14 CFR § 29.771

The compartment and its equipment must allow each pilot to perform his duties without unreasonable concentration or fatigue;

If there is provision for a second pilot, the rotorcraft must be controllable with equal safety from either pilot position. Flight and powerplant controls must be designed to prevent confusion or inadvertent operation when the rotorcraft is piloted from either position;

The vibration and noise characteristics of cockpit appurtenances may not interfere with safe operation;

Inflight leakage of rain or snow that could distract the crew or harm the structure must be prevented.