Exclusive - WTO judges fault Boeing subsidies -- sources

By Tim Hepher

PARIS (Reuters) -- The World Trade Organisation has broadly upheld a ruling that Boeing Co (BA.N: Quote, Profile, Research) took billions of dollars of unfair subsidies, breathing new life into an epic trade spat that has already faulted European aid to Airbus, people familiar with the matter said.

The world's largest trade dispute, involving mutual claims of aid to the dominant planemakers, reaches a crucial point on Monday when WTO appeal judges are expected to complete a pair of investigations by publishing their verdict on aid to Boeing.

At stake is whether the world's largest planemakers can continue to benefit from alleged public aid for heavy investment in new aircraft, but most analysts say it may be years longer before the complex legal processes are finally exhausted.

The two sides accuse the other of receiving billions of dollars in sham contracts or easy loans, while potential competitors in China, Canada, Russia and Japan are closely watching the case as they prepare to break open the duopoly.

A WTO panel ruled last year that Boeing had received at least $5.3 billion (3.3 billion pounds) in subsidies through research contracts mainly from space agency NASA as well as a series of tax breaks.

The findings followed a six-year probe into European Union claims that Boeing had received over four times that amount.

The EU filed the complaint as a counter-suit to U.S. claims that Airbus (EAD.PA: Quote, ProfileMens Nike Cortez