GPS/RNAV Systems

Question 1

Give a BRIEF explanation about how the GPS system works generally (Segments, Basic function, RAIM/WAAS)

Answer 1

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

Question 2

If your GPS is only RAIM capable, what considerations need to be taken concerning the choice of alternate airport filed?

Answer 2

Either your Destination or your Alternate must have a ground based approach available

Question 3

What does having a WAAS capable GPS enable us to do concerning the choice of alternate airport filed?

Answer 3

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.

Question 4

Explain the WAAS system and how it functions.

Answer 4

38 Ground Reference Stations

3 Master stations - Correct for atomic clock error

6 Uplink stations

3 Geostationary Sats

Question 5

How many Satellites are needed for RAIM to function properly?

Answer 5

• 5 Sats
• 4 Sats, if you have Barometric Aiding

Question 6

How many Satellites are needed for RAIM to be able to isolate a corrupted signal?

Answer 6

6 Sats

• 5 Sats, If you have Barometric Aiding

*This is the Exclusion element in ‘Fault detection and exlusion’

Question 7

Does our aircraft have DME?

Answer 7

No, we have GPS in lieu of DME

Question 8

On a GPS approach, what are the following CDI sensitivity changes:
- Enroute
- Terminal
- Approach

Answer 8

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

Question 9

What happens when Approach Mode is NOT armed prior to at least 2 NM from the FAF? (3 things)

Answer 9

1. Approach Mode will not automatically activate
2. Sensitivity will not drop to Terminal levels of +- 0.3 NM

Question 10

How many Satellites are required for the following GPS dimensions:
- 2D location
- 3D location
- RAIM
- RAIM + Exclusion

Answer 10

2D = 3
3D = 4
RAIM = 5 + Baro-Aiding (6 without BA), 6 Sats for Exclusion

Question 11

Which is WAAS and which is RAIM only?

TSO 129/196
TSO 145/146

Answer 11

TSO 129/196 = Non-WAAS (RAIM only)

TSO 145/146 = WAAS equipped GPS

Question 12

Explain how RNAV CDI sensitivity changes as we leave the Enroute environment

Answer 12

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

Question 13

What is required to fly an LPV approach?

Answer 13

You MUST be WAAS equipped
- Baro-Aiding or RAIM are not enough to fly LPV

Question 14

What is required to fly an LNAV/VNAV approach?

Answer 14

WAAS or a Baro-Aided GPS
- RAIM only is not enough to fly LNAV/VNAV

Question 15

What enables the GPS to go down to the 350ft (700ft total width) full deflection accuracy in the approach environment?

Answer 15

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.

Question 16

What is required to fly an LP approach?

Answer 16

You MUST have WAAS in order to fly an LPV approach
- RAIM (basic IFR GPS) or Baro-Aiding is not enough to fly an LP approach.

Question 17

Are we able to fly approaches with ‘(RNP)’ in the title?

Answer 17

No,
- Requires a letter of authorization from the FAA and special equipment/training to fly.
- They are similar to CAT II & III ILS approaches

Question 18

What should you do if you encounter a RAIM failure while on an RNAV approach?

Answer 18

1. Go missed
2. Report to failure to ATC (required)
3. Switch to Ground based navaids

Question 19

How will you know if your WAAS or RAIM issues a failure?

Answer 19

You will see a yellow ‘LOI’ (Loss of Integrity) annunciation appear on the HSI.

Question 20

What happens at 2 NM from the FAF in regards to GPS integrity?

Answer 20

The GPS will perform a RAIM prediction and notify you with ‘LOI’ if there are any issues with the GPS

Question 21

How do you know your aircraft is IFR certified to perform LPV approaches?

Answer 21

The G1000 Supplement to the AFM states that our aircraft is TSO-146 and approved for GPS approaches

Question 22

How does ADS-B work?

Answer 22

1. Satellites communicate with the aircraft to determine position
2. ADS-B OUT sends that GPS derived information to ground stations
3. Ground stations send the location information to ATC and aircraft with ADS-B IN

Question 23

How often does ADS-B GPS information update a location position?

Answer 23

About once per second

Question 24

What does TIS-B add to ADS-B?

Answer 24

Traffic Information Service Broadcast (TIS-B) completes the ADS-B IN traffic display picture by adding aircraft equipped with a Transponder only, and not ADS-B OUT.