Sweden asks for flight limits for ATR72s

A number of incidents involve severe vibrations
The Swedish Accident Investigation Authority (SHK) has asked European regulators to set limits on how the ATR72 aircraft can safely fly, until the cause of seven separate severe vibration incidents over seven years can be determined.
It wants ATR and Hamilton Sundstrand, the maker of the aircraft’s six-bladed propellers, to find the reason behind the incidents, which took place between 2007 and 2014.
All of the reported vibration incidents have three elements in common – they all happened in the right engine, they occurred during descent at a speed close to 250 knots (287 mph), and when the power levers were reduced to flight idle.
“[Our] assessment is that additional extensive engineering initiatives are necessary in order to find the cause of the incident,” the SHK noted in its final report on a November 2014 case when a Braathens Regional ATR 72-200 experienced severe vibrations on approach to Visby Airport.
In that case, the vibrations became “so severe” that the cabin crew had “difficulty moving” and the pilots could barely read their instruments. The vibrations stopped when the right engine was shut down. No one on board was injured during that incident.
Aviation Week