Magnetic disk apparatus and off-tracking detection method

A method of controlling a positioning of a first head on a first disk surface in a disk apparatus comprising

• a first medium having the first disk surface on which first servo patterns are recorded, wherein the first servo patterns are to be read at a first timing and data is to be wrote on the first disk surface by using the first head, and
• a second medium having a second disk surface on which second servo patterns are recorded, wherein the second servo patterns are to be read at a second timing different from the first timing by using a second head, the method comprising:
• controlling the first head based on a first demodulated position and a control target position, the first demodulated position being obtained by demodulating the first servo pattern
• calculating a first estimated demodulated position from the first demodulated position and a first demodulated velocity based on the first servo patterns,
• calculating a second estimated demodulated position from the first demodulated position and a second demodulated velocity based on the second servo patterns, each of the second servo patterns being read after reading each of the first servo pattern, and
• stopping data writing operation of the first head in accordance with one of the first and second estimated demodulated positions exceeding a particular threshold.