If the spindle motor does overcome the excessive stiction, the head may go through some unpredictable motions when it breaks away creating the potential of media surface damage. The surfaces of the head and media are carefully optimized to reduce the dangerous effects of excessive stiction including the use of special lubricants on the media surface. Humidity and condensation have proven to be a significant cause of failure of commercial disk drives used in an airborne environment. Numerous failed disk drives have been carefully disassembled in a clean room environment, and analyses of the head and media components have confirmed the causes of the failures. Aircraft are frequently parked for extended periods of time with environmental control systems turned off, allowing equipment to experience the local external climate.
Condensation is prone to occur when environmental control systems are initially activated.
The magnetic parameters of both the head and media are sensitive to thermal effects. While the consequences of thermal extremes are not usually as catastrophic as humidity, reliable operation of the disk drive may be affected. This typically first manifests itself in high data error rates. Although the mass of the flying head continues to be reduced and the durability of the media surface continues to be improved, head slap caused by excessive shock can still damage the head and media surfaces leading to head crashes and catastrophic failures. The task of the servo positioning system is to provide a means for the recording heads to be accurately positioned over any track on a disk platter so that data may be recorded or retrieved.