The regulator is imposing a new 'flight directive' on Dreamliners, meaning planes could be grounded if they don't undergo additional rounds of inspections and records checks to make sure parts including the aileron and elevator power control units are still working properly.

Shares dumped as this news added to anxieties about a weekend report about Boeing's failure to alert the FAA and Southwest, its biggest customer, that it had disabled an important safety feature on the 737 MAX 8.

Still, Boeing shares are - incredibly - still up 17% on the year.