GPS/RNAV

What is RNAV?

Allows navigation on a desired path without the need to overfly ground based facilities

What is GPS

GPS is a Global navigation satellite system that is operated by the United States

Around the world their are other kinds of GPS but they are all considered GNSS

What are the types of RNAV?

Global navigation satellite system (GPS)

VOR/DME RNAV
DME/DME RNAV

• Determing your point from a station by knowing distance/direction

Inertial reference system

What are the published RNAV routes?

Q routes - FL180 to FL450

T routes - 1200ft to 18,000ft

These routes are designated as RNAV 2 unless charted as RNAV 1

MRB - Magnetic reference bearing - The bearing between two waypoints on an RNAV route

What is the difference between RNAV 1 and RNAV 2

RNAV 1 - Aircraft must maintain a total system error of not more than 1NM 95% of the time

• RNAV 1 is found on SIDs and STARs

RNAV 2 - Aircraft must maintain a total system error of not more than 2NM 95% of the time

• RNAV 2 is found on T routes and Q routes

What is PBN

Performance based navigation

General basis for navigation equipment standards in terms of accuracy, integrity, availability that changes based on the phase of flight

A certain accuracy must be met to comply with PBN accuracy requirements at lest 95% of the flight time

What is RNP

RAIM but for RNAV it tells you the accuracy of the system and its how well it is performing

RNP is a specific statement of PBN for the flight segment and aircraft capability.
RNP is also defined as RNAV + navigation monitoring and alerting functionality

All RNAV approaches are RNP approaches

RNAV (GPS) - Title of most RNAV approaches in the US
RNAV (RNP) - Requires special FAA approval for the crew, aircraft, and operatoin

What are some examples of RNP?

Enroute - RNP 2.0 (2NM accuracy 95% of the flight time)

Terminal & Departure - RNP 1.0 (1NM accuracy 95% of the flight time)

Final approach - RNP 0.3 (0.3NM accuracy 95% of the flight time)

What are the different types of GPS approaches (DA)

LPV (DA) approaches increase in sensitivty after the FAF
Vertical guidance comes from a glidepath, use the lateral guidance from the GPS
WAAS

LNAV/VNAV (DA) approach has the same sensitivity after the FAF
Vertical guidance comes from something external to the GPS like altimeter, use the lateral guidance from the GPS
WAAS, GPS with baro VNAV

What are the types of GPS approaches (MDA)

LNAV (MDA) -
Fly the stepdown fixes and use the lateral guidance from GPS
WAAS, GPS with baro VNAV, Non-WAAS GPS

LP (MDA) - approach increases in sensitivity after FAF but doesnt have a glidepath
Fly the stepdown fixes and use the lateral guidance from the GPS
WAAS

LNAV+V (MDA) - NOT AN OFFICIAL TYPE OF GPS APPROACH
Vertical guidance comes from an glidepath for advisory purposes only
Many airport have GPS approaches that don’t have LPV mins, you are still flying an LNAV approach so use LNAV
WAAS

What is the satellite consillation?

The satellite constillation is 24 geosynchronous satellites

• 6 different orbital planes

• 4 satellites per plane with room for a spare

• 30 satellites max

• Orbits above the Earth at 10,900NM

At any point on the globle…

4 sats are always avaliable but typically 6-8

What does the term geosynchronous mean?

All move with the Earth’s rotation and the orbital period is half a day or 11 hours and 58 minutes

How are sats oriented?

They are oriented so solar panels face sun and anetnnas face Earth

What are the components of sats?

Solar panels

Antennas

Atomic clock

Radio transmitter

Pseudorange

Distance between sat/receiver including path delays

Calculated based on time it takes for signal to travel from sat to receiver

What are the components of the ground control network?

