chapter  17
4 Alignment process
Pages 3

A fundamental requirement of inertial navigation

is the initial alignment process; this is required to

determine a local vertical and direction of true

north. Alignment must be carried out with the

aircraft on the ground and stationary. (Note that

in certain cases, e.g. on the flight deck of an

aircraft carrier, alignment has to be accomplished

whilst the aircraft is moving. In this case, an

external reference is required, e.g. the carrier’s

own inertial navigation system.) Systems using an

electromechanical gimballed platform need this

time for the gyros to level the platform with

respect to the local vertical and align the platform

in the direction of true north. For strap-down

systems, there is no platform as such; however,

the system still needs to establish a local attitude

reference and direction of true north for

navigation purposes.