▩A320▩predictive Gps

[A340SR]

Dear A320 drivers....
Thank you all in advance....

Everytime I see this "PREDICTIVE GPS" on 3L of PROG page,
I get really curious why, and when ... should I use this.....

FCOM only shows how it works, not about the REASON for this
function...

[smashin']

its a feature which is not really required at the moment, but in the future when we are all flying GPS approaches the predicitive GPS function looks at your ETA at arrival (or at a given waypoint) and calculates if you will have sufficient GPS coverage. It shows this either as a Y or an N for yes or no for various times before and after your ETA. It will prob all be Y's when you look at it but just play about with it and deselect some GPS's (this wont actually deselect GPS's but just carries out the predicitve GPS function as if that particular GPS satelite signal had failed). I think you enter the number of the satelite (1-24???) to deselect and you will start to see some N's appearing. ie. you wouldnt have sufficient GPS coverage to fly a GPS approach at that time if those satelites failed.

Good luck.

[Down Three Greens]

In the absence of any other check it could allow you to dispatch on RNAV(GPS) minima prior to depature. Only available on Honeywell ADIRU's not on the Litton version.

The deselected satelite number is the PRN (Psuedo Random Noise) Number of the particular satelite that's u/s.

[guiones]

From Honeywell FMS Pilot Guide:

The Predictive GPS page displays information about GPS integrity and availablility at the ETA(and for intervals before and after) for the destination and an entered waypoint.

Y (yes) or N (no) is displayed below the ETA and + or - time intervals in line 2 to indicate whether GPS is predicted to be available as primary means of navigation at the destination.

The pilot can enter a waypoint in 3L for the system to run predictions at that waypoint. After a waypoint is entered in 3L, boxes are displayed in 3R to enter the ETA for that waypoint.


Hope it helps!

G

[steven938]

On other systems this facility is known as RAIM - Receiver Autonomous Integrity Monitoring and reprts different levels of accuracy and whether the system is only suitable for en-route use up to let down & approach.

Hope this helps.

[LLLK]

Receiver Autonomous Integrity Monitoring (RAIM) is the ability of the GPS receiver/nav system to confirm that the satellites that is using to calculate its position are serviceable (healthy). RAIM needs 5 satellites in view to make the calculation (Fault Detection) and 6 if the faulty satellite is to be identified as well (Fault Detection and Exclusion) There are 3 protection levels - en-route (2NM), terminal (1NM) and final approach (0.3NM0

If you are planning to fly a GPS approach, or even to fly GPS-based RNAV routes in the US or Europe, you are required to perform a RAIM prediction before take-off. The RAIM prediction should determine how many satellites will be in view at any point along your planned route. The RAIM prediction algorithm in the airborne receiver uses information about the current status of the satellite constellation, received via the satellites themselves, however it has no knowledge of planned outages. RAIM prediction services such as those provided by Augur (http://augur.ecacnav.com), the FAA (http://www.raimprediction.net) and flight planning systems like Jeppesen take account of the planned outages as well.