New-generation turbofans powering Airbus A320neo-family jets and Boeing’s 737 Max are simply not as durable as the engines they replace.

That is according to AerCap chief executive Aengus Kelly, who on 8 May delved into an issue that has driven up maintenance demand and left airlines scrambling to keep jets flying amid a shortage of available maintenance slots.

Speaking during an AerCap investor day, Kelly calls the new-generation powerplants “engineering marvels”, but notes their improved efficiency has come at a price.

“They are not as durable… They break down more often. They are strained to the engineering maximum,” Kelly says during the event in New York. “They do not last as long in service, so they have to go to the shop, an MRO facility, to be repaired.”

Due to such issues, “demand for old aircraft is increasing all the time,” he adds.

PW1100G on A320neo.

Source: Airbus

Kelly does not mention specific engine types, but his comments came the day Irish lessor AerCap disclosed reaching an agreement to acquire 150 CFM International Leap turbofans as spares.

Leaps, which power 737 Max and are one of two A320neo-family engine options, have suffered durability issues since their introduction, as have Pratt & Whitney’s competing PW1100G – the other A320neo engine option. AerCap has both powerplants in its fleet.

An ongoing PW1100G durability issue has forced airlines globally to ground hundreds of Airbus jets for early inspections and replacement of potentially defective metallic components. P&W says the issue results from errors during a manufacturing process using powder metal.

PW1100Gs have suffered other, unrelated durability issues in recent years, some of which persist, aerospace consultant Jonathan Berger with Alton Aviation Consultancy said in April.

Meanwhile, CFM co-owner GE Aerospace is working to address Leap durability issues it says primarily have affected engines operating in dusty regions.

GE is introducing more-resilient blades and a new “reverse bleed-air system that provides cooling air after engine shutdown, thus mitigating the coking of unburned fuel in the nozzle”, it has said.

Experts attribute the problems, to a large degree, to the hotter temperatures and higher pressures at which the new engines operate – qualities helping make them 15-20% more efficient than earlier turbofans like CFM56-5Bs and International Aero Engines V2500s.

Engineers have given the new engines advanced materials intended to better withstand the extreme conditions, and devised complex features that divert air to cool components. Still, some parts are proving subject to early failure.

“These engines are running, you know, about 400 degrees hotter than their predecessors, and their pressures are 50% higher,” analyst Kevin Michaels with AeroDynamic Advisory said in February. “So, when you get into dirty air, you clog passages, you melt things that didn’t melt before in V2500, CFM56-5Bs.