GPS/RNAV Systems Flashcards
Give a BRIEF explanation about how the GPS system works generally (Segments, Basic function, RAIM/WAAS)
3 Segments:
Space - Satellites
Control - Ground Stations
User - GPS receivers
Satellites TRILATERATE your location using accurate ATOMIC CLOCKS to measure the time it takes for a signal to move between it and the receiver
RAIM - Monitors signal integrity
WAAS - eliminates any major ATOMIC CLOCK ERROR via ground stations
If your GPS is only RAIM capable, what considerations need to be taken concerning the choice of alternate airport filed?
Either your Destination or your Alternate must have a ground based approach available
What does having a WAAS capable GPS enable us to do concerning the choice of alternate airport filed?
Having a WAAS capable GPS enables us to choose an Alternate Airport that ONLY has an RNAV IAP available.
*This is because WAAS enables us to use GPS as our primary means of navigation.
Explain the WAAS system and how it functions.
38 Ground Reference Stations
3 Master stations - Correct for atomic clock error
6 Uplink stations
3 Geostationary Sats
How many Satellites are needed for RAIM to function properly?
- 5 Sats
- 4 Sats, if you have Barometric Aiding
How many Satellites are needed for RAIM to be able to isolate a corrupted signal?
6 Sats
- 5 Sats, If you have Barometric Aiding
*This is the Exclusion element in ‘Fault detection and exlusion’
Does our aircraft have DME?
No, we have GPS in lieu of DME
On a GPS approach, what are the following CDI sensitivity changes:
- Enroute
- Terminal
- Approach
Enroute
+- 2 NM (with RAIM, 5nm without)
Terminal
+- 1 NM, within 30 NM of the airport
Approach
+- 0.3 NM, when within 2 NM of the FAF
What happens when Approach Mode is NOT armed prior to at least 2 NM from the FAF? (3 things)
- Approach Mode will not automatically activate
- Sensitivity will not drop to Terminal levels of +- 0.3 NM
How many Satellites are required for the following GPS dimensions:
- 2D location
- 3D location
- RAIM
- RAIM + Exclusion
2D = 3
3D = 4
RAIM = 5 + Baro-Aiding (6 without BA), 6 Sats for Exclusion
Which is WAAS and which is RAIM only?
TSO 129/196
TSO 145/146
TSO 129/196 = Non-WAAS (RAIM only)
TSO 145/146 = WAAS equipped GPS
Explain how RNAV CDI sensitivity changes as we leave the Enroute environment
Enroute (ENR) = +- 2NM with WAAS (RAIM = 5NM)
Terminal (TRM) = +- 1NM when within 30NM from the airport
Approach (APP) = +- 0.3 NM within 2NM of the FAF with RAIM only, WAAS will continue scaling down starting AT the FAF to +- 700ft for LPV approaches
Missed Approach = +- 1NM once you pass the MAP and activate the missed
What is required to fly an LPV approach?
You MUST be WAAS equipped
- Baro-Aiding or RAIM are not enough to fly LPV
What is required to fly an LNAV/VNAV approach?
WAAS or a Baro-Aided GPS
- RAIM only is not enough to fly LNAV/VNAV
What enables the GPS to go down to the 350ft (700ft total width) full deflection accuracy in the approach environment?
WAAS.
- This enables us to perform ILS ‘like’ LPV approaches
- Without WAAS, the accuracy will not step down, and we cannot fly down to LPV mins.