The FAA has always been very pro-active about grounding planes that are unsafe. The airlines operating these aircraft do not benefit by continuing to fly them if they are un-safe. Between the cost of the loss, public image etc. it would not make economic sense.

Given the trade tensions the US has with both China and the EU and the fact that both are offering competing products (Airbus more so), this sounds like more of a political move. In the case of the EU, the WTO ruled that Airbus was illegally subsidized by the government that has now banned a Boeing aircraft while it has the green light to fly in the US.

As swampy as the US government is, the EU has it's fair share of payoffs etc.. I expect this to further heat up the trade war.