This past April, the NTSB called upon the FAA to ground the entire fleet of Zodiac aircraft because their wings tend to fall off in mid-flight.  As it turns out, a defect in the Zodiac’s design induces an aerodynamic phenomenon known as flutter.  Flutter can destroy a wing or other control surface in a matter of seconds.  This well-known, dangerous, but rare condition is shown occurring in the tail surfaces of other aircraft types here and here. 

When the NTSB’s issued its "urgent recommendation," a total of ten people had already been killed in Zodiacs due to flutter-induced failures.  Back then, the NTSB was under heavy fire for sitting on a long list of NTSB recommendations pertaining to a number of different aviation industry sectors while lives were being lost. Because of that, I figured that this was one recommendation the FAA would act on, and fast.

The FAA will see Zodiac’s manufacturer as an easy target and move against it — if for no other reason than to quiet its critics.

I was wrong.  The FAA refused to ground the aircraft.  Even I was surprised.

Of course, it was just a matter of time.  On November 6, another Zodiac crashed in Arkansas.   It looks like another flutter-induced failure.  That brings the death toll to 11.  On November 13, the NTSB issued an official "I told you so."

The Safety Board’s urgent recommendation to the FAA was to "prohibit further flight of the Zodiac CH-601XL, both special light sport aircraft and experimental, until such time that the FAA determines that the CH-601XL has adequate protection from flutter." The FAA replied in July that they lacked "adequate justification to take immediate certificate action to ground the entire fleet." 

The NTSB’s unstated question:  Just how many deaths are required before the FAA finds "adequate justification" to act?