Aircrew members must use their knowledge and training to protect themselves and to prevent injuries caused by noise and vibration. Noise is sound that is loud, unpleasant, or unwanted. Vibration is the motion of objects relative to a reference position, which is usually the object at rest. In aviation, both may cause annoyance, speech interference, fatigue, and hearing loss. Noise energy is undesirable when attention is called to it unnecessarily or when it interferes with routine activities in the home or while flying an aircraft.
Individuals become annoyed when the amount of interference becomes significant.
High-frequency noises and vibration are especially irritating and can cause a subjective sense of fatigue. When noise and vibrations reach a certain loudness or amplitude, they mask normal speech communication. Thus, words become difficult to understand. The most important and common undesirable effect of noise is permanent hearing damage. Excessive vibrations can manifest themselves in terms of internal organ malfunctions and skeletal disabilities.