Aircraft noise and vibration in helicopter operations create a safety issue. From AIAA news

Rosekind Says Pilot Fatigue Remains Top Issue. Aviation International News (2/13, Mark) reports the NTSB’s Mark Rosekind told the Heli-Expo audience this weekend, “Fatigue in the aviation industry has been on the NTSB’s Top 10 Most-Wanted list for two decades. … It still makes up six of our top 10 fears today.” Rosekind “dove right into the fatigue issue at the lead-off educational session at Heli-Expo 2012 in Dallas.” He said “aircraft noise and vibration in helicopter operations create special fatigue issues, as does the predominance of single-pilot, on-demand operations, often conducted at night.