Hello there,
I'm studying IRS at the moment and would like to submit a question regarding what exactly is drifting during their operation.
My understanding is that full alignment consists in "calculating" attitude based on gravity sensing, calculating latitude based on earth rate (which is compared to pilots "entered" latitude), finding true north by comparing A/C axis to the direction "vertical to earth rotation axis".
Now, after a flight, drift will have occurred and will be sort of "measured" in terms of residual GS and position discrepancy which both will have to be within "acceptable" margins.
1) May I then ask what would be the manufacturer margins for a 737 classic (no GPS)
2) In the situation where a quick align is decided for the following sector - which I understand consists in merely "zeroing" position and residual GS, what exactly in the IRU is "left" with a drift subsequent to the previous sector ? Are these both attitude and True North orientation ?
3) 737 classic (no GPS):
What exactly does the IRS transfer switch when switched to one side with regards to the opposite side connection with the FMC ?
Let's say transfer switch is selected to "both left", what is resulting of this sole action with regards to the R IRS connection with the FMC ?
Many thanks