GPS primary A320

[Speedwinner]

Hi folks,

Many pilots always check the gps primary feature before approach. I remember that the gps will announce a failure when accuracy is low and when we fly gps approaches we always have the page with the accuracy open. So anyway: can I rely on the fmgc or will there be situations, realistic ones, when the aircraft doesn't warn me?

Thanks!

[Skornogr4phy]

If the approach requires GPS then GPS must be primary. If it is just an RNAV approach/arrival that uses conventional navaids (DME/DME etc) then there is no requirement for it to be primary provided the NAV accuracy is above the required level.


Correct me if I'm wrong.

[Rocket3837]

Some operators require the GPS for any rnav star and appr regardless of the requirements on the chart.
Check yr airline policy
Thanks

[Speedwinner]

Thanks for the answers. Despite for what we need the gps my question was: if accuracy low is detected do we get a warning? Is it necessary to monitor the gps primary feature?

[CaptainMongo]

Hello, below are two excerpts from the "Thales New FM Pilot's Guide, Release 1A - Airbus 318/319/320/321". This is dependent on what OPC your company installed, but I would bet this is a pretty standard install world wide. The system self evaluates continuously, if the accuracy downgrades you will get a status message which is not clearable, therefore I would say no, you do not need to monitor the GPS primary feature.

Regards,




Nav Accuracy check

Refer to Operator's SOPs. Following procedures recommended, depending on availability of GPS:

l If GPS available: On PROG page,

GPS PRIMARY................. Check When GPS PRIMARY is shown (green), the Accuracy is invariably HIGH.

If "GPS PRIMARY LOST" (amber) appears in scratchpad and on ND, proceed as for GPS not available. ND message is not clearable.
POSITION ACCURACY

The following data related to Position Accuracy are displayed on the PROG page:

￿￿ GPS Status [5R]

GPSOPT [OPC] [A/C CONF]

OPC: GPS Option activated

For non GPS A/C this field is blank.

When both GPS accuracy and integrity requirements are met, the Confidence Status on GPS (autonomous system) or GPIRS (hybrid system) position is designated as GPS PRIMARY, displayed on PROG page [5R].

III_083_011_SA_00

If these requirements are not met, field [5R] is blank and GPS/IRS mode is lost; "GPS PRIMARY LOST" message (amber) is triggered on MCDU and ND of the affected side. It cannot be cleared from ND. When GPS/IRS mode is restored "GPS PRIMARY" message (white) is triggered on MCDU and on ND; GPS PRIMARY is again displayed in [5R].

[yusif831]

Even if GPS PRIMARY is lost you may still have accuracy HIGH. And yes aircraft will worn you if losse GPS.