It is likely to define the rules of the civil aviation market for years to come.
The World Trade Organisation is expected to confirm criticism of European aid for Airbus when it issues a final ruling on subsidies.
This is by far the biggest international trade dispute the WTO has handled.
The US argues that Airbus got a total of 151 billion euros in unfairly priced loans and other benefits from France, Germany, Spain and Britain over two decades.
But the EU is likely to argue that the full picture will only emerge when the WTO rules in turn on a countersuit brought by Brussels.
The decision, although final, is confidential and the result is not expected to be known straight away.
In theory, a WTO ruling could require the EU to end further aid within weeks. In practice, both sides are likely to appeal both cases, stringing litigation out for years.