Stephen Udvar-Hazy has advised Boeing and Airbus to forget about upgrading their most popular planes with new engines.

Udvar-Hazy, founder of the world's largest aircraft leasing company, International Lease Finance Corp., and now the president of Air Lease Corp., said the benefits of fitting the Boeing 737 and the Airbus A320 family of single-aisle jets is too little to justify the expense, reported Bloomberg News.

Speaking in Munich, Udvar-Hazy said the re-engined planes would be too expensive and too heavy to compensate for the fuel they would save. Both Boeing and Airbus are considering whether to put new engines on those best-selling planes to compete with new jets from Canadian and Chinese manufacturers.

Airbus seems closer to giving the go-ahead to the re-engine programme, while Boeing reportedly favors making minor aerodynamic improvements to its 737 now and building an all-new 737-sized jet in a few years.

The re-engining programmes would be considerably less expensive and technologically complex than the all-new airplane option, but would yield far less in terms of improved operating costs.

Airbus claims the new engines would trim fuel consumption by 15%. Udvar-Hazy said the higher purchase price of the re-engined planes and the costs of airlines' maintaining a different aircraft in their fleets would greatly reduce that advantage.

Udvar-Hazy has a strong influence in the airplane business. When he publicly declared that Airbus' plans to upgrade its A-330 jet to compete with Boeing's all-new 787 was too little, Airbus scrapped those plans and decided to build an all-new plane of its own, the A-350XWB.