飛行課程 Stage 3 - GPS Navigation
Contents:
GPS Overview
GPS Airborn Equipment
GPS Basic Navigation Considerations
GPS Pretakeoff Navigation Preparations
GPS Inflight Navigation Tasks
1. GPS Overview
GPS (Global Positioning System):
Satellite-based radio positioning and navigation system
Broadcasts signals that are used by GPS receivers to determine a precise, three-dimensional position anywhere in the world
It can calculate course, bearing, and distance to any latitude and longitude coordinate on earth
Aviation GPS receivers contain a database that stores retrievable navigation data, such as airport and navaid information and airway intersections
The Number of Satellites
Minimum of 24 satellites
Comprises six orbital planes with four equally spaced satellites in each plane - provide complete pole-to-pole coverage at all times
Three-Dimensional Position
Aircraft position is calculated by measuring the time a signal from each satellite takes to reach the GPS receiver
A three-dimensional position solution is important because the GPS altitude data is used for all calculations that require aircraft altitude, such as terrain awareness
Only latitude and longitude (only three satellites are in view) is acceptable for only VFR navigation
GPS NOTAMs????
The FAA issues GPS NOTAMs to inform you of:
Knowledge outages cause by satellite failures
Scheduled outages due to maintenance
In online briefings, the NOTAM is contained in a special GPS section of the text. In verbal briefings, the section is identified verbally
Ask for GPS NOTAMs if they are not included in your briefing. Your receiver might not automatically indicate that the GPS signals have degraded or that they are not available
RAIM and Fault Detectioin and Exclusion
Receiver Autonomous Integrity Monitoring (RAIM):
Monitors the integrity of GPS signals
Provides notification when signal integrity drops below acceptable levels or there are not nough satellites in view
Enhanced version of RAIM can include fault detection and exclusion (FDE), which:
Detects faulty satellites and then automatically excludes them from the position calculation
Enables the receiver to continue GPS navigation without interruption if enough satellites are in view
GPS Accuracy
Can be expressed as plus or minus 50 feet
Factors for accuracy:
exactness of time in the calculation
orbital errors
atmospheric effects
signal reflections
satellite geometry
?WAAS and LAAS
Wide Area Augmentation System (WAAS)
Reduce errors in the position calcuation
Receive information indicating areas in which the GPS system is unusable
Exclude faulty signals within seconds of a satellite failure or error
Receive the WAAS signals over a wide area, such as over several states
Local Area Augmentation System (LAAS)? ? ? ?
It yields greater accuracy than WAAS
It computes and broadcasts a higly accurate correction message on a VHF radio and provides high levels of accuracy, availability, and integrity over a more limited or local area of 20 to 30 miles from the airport??? ? ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
2. GPS Airborn Equipment
GPS Receiver:
Handheld units - typically VFR only
Panel-mounted unites - installed in the instrument panel and are powered by the aircraft
Integrated system - integrate GPS functionality with other systems such as primary flight instruments, communication, and navigation radios
GPS receivers used in a flight management system (FMS) - GPS position information serves as one of many inputs in determining aircraft position
Integrated Electronic Flight Displays
The primary flight display (PFD)? ?
HSI - capable of displaying GPS lateral-course-deviation information in a way that is similar to how a traditional HSI shows VOR course deviation
On the PFD:
The HSI indicates the lateral distance you are off course, not the number of degrees you are off course
The HSI displays GPS navigation in three different modes. The three differ in the scale they use to show lateral deviation. As you change GPS course-information modes, the course-deviation scale on the HSI changes. When you use the HSI to determine how far off course you are, it is critical that you are aware of which particular GPS-navigation mode you are in
The multifunction display (MFD)
A visual indication of your position relative to your desired course, along with a representation of your track
Navigation aids, airports, airspace, intersections, and VFR waypoint overlays on the map
Terrain information in conjunction with a terrain awareness warning system (TAWS)
A topographical depiction of the terrain below your aircraft, similar to a sectional chart
Obstacle data in conjunction with TAWS
Nearly real-time weather information and NEXRAD information overlays
3. GPS Basic Navigation Considerations
VFR Waypoints for GPS
Waypoints:
Used in navigation to previde guidance so that you can fly the aircraft to a specific point over the earth
Predefined, in many cases with a name and latitude and longitude coordinates, but you can also create them
Retrievable from a navigation database by a GPS receiver if they are predefined
VFR Waypoints:?
Published on aeronautical charts
Identifer consist of five letters beginning with "VP"
VFR waypoints can be standalone, or they can be collocated with VFR checkpoints and VFR reporting points
They can be used to support the preferred flow of traffic in the vicinity of an airport
ATC does not know VFR waypoints unless these waypoints are collocated with a VFR checkpoint or VFR reporting point
GPS is TO-TO Navigation
GPS navigation is To-To navigation using waypoints and waypoint sequencing rather than traditional VOR TO-FROM navigation
GPS Routes
For GPS navigation, a route is a series of waypoints
Often called the desired track
The computed desired track is almost always more accurate
When you navigate along your route, the desired track between your previous waypoint and the waypoint ou are navigating to is the active leg. All of the guidance information your GPS provides is absed on the active leg
Track, Desired Track, and Cross-Track Error
Track, displayed as a vector on the MFD's moving map, is the direction in which the aircraft is currently moving over the ground, regardless of the aircraft's heading
When the track value is equal to the desired track value, you are either on the desired track or parallel to it
Cross-track error is the distance measured in nautical miles between the aircraft and the desired track
When the aircraft is flying on the desired track, the desired track (DTK) and track (TRK) are equal and the cross-track error (XTK) equals zero nautical miles
Track Angle Error
Track angle error (TKE) value is equal to the difference between the track (TRK) and the desired track (DTK) value
Out-of-Date Database
If GPS database is out of date:
Must not rely on the moving map for critical navigation decisions
Must verify named waypoint locations when navigating to a named fix, and you must verify waypoint coordinates with current and approved navigation information
4. GPS Pretakeoff Navigation Preparations
Pretakeoff Navigation Procedures
Initialize the GPS and perform any data-input tasks during preflight preparations
GPS Initialization and Setup
The fundamental elements of GPS initialization and setup typically include:
Determining through a system self-test whether the GPS receiver is capable of performing navigation
Initializing the system software
Verifying the effective datas of the installed GPS database
Verifying the internal software versions and airframe-specific installation versions
Verifying satellite reception and signal quality
The GPS Flight Plan Function
A typical GPS flight plan function enables you to:
Enter your intended waypoints in the order in which you intend to fly them
View flight information as it is calculated and displayed by the system for each leg of the flight plan. Cumulative information for the route is available during the entire flight
View database information according to the specific of your route
Compare total distance of the route with distance remaining; this information is continuously updated in real time
Pretaxi Preparations:
Input or select and ativate your flight plan verify the flight plan route waypoint by waypoint, and ensure that the waypoint identifiers are correct
Verify that an active leg is indicated on the flight plan and that the active leg is the first leg you want to fly
Set up the VOR navgation radios with the ppropirate navigation frequencies and cross radials if you plan to cross check your position using VORs along your route
Note the orientation of the departure runway relative to the active leg so that you can determine how best to intercept the course
Before you begin to taxi, set a map scale on the MFD that allows you to maintain awareness of your location at the airport relative to the runways
Complete as much GPS and avionics programming as possible while on the ground with the parking brake set
5. GPS Inflight Navigation Tasks
Orienting the Aircraft Relative to the Active Leg
Maneuvering to Intercept the Active Leg
Intercepting the Active Leg
Maintaining Your Position on the Active Leg
Orienting the Aircraft to the Arrival Airport
