The US National Transportation Safety Board says flight control design issues with the Zenair Zodiac CH 601 XL special light sport aircraft (S-LSA) make it susceptible to flutter and that the FAA should ground the aircraft until the problem is fixed.
Aerodynamic flutter, described by the NTSB as a "phenomena where the control surfaces of the airplane can suddenly vibrate, and if unmitigated, can lead to catastrophic structural failure", is suspected in six fatal accidents of the type, four in the US and two in Europe since 2006. In all cases the two-seat aircraft broke up in flight, killing a total of 10 people.
The Netherlands in October 2008 grounded Dutch registered XLs over similar issues after a fatal accident there.
The video below shows the basic attributes of the aircraft.