Mr Sears was seen as a potential Boeing boss

Mike Sears helped hire Darleen Druyun, a US Air Force official, before she had officially disqualified herself from government service.

And the pair attempted to conceal their misconduct, an internal review found.

Boeing is attempting to carve out a reputation for impeccable ethics, after suffering a string of scandals in recent years.

In July, the firm was frozen out of some Air Force tenders after admitting spying on rival defence contractor Lockheed Martin.

"The Government stripped more than $1bn worth of satellite launch work from Boeing for having in their possession thousands of pages of documents in their possession belonging to Lockheed Martin who was a competitor in that business," Seattle Post Intelligence's Bill Virgin told BBC World Business Report.

"Boeing made a big show at that time of taking out big newspaper ads, of hiring a former US Senator to conduct an outside investigation of its ethical practices, of hauling employees around the country into various seminars on ethics.

"But then when you have this coming right on top of it, they may not [win over] prosecutors, investigators or critics by throwing an executive or two overboard," Mr Virgin said.

Illicit communication

Mr Sears, widely seen as favourite to succeed chief executive and chairman Phil Condit, joined Boeing in 1997.

Ms Druyun had inside information on Air Force procurement

He was president of the aerospace business at McDonnell Douglas, which was taken over by Boeing.

His misconduct arises from indirect communication with Ms Druyun over negotiations for a massive contract to convert 767 jets to military refuelling tankers.

According to Boeing's internal investigation, Ms Druyun - previously a top procurement official in the Air Force - passed on pricing data from Airbus, Boeing's closest rival in the international aviation market.

In return, the complaint implies, she was offered employment at Boeing.