The head of one of the world's largest aircraft leasing companies issued a stark warning that Airbus and Boeing are building too many planes, with some recent blockbuster orders unlikely to be completed in full.

Airbus, a division of the European Aeronautic Defence & Space Co. EADS NV and Boeing are boosting output by around 40% over the next two years, citing demand from emerging markets and the need for developed-nation carriers to replace older planes. The world's two dominant aircraft makers also want to sell more aircraft to fund future programs after delays on the Dreamliner and A380 jets sapped cash.

"Clearly there is a vast amount of over-ordering," said Aengus Kelly, chief executive of AerCap Holdings NV, which owns 350 planes and is the number three global leasing company after the Gecas unit of General Electric Co. and ILFC, a unit of American International Group Inc. slated for an initial public offering.

Airbus and Boeing have over the past year built record order backlogs, selling hundreds of the revamped versions of their best-selling narrowbody planes, but Kelly cast doubt on whether some big deals such as involving Indonesia's Lion Air and Norwegian Air Shuttle AS would ever be realized in full.

"Is it realistic that a small airline in Indonesia is the largest customer of the world's largest exporter?" Kelly said of Boeing's 230-plane order from Lion Air, worth US$22.4 billion at list prices.

Boeing and Airbus have been sanguine about the production build-up, maintaining the demand is there as well as the funding.

"Airbus' production correlates precisely to real demand," said a spokeswoman.

A Boeing spokesman declined to comment directly on Kelly's remarks, but said "we feel our long-term market forecast, and our production-rate increases happening right now, are in line with true demand in the market."

The revamped A320 and 737 jets have secured hundreds of orders, often from still-small carriers such as Lion Air and Norwegian, which last month split a 222-plane deal between Airbus and Boeing.

Lion Air executives maintain orders that envisage as much as an eight-fold expansion of its fleet are justified by soaring domestic and regional demand. Their counterparts at Norwegian are similarly bullish, viewing opportunities in Europe's low-cost market to grow from a fleet that totaled 62 planes at the end of last year.

"I would be surprised if Ryanair and easyJet allowed a large competitor to emerge on their doorstep," Kelly said, referring to the region's two dominant discount operators.

Leasing companies have assumed an increasingly important voice in the airline industry as carriers opt to rent rather than buy, and account for over half of the global fleet of the newest and most in-demand planes such as the Boeing 737-800.

They have also been among the most pessimistic commentators about the ability of carriers to fund new purchases, and AerCap's Kelly admits its in their interest for plane makers to build as many as possible since it opens up more opportunities to snap up jets that airlines find tough to finance.

AerCap has taken an option to buy six Airbus A320neo jets ordered by an unidentified carrier that Kelly said "needed help," and he saw more opportunities from the yet-to-fly plane and its Boeing rival, the 737 Max.

Investor concern about aircraft demand has deepened in recent weeks as the combination of high fuel prices and tepid demand has claimed more than half-a-dozen airlines, including the collapse of large operators such as Spain's Spanair and Malev, the Hungarian flag carrier.

Kelly said distress levels in the industry still remained well below those seen in late 2008 and early 2009, tough it did step in and repossess two planes from India's struggling Kingfisher Airlines Ltd. and one leased to Global Aviation Holdings Inc., the U.S.-based charter specialist that filed for bankruptcy protection earlier this year.

He also said AerCap remains committed to a big leasing deal with AMR Corp., reached before the parent of American Airlines filed for bankruptcy protection.

AerCap last year agreed to buy up to 35 Boeing 737-800s ordered by AMR and has so far acquired six of them and leased them back to the airline, including two this month, with another nine due to follow this year.