How is the drift corrected in INS-driven attitude/heading indicators?
Inertial navigation systems do not need to correct for drift.

Modern optical gyroscopes drift about 0.001°/h and even the mechanical ones used aboard the apollo spacecraft back in 1969 achieved 0.03°/h (see Apollo 8 Mission Report, page 119). After a 20h-flight with those mechanical gyros, accumulated drift would be 0.6° and therefore less than the error of a self-erecting, ordinary attitude indicator during a turn.

The reason ordinary attitude indicators need an erection mechanism is not that they are imprecise, it is because earth turns and the aircraft moves.


Earth turns at a rate of 15°/h at the equator and 0°/h at the poles. The attitude indicator must adapt to the unknown drift unless it knows its latitude, in which case the drift is also known.
Aircraft travel considerable distances. The local horizon in Cape Town (34°S) differs from the local horizon in Berlin (52°N) by 86°. An attitude indicator must correct for these changes as well, unless it knows it just travelled from Cape Town to Berlin.


Inertial navigation systems do not suffer from these issues. They know their position, the route they travelled and how long they've been flying. They just leave the gyroscopes as is and apply corrections to the display only.