I'm trying to better understand this concept and how it is used on later and updated Boeing aircraft.
Traditionally, when a particular autopilot is engaged, the ADC which supplies data to that autopilot is used as a reference and at least one of the pilots' altimeters should match the selected Mode Control Panel altitude.
However, along came "inertial altitude", and now pilots tell me that the autopilot can hold an altitude which agrees with none of the altimeters.
The question is... under what circumstances does this happen?
Is it a short term thing which happens during, say, turbulence?
Is inertial altitude only active in VNAV mode?
Does it only happen when an aircraft reaches a particular altitude and the autopilot locks in a barometric setting, thus allowing a pilot to change his/her baro setting without making the aircraft move up or down?
My engineering training notes are ambiguous at best
Thanks for any insight
Rgds.
NSEU