GPS - ATP Flight School Flashcards
ATPFlightSchool.com
What is GPS?
Global Positioning System, a satellite-based radio navigation system.
ATPFlightSchool.com
What is RNAV?
Area navigation, a system that gives electronic course guidance on a direct route between any two points (rather than just between ground-based navaids). GPS is a type of RNAV.
ATPFlightSchool.com
What is RAIM?
Receiver autonomous integrity monitoring, a feature built into GPS receivers that detects and warns the pilot when a GPS satellite may be providing incorrect information.
ATPFlightSchool.com
What is baro-aided GPS?
A GPS system that uses a barometric (pressure-sensing) altimeter to refine the position solution obtained from satellite signals.
ATPFlightSchool.com
How many GPS satellites are there?
Currently (April 2016) there are 31 active GPS satellites on orbit. The baseline “constellation” includes 24 satellites, but the US Air Force has added additional satellites for better coverage.
ATPFlightSchool.com
How many GPS satellites need to be in view of a GPS receiver for it to work?
- To determine an accurate 3-dimensional position: 4
- To have RAIM functionality that detects faulty signals: 5
- To exclude the faulty signal: 6
ATPFlightSchool.com
Can a GPS satellite get “overloaded” if too many receivers try to use it?
No. Communication between GPS satellites and receivers is one-way, from the satellite to the receiver. The receiver does not transmit anything.
ATPFlightSchool.com
What information is transmitted in the GPS signal?
- The time the signal was sent
- The position of the satellite
- The satellite’s “health”/status
ATPFlightSchool.com
How does a GPS receiver determine its position?
GPS signals (like all radio signals) travel at the speed of light. By taking the difference between the times the signal was sent and received, and multiplying by the speed of light, the GPS receiver determines the distance to that satellite. Once the receiver calculates the distance to multiple satellites at known positions, it can triangulate its position.
ATPFlightSchool.com
Why does it take four satellite signals to calculate your position in three dimensions?
The GPS receiver has to solve for a fourth unknown - the error in the receiver’s clock, which isn’t perfectly synchronized with the atomic clocks in the satellites. (If you had an atomic clock in the receiver, you would only need 3 satellites, but a GPS receiver would be much more expensive!)
ATPFlightSchool.com
Do you have to have a current database to use a GPS for VFR navigation?
No, but you shouldn’t rely on the GPS to make critical navigation decisions if the database is out of date. Cross-reference with pilotage and dead reckoning to ensure the waypoints you use are where you expect them to be.
ATPFlightSchool.com
What are some factors to consider when using a hand-held GPS for VFR navigation?
- Depending on the receiver’s position inside the aircraft, it may lose signal in certain aircraft orientations.
- Handheld GPS units generally do not have RAIM capability.
- Any modification to the aircraft (like a yoke- or panel-mounted holder) is governed by 14 CFR Part 43.
ATPFlightSchool.com
When is the best time to enter waypoints into a GPS receiver?
Before the flight, while on the ground and stationary.
ATPFlightSchool.com
What standard of accuracy or integrity is required for VFR GPS units?
None - only IFR-certified GPS units have to meet regulatory standards.
ATPFlightSchool.com
How can you tell whether a waypoint in a GPS database is a VFR waypoint?
Its five-letter code begins with VP.
