By Tim Hepher

PARIS Airlines could face shortages of planes, engines and parts for several years as they try to meet a strong rebound in travel demand, the head of aircraft leasing giant AerCap told Reuters.

Aerospace firms have predicted supply chain problems for at least 18 months as airlines clamour for jet deliveries to meet the new demand. But AerCap Chief Executive Aengus Kelly predicted pressure well into the second half of the decade.

"The most important point in the longer term is the supply constraint that will last for many years," Kelly said in an interview, adding this would spread beyond production lines and into already congested repair or "MRO" facilities.

Boeing CEO Dave Calhoun last week predicted supply problems for a "very long time". When asked at the Qatar Economic Forum to define such a period, he drew attention to the company's order backlog stretching over the next five to six years.

"We feel very much the same, be it airframe issues, engine issues, MRO capability, both on the airframe and the engines," Kelly said, referring to Calhoun's mention of five years.

Calhoun also said it would take until end-2024 before jetmakers were able to sharply boost aircraft output. Delivery delays have been blamed for part of the capacity squeeze.

Kelly said the shortage of supplies had also been compounded by the more frequent repair visits required by the latest engines.

"The new assets have great fuel burn and wonderful engineering ... but they are not as durable as the previous assets, such as the (Boeing) 737, the (Airbus) A320."

"So they come off wing faster and there's more time on the ground. And I just don't see that changing for years and years to come."

Demand will also remain strong for the "foreseeable future," he said.

"I see strong demand now on a global basis. No doubt over the next few years, there will be regions in the world that will have their ups and downs and that may affect individual carriers."

The International Air Transport Association said ahead of a global summit of airlines in Istanbul on June 4-6 that global passenger traffic had increased by 46% year-on-year in April.

One potential positive from the supply squeeze is that airlines may be less able to respond to the spike in demand by installing too much capacity as they have tended to do in the past, creating an overhang when the market turns lower.

"I strongly believe that the supply-side constraint will severely dampen the impact of any downturn in demand," Kelly said.

(Reporting by Tim Hepher; editing by Barbara Lewis)