(Reuters) – Airbus SE AIR.PA and Boeing Co BA.N are expected to turn to hybrid electric technology when they develop the next generation of airplanes because of limits on improving current engines, the head of a major aircraft lessor said on Thursday.

Airbus is already working hard on a hybrid solution but Boeing is likely to be more cautious about making a major investment in a new program given its challenges with the return of the 737 MAX and certification of the 777X, Air Lease Corp AL.N Chief Executive Steven Udvar-Hazy said at the Skift Aviation Forum.

“I have serious doubts that either Boeing or Airbus can design an all new airplane using current aerodynamic engine technologies that can have a meaningful – let’s call it double-digit advantage over what we already have,” he said in reference to fuel efficiency. “So what I see evolving is more of a hybrid.”

Udvar-Hazy said hybrid engines would allow for a lighter aircraft weight, as well as a technology transition rather than a step change.

“Almost like we didn’t go from all piston engine and diesel cars to all electric cars,” he said. “There’s that transition with hybrids that have a smaller gasoline engine and then an electric augmentation engine, like the Prius for the example.”

Airbus said last year it was considering producing a hybrid plane by 2035 as it strives for a low-emission aircraft, while Rolls-Royce Holdings PLC RR.L said in March it expected hybrid planes carrying around 100 people to be flying commercially by 2029.

Boeing did not respond immediately to a request for comment.

Boeing’s director of environmental strategy Sean Newsum said in January that scaling up hybrid technology to a 737-sized plane could take decades, though hybrid-powered regional planes could enter service in the 2030s, according to a FlightGlobal report.