Well it's pretty confusing!
So here is what I have understood:
FMGS has got 3 different positions:
- GPIRS: calculated by the ADIRU. ADIRU get's GPS information with the MMR and 3 IRS/IRU/INS positions. ADIRU will then calculate a GPIRS hybrid position. It will basically make out one position.
It will then send the GPIRS position, the 3 different IRS/INS/IRU positions and the GPS position to the FMGC. (To the FG, I suppose)
We can see it here:
So, with this, the FMGS knows the GPS position and the GPIRS position. Now, the FMGS will calculate the MIX IRS position. But as IRS always drifts, it will use, if available:
a) GPS. GPS will correct IRS positions to calculate the IRS MIX POS. But If GPS fails, the plane will use:
b) Radios to correct IRS positions. So radios are basically navaids: VOR's (Airbus only autotunes VOR's as navaids).
But If the antenna's or the navaids fail, the plane will use:
c) BIAS to correct IRS position. BIAS is just a system which uses FMGS data to update/correct IRS MIX position.
The FG will send to the FM the GPIRS position (computed by the ADIRS).
If GPIRS fails, FG will send to FM the IRS MIX position.
If GPIRS and IRS MIX position fails, FM will use FM calculated position.
1) a) Do you agree with all this?
b) If IRS fails, will FG send to FM the GPS position or will it let FM calculate the FMGC position?
2) What does ADIRU use to correct IRS position to calculate GPIRS position? Only GPS? Or does it have BIAS too? Kalman filters? I don't think it get's radio update...
Now, I had found this post:
http://www.pprune.org/tech-log/40332...-position.html
So it says:
"Kalman filtering is a technique implemented in the FM, and applied
by the FM in order to compensate for IRS error.
As we know, IRS error grows with time.
It is interesting to note that as far as IRS versus GPS precision is
concerned, the IRS is less precise in long term but more precise in
short term.
The FM will compare the position obtained by the GPS (or computed
using Radio update), with the IRS raw position, the difference will be
translated into an error, and fed to the Kalman filter.
The Kalman filter will use the error and apply a correction based
either on the frequency or the statistical occurrence of that error."
3) Can we say that Kalman filtering is inside the
FM and BIAS are inside the
FG?
4) It also says:"On the Thales/Smith FMS position is a computed position, elaborated by the FMS, using Hybrid GPS/IRS position provided by the FG.
They use a Kalman filter, to cater for the drift and maintain a high accuracy."
So basically it uses the GPIRS position which it then corrects with the Kalman Filter??? But isn't it already corrected by the ADIRU while calculating GPIRS position? But he puts a "/" between GPS and IRS. Does he mean that the FM will make out another GPIRS hybrid position?