Originally Posted by
pineteam
Hello.
Very detailed summary, thank you!
Even tho I have been flying for a while on Airbus, I’m still unclear about the difference between these 2 —>
3IRS/GPS: Is it combined with both GPS? If not then what is the difference with FMGC1 or FMGC2 position as my understanding each FMGC uses a mix of 3 IRS + GPS1 for FMGC1 and GPS 2 for FMGC2.
GPRIS: “Current selected ADIRU GPRIS”? Don’t they always use all 3 IRS and one GPS to compute FMGC position?
Ok this is the way I understand it.
"Current selected ADIRU GPIRS" ===> Normally in this case it's the onside GPIRS (following the priority logic).
Normally MCDU 1 is connnected to FMGC 1 and MCDU 2 is connected to FMGC 2. Again in normal ops the FMGCs use their onside ADIRU GPIRS (remember the system selects ONE of the three available ADIRU supplied GPIRS)
MCDU 1 POSITION MONITOR page shows GPIRS of ADIRU 1 (if the ADIRU is operative)
MCDU 2 POSITION MONITOR page shows GPIRS of ADIRU 2 (if the ADIRU is operative)
Normally each ADIRU (1 and 2) selects one of the two GPS receivers to compute their GPIRS position, this selection is based on which GPS receiver is the most "accurate" considering their FOM or HIL.
3IRS/GPS ====>.
3IRS means that three ADIRUs are operative, 3 inertial positions are being used (MIX IRS), GPS I believe is the onside ADIRU GPIRS (again GPIRS 1 for FMGC 1 supplied by ADIRU 1 and GPIRS 2 supplied by ADIRU 2 for FMGC 2)
The FMGCs use a priority logic to select the GPIRS position for FM computation in GPS PRIMARY. Normally first priority is given to it's onside ADIRU in this case ADIRU 1 supplies it's GPIRS position to FMGC 1 and ADIRU 2 supplies it to FMGC 2. If the onside ADIRU fails then the FMGCs switch to GPIRS 3 supplied by ADIRU 3. Final priority is given to the offside GPIRS, FMGC 1 will use GPIRS 2 and vice versa.
Now ADIRU 1 may for example select GPS MMR1 (or GPSSU) for that ADIRU to compute it's GPIRS but the next flight it may select GPS MMR2! The ADIRUs are VERY picky and they always choose the most accurate of the two installed GPS receiver positions to compute their GPIRS.
Could be wrong so please correct if I'm mistaken.
The A320 is a nerd's aircraft, I love it! I hope I get to fly one here in the next 10 - 15 years.