What cause INS to stop at at 6.9?

1- Engines should be OFF

2- Parking brake ON
3- APU/Exterior power ON
4-Don'T move the Aircraft
5-???

Thanks
Sanal

Hmmm a very tricky question...It may be a default setting, or sometimes electrical signals, like ground power and APU coming from the same places, could cause the same reading contantly while shut off. These sytems, like APU aren't meant to be running while INS and other instrument things are running. As long as the Inertial Navigation System functions fully and accurately all the time, its no issue.