A320 'GPS PRIMARY LOST'

[IFLY_INDIGO]

Does 'GPS PRIMARY LOST' message means that RAIM check is failed?

thanks in advance

[junebug172]

GPS PRIMARY is lost. This message is generated when:

- GPS/INERTIAL mode is lost, or
- Accuracy is downgraded from HIGH to LOW
while GPS confidence level was GPS
PRIMARY, or
- Accuracy is high and NAV mode is not
GPS/INERTIAL with GPS option active at
transition to Approach flight area.
This message is only displayed when GPS option is active. It is deleted if GPS PRIMARY is triggered.

[PappyJ]

No, RAIM is a different kettle of water.

A 'GPS PRIMARY LOST' message simply indicates that the GPS signal from one or both MMR(s) has been lost. You could get this through something as simple as placing a small sheet of steel over the antenna, having a wire come loose, or anything else that restricts the signal from reaching the receiver.

RAIM detects faults with redundant GPS pseudorange measurements. That is, when more satellites are available than needed to produce a position fix, the extra pseudoranges should all be consistent with the computed position.

This is obviously the short story. If you need more details, let me know.

[FlightPathOBN]

When you say RAIM check, that is an internal function of the system. For the system to determine horizontal and vertical position, at least 4 sats are needed.
To provide error detection in those measurements, at least 5 are needed.
To be able to detect, error detect, and isolate an error, at least 6 are needed.

The RAIM system will look at all of the avail data, and compare the required level of accuracy (ex 0.15 RNP) with the actual accuracy level of the system.

For GPS PRIMARY...

ESTIMATED is the measure of position accuracy.
If ESTIMATED value exceeds the REQUIRED value, NAV ACCUR DOWNGRAD is displayed.
FM position is reliable but not sufficient to continue.

GPS PRIMARY and HIGH accuracy must be present on BOTH MCDU PROG pages.
If GPS PRIMARY is lost, ESTIMATED position will increase with time.
FM position is reliable but not sufficient to continue.

[IFLY_INDIGO]

answer found in FCOM:

for GPS PRIMARY status two criterion should be met together :
1. ACCURACY should be HIGH
2. GPS integrity check should not fail (I guess, that is the RAIM)

anytime, one or both of these conditions not met, GPS PRIMARY status is lost and GPS PRIMARY LOST messages sticks to the ND.

[MD83FO]

Since the GPS subjet is open.. Can i fly an RNAV GNSS on a single GPS receiver?
Is there a reference outside of my MEL and Autoflight limitations?
Been searching PBN docs but o help.
Thanks.

[McMax]

Check your FCOM...

FCOM, Procedures, Normal Procedures, company Standard Operating Procedures, RVAV/RMP Approach

At least in our FCOM there is a table what's required and when it's a no go/go around...

[IFLY_INDIGO]

RNAV GNSS approach is a non precision approach. It should be permitted with one GPS receiver.

[Nightstop]

We require 2 GPS sensors & 2 FMGS in our company to fly a RNAV (GNSS) approach.

[vilas]

MD83FO
What Night stop has stated is correct. For RNAV GPS approach two navigation systems must be operative i.e. two FMGS and two GPS sensors. VOR DME managed approach only requires GPS primary or NAV ACC high and the conventional radio NAV aid must be available and monitored during approach and must be considered with altitude as the primary means of navigation. In other words for managed VORDME there is no mandatory requirement of GPS.