We recently worked on a VG206D vertical gyro that required a complete overhaul. After landing and powering down the avionics, the aircraft was moved by a tug, which turned hard left to get off the ramp.
It takes 20 minutes for the gyro’s spin motor to completely spool down. In this case, the aircraft was moved (without reapplying power) after roughly eight minutes, and the gimbal slammed into the stops, which damaged the gimbal and rotor bearings.
As a result, we saw precession errors and failures to erect on this gyro. Overhauling the gyro cost several thousand dollars and took nearly 35 hours.
Preventing these problems is fairly easy: Once you arrive at your destination and power down the avionics, give the gyros at least 20 minutes to spool down before moving the aircraft without power.
Failure to allow your gyros to fully spool down before moving the aircraft can cause severe damage. This video narrated by Randall Bauer, Duncan Aviation Gyro Master Tech, demonstrates what happens to a gyro when it is moved too soon.
Collins Aerospace TDR-94D Transponders
Performance Based Navigation