One gps Failure
If there is one GPS failure, there is no annunciation until you push the system status annunciator panel assembly (recall). When you push the annunciator panel, these annunciations show:
GPS light on the IRS mode select unit
IRS light on the system status annunciator
Left and right master caution lights.
When you release the annunciator panel assembly, all the annunciations stay on until you reset by a push of either the left or right master caution light (reset).
Two gps Failures
If both GPS systems have a failure, these annunciations show:
GPS light on the IRS mode select unit
IRS light on the system status annunciator
Left and right master caution lights.
When you push and release either the left or right master caution light, the IRS light and master caution lights go out but the GPS light stays on.
GPS - CDU DISPLAYS
General
GPS data shows on the control display unit (CDU). The position pages show this data. These are the three position pages:
Position initialization (1/3)
Position reference (2/3)
Position shift (3/3).
You use the next and previous key to see all three position pages. These are the pages that show GPS data:
Position reference (POS REF)
Position shift (POS SHIFT).
POS REF Page
The POS REF page shows GPS L (1) and R (2) positions.
POS SHIFT Page
The POS SHIFT page shows the GPS position from the flight management computer (FMC) position. The GPS position shows in these two parts divided by a slash (/):
Bearing of the GPS position from the FMC position
Distance of the GPS position from the FMC position in nautical miles (NM).
Training Information Point
For all CDU displays that show GPS data, the displays refer to GPS 1 as GPS L and GPS 2 as GPS R.
The POS SHIFT page does not show information in the data fields when the airplane is on the ground.
GPS - TRAINING INFORMATION POINT – 1
General
The GPS has continuous monitor BITE. These are the three ways to detect GPS failures:
When both GPS system 1 and GPS system 2 have failures, the GPS fail light comes on.
When you push a master caution annunciator and a GPS system has a failure, the GPS fail light comes on.
The FMC SENSOR STATUS page shows MMR failures. The FMC SENSOR DATA page shows the internal failure in the MMR.
GPS - TRAINING INFORMATION POINT – 2
General
These are the two pages that show GPS maintenance data:
FMCS SENSOR STATUS page
FMCS SENSOR DATA page.
FMCS SENSOR STATUS Page
The FMCS SENSOR STATUS page shows the status of the GPS systems. It shows OK for systems that are valid and FAIL for a GPS system that has failed.
To get access to the engineering data for the failures, type 100 in to the scratch pad and select line select key 6 right (LSK 6R).
FMCS SENSOR DATA Page
When GPS L (1) or GPS R (2) has a failure, the engineering data will show. If both GPS systems are valid, no engineering data for the GPS systems will show on this page.
This is the data that will show:
System code
Label code
Fault state
Failure time
Monitor code.
GPS - MMR BITE
Front Panel Self-Test
When you push the test switch, the MMR does a check of the internal operation and its interface with the GPS antenna. The test takes approximately 36 seconds. This is the test sequence that shows on the status LEDs during the test:
0 to 2 seconds, the LRU STATUS and the CONTROL FAIL
LEDs are red
2 to 4 seconds, the LRU STATUS LED is green and the
CONTROL FAIL LED is red
4 to 6 seconds, all LEDs go off
6 to 36 seconds, test status shows.
NOTE: The ANT FAIL LED is not used at this time.
The LRU STATUS LED shows red when there is an internal failure in the MMR. A green LED shows that the MMR is normal. The CONTROL FAIL LED shows red when an interface to the MMR has a failure.
