reports that one of the most important concerns that airlines have about new-technology powerplants is “engine performance retention,” which, he says, relates mostly to any changes with fuel-burn and EGT margins. (He says that, at this time, US Airways has neither the 737 MAX nor A320NEO on order.)

“When you start seeing fuel-burn increases, that's a sign that the engine's performance is deteriorating faster than expected. That, and narrowing EGT margins, need to be mitigated by the maintenance service contract with the OEM,” Maloy explains. “Performance retention is a much bigger concern than the risk of an inflight shutdown with the new-technology engines coming along.”

For the NextGen Leap and PW1100G, the unanswered question is component durability, Maloy stresses.

“What drives an engine off-wing is any failure in the accessories or hardware that surround the engine, rather than the condition of the gas generator,” he says. “Both the CFM Leap and the Pratt & Whitney PW1100G are being advertised to achieve a 15% or better mission fuel burn, but pushing an airplane to do that means that the engine will operate at a higher speed and a higher internal temperature. Although the components should be able to withstand the higher temperatures, will they be able to do this over a significant period of time?”

Craig Harry, US Airways' supply-chain managing director, advises that as more new-technology engines are introduced, contractual flexibility in cost-per-hour maintenance plans will become even more important.

“When you deal with new technology, your knowledge of that engine, and the way it will perform, will be extremely limited at the start of the program, simply because there hasn't been any real experience with the engine,” Harry explains. “If the engine performs better than expected, adjustments in the cost per hour should be specified up front in the contract, rather than renegotiated during the life of the contract.”

The contracts also should guarantee availability of spare engines on a no-limit basis, he says.

“The performance and cost guarantees are the burden on the OEM,” Harry stresses.