Further to the Shehbazis post...
Every aircraft in the world whether prop, jet , single engine, four engine, rotary, fixed wing, F-22 or P-51 Mustang or Airbus 380, there is one piece of equipment that has always been there and will always be i.e. Standby Heading Compass……
No matter how sophisticated the Navigation computer systems becomes , they will always remain a chance that these can fail due to their dependencies on aircrafts electric system or may be other external inputs etc..Whereas S’by compass is independent of any external input and can still operate if everything else fails.
However, one inherent problem of S’by compass is that it can give erroneous heading information due to various reasons as mentioned by Shehbazi. So there the need arises to keep this compass synchronised all the time, therefore a Compass Swing is carried out…
How compass swing is carried out is simple…You start your aircraft, taxi it to the designated compass swing area…A ground crew will assist you and ask you to turn the aircrafts on different headings, at each position on the ground, on a piece of paper you also note the difference between correspondent parked heading and the heading on the S’by compass……
After noting the difference on 6 or 7 different headings, you switch off the aircraft, hand the paper to Ground crew and he will first curse you for your bad hand writing, with a heavy heart he will tighten few nuts here and there on the compass , make an entry in the aircrafts form and ..Compass Swing is done…
I think this procedure may be difficult in areas close to the poles, esp North Pole, where the compass is not accurate. I think its here that the difference between True North and Magnetic North comes into play. I dont know if in our area, there is any difference between TRUE or MAGNETIC NORTH.
You are right…Close to Geographical North/South poles and Magnetic N/S poles, the S’by compass is useless…It gives huge errors in reading and one cannot rely on it. It also gives errors during acceleration/deceleration and during turning as well…S’by compass neither aligns itself with True nor Magnetic north, rather its orientation is with Compass North…