Master control station

Monitor station

Ground based antenna

Master control station

Makes commands that control the satellite constellation

Performs MX

Anomaly resolution by repositioning satellites

Monitor station

Collects data from satellites in constellation

Pseudorange measurements are made to each satellite in view and are used to update the MCS estimate of each sats position in orbit

Sends data to MCS, 16 around the globle

Ground based antenna

Sends commands and navigation data, uploads to the sats

11 around the globe

4 GPS antenna

User equitment

Processes L band signals from sats for computation of position, velocity, time

Examples of user equitment is the GPS reciever

Trilateration

Essentially the system works by creating a bubble around the satellites that is the psuedo range and the location of the intersection of those bubbles is where you are. With just one sat it knows the distance you are from the sat but not which point on the bubble

Reciever uses trilateration between 3 sats to determine 2D position (lat and long)

4 sats are used to determine 3D position (lat long and altitude), 4 sat gives altitude

How does the GPS compute information like speed and course?

By looking at the position changes as the intersection of the bubbles changes

What can the reciever give you?

Where you are

Where you are going

How long you’ve been traveling

How fast you’re going

ETA

GPS Operation

Sats constantly emit a signal to receivers

Location determined in time when signal was sent and recieved

Each sat and receiver has atomic clock, time information from sat is transmitted to the receiver.

Receiver compiles data to get distance.

How do GPS units navigate?

Great circle navigation - They determine the shortest distance between two points on a sphere

GPS CDI deflection shows distance off course in NM vs VOR CDI which should angular distance off course in degrees

GPS can substitute ADF or DME as long as GPS can be used in an NDB approach with the precense of “Or GPS in the title”

RAIM

A function of GPS recievers that monitors the integrity of the satellite signal. Without RAIM you have no assurance to the accuracy of the signal from the sats

RAIM (fault detection) requires 5 sats or 4 with baro aiding reciever

RAIM (fault exclusion) to remove a corrupt signal requires 6 sats or 5 with baro aiding

When is a RAIM error message given?

Sat position

Atomic clock malfunction

Not enough sats to compute RAIM

What are the types of GPS Augmentation systems?

GPS augmentation system - Improves accuarcy of GPS by recieving error from reference stations and broadcasting the errors to supported GPS receivers

SBAS - The parent system of WAAS (known as WAAS in the US)

• WAAS covers a wide area

GBAS - Also like WAAS but errors are broadcasted via VHF to GBAS enabled recievers

• Ground based augmentation system formally LAAS (local area)

• GBAS is more accurate than WAAS but covers a much smaller geographical area

• Allows for Cat I and above approaches to GLS DA minima

WAAS (fault detection w/correction)

WAAS improves accuracy, integrity, and availability of GPS signals

WAAS improves accuracy by determining errors from GPS satellites via ground based reference stations

Learn this WAAS diagram

Learn this WAAS diagram

What are the components of WAAS?

Geosynchronous sats (constellation)
Geostationary sats (3 total)
Wide area reference stations (38 total)
Wide area master stations (3 of those)
Geo uplink station (6)
WAAS GPS reciever (in a/c)

What is the reason for the biggest errors in signals?

Ionosphere delay is the reason for the biggest error in signals and is caused by the atmosphere altering the speed and direction of signal

What are some of the benefits of WAAS?

Improved accuracy and integrity of the signal

More extensive service area

Lower minimums for GPS approaches

• LP/LPV approaches for WAAS

• LNAV/VNAV approaches for RAIM

No need to check RAIM (unless issued to NOTAM)

Flight applicability of GPS

1) Have an approved GPS receiver

• If using GPS as primary means of NAV

  • Non WAAS receiver means you need another form of navigation

2) Current GPS database (28 days)

3) Check GPS NOTAMs before flight and use the RAIM prediction if avaliable on your reciever

4) Be familiar with GPS sensitivites

• Enroute more than 30NM from airport

  • Non WAAS ± 5NM

  • WAAS ± 2NN

• Terminal within 30NM

  • ± 1 NM

• Just before FAF (approach mode)

  • ± 0.3 NM

• (LPV ONLY) At Threshold

  • ± 350ft