Safety authorities are urging ATR pilots to be cautious over their airspeed during descent after highlighting a risk of severe propeller mechanism damage.
The advisory centres on sudden vibrations occurring during descent at speeds close to the maximum operating limit, with the power levers in the flight-idle position.
In a bulletin the European Aviation Safety Agency describes the phenomenon as an “airworthiness concern”, although it has not taken the step of producing a formal directive.
Onset of the vibrations has been linked to damage to the propeller pitch-change mechanism. EASA is aiming to improve pilot awareness of such events to prompt adoption of “conservative measures”.
The 30 January bulletin covers ATR 72-600s and ATR 42-500s fitted with Hamilton Sundstrand propellers.
EASA says pilots should follow closely the airframer’s recommendation for a standard descent speed at a maximum of 240kt.
If the speed approaches the maximum operating limit – known as Vmo – then any reduction of throttle to flight-idle should involve a “smooth and progressive” retardation of the power levers, it adds.
If the pilots should nevertheless encounter the vibration phenomenon during descent, they should try to identify, and shut down, the affected engine. The crew should avoid using ‘reverse’ mode on the engines if discrimination and shutdown proves difficult.
EASA says there is evidence that the mechanism damage was preceded by crews’ experiencing unusual vibrations when retarding throttles to flight-idle during high-speed descent, and that pilots should report such phenomena to their operator’s maintenance organisation.
Source: Cirium Dashboard
