They call them the boneyards, the places where elderly aircraft go to die, but in the normally silent desert cemeteries for the old and the unwanted the sound of alarm bells is being heard by the multibillion-dollar aircraft-leasing industry.

The boneyards, which had been emptying steadily since the airline industry suffered the catastrophic blow of the 9/11 attacks, are beginning to fill again — and that is bad news for the leasing companies that are beginning to suffer sharp falls in the value of older planes.

As banks and oil company creditors pull the plug on struggling airlines, the blow will rebound on investors in aircraft leases. Fitch, the ratings agency, issued warnings in July that record jet fuel prices and waning demand for air travel were raising the risk of default on aircraft leases. Fitch has switched its rating outlook to “negative” for the entire aircraft securitisation industry and last week said that the outlook remained poor despite the recent fall in crude prices.

Aircraft values are beginning to tumble again after recovering post-9/11. Values for older, less fuel-efficient aircraft are crumbling.

Paul Leighton, managing director of Aircraft Value Analysis Company, said that the price of older planes, such as the Boeing 737-300 series, had fallen by a fifth this year and the slide would continue in 2009. “Generally,” he said, “the market for older aircraft will be a problem and for newer aircraft it will be more difficult. Lessors will start to struggle. It may take four, five or even six months to find customers.”

The demise of XL, the charter airline, and the desperate, eleventh-hour efforts to pay Alitalia's daily fuel bill highlight the problems that may begin to affect aircraft-leasing companies. These include GECAS, the leasing vehicle owned by GE Capital, International Lease Finance Corporation (ILFC) and CIT Leasing Corporation.

Most airlines do not own aircraft but rent them from leasing companies. These often will package the income from a portfolio of leases and sell them to investors, such as banks and other financial institutions, to raise cash to buy aircraft. These securitised loans, not unlike the mortgage-backed securities that are causing problems for the banking sector, may now rebound on investors as airlines default on the rents and the value of aircraft dwindles.

XL had 20 aircraft leased from institutions, including GECAS and ILFC, but these were mainly newer planes that should find new homes. Alitalia is different. Its fleet of more than 180 aircraft is elderly, including many MD-82s and old Airbuses, which are costly to run and, therefore, unattractive. A failure of Alitalia would dump these aircraft on to a market that is about to become saturated with old planes.

Fitch says that the recent cuts in capacity by big carriers, including American Airlines and Ryanair, as well as bankruptcies and fleet liquidations, will mean more grounded aircraft just as Boeing and Airbus are increasing production of new models. “These grounded aircraft, coupled with the record number of deliveries scheduled for the next several years, could create a considerable shift in the supply and demand balance for commercial aircraft.”

Mr Leighton agrees. “We have a long backlog of orders [for new planes] equal to four years' production and we have high oil prices,” he said.

According to Mr Leighton, the price of a 737-300 could fall to only $5 million (£2.79 million) next year, half its value in 2006. Even more efficient aircraft, such as the 737-800, are suffering 10 per cent drops in value. The oldest aircraft, such as early 737s built in the 1970s, can be bought for just $200,000, but the cost of fuelling and servicing them is almost prohibitive.

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