Lockheed Martin owes the US government at least $265 million after company employees discovered a five-year-old charging error on the F-35 Joint Strike Fighter programme.

Lockheed says it has inadvertently billed the government twice for award fee invoices paid since 2002 to its two major subcontractors - Northrop Grumman and BAE Systems. After the subcontractors were paid the first time, a coding error in Lockheed's billing system sent a second invoice for the same bill, which the government paid without question.

"We are working with our customer to ensure that enhanced controls will be put in place to prevent this from occurring in the future and will meet with their satisfaction," Lockheed says.

The company will reimburse the government by reducing future billings from this week. "We are working with the government to determine the appropriate amount of interest" owed, according to a released company dossier.

The government's joint programme office was unavailable to comment.

The overbilling issue was discovered during a "routine internal audit" by the company, Lockheed says.

The internal audit found that the overcharging issue dates back to the initial contract award period in 2002.

Lockheed says the discovery will have no impact on the company's previous financial reports and is not expected to have a "material effect" on the company's finances and operating results.

"We have initiated a thorough review to determine why the error was not detected sooner," Lockheed says, and "to prevent any recurrence of this type of billing error".

Source: Flight International