GPS

Question 1

Satellite System

Answer 1

21 satellites with 3 spares in 6 orbital planes at an angle of 55 degrees to the equator
Orbits once every 12 hours

Question 2

Ranging

Answer 2

Calculated position by measuring distance from satellites by timing travel of signals
Four satellites requires to correct for any slight timing errors for a 3D fix

Question 3

Timing

Answer 3

Receiver requires four channels for four satellites

Question 4

Pseudo-Random Code

Answer 4

Satellite and receiver generate the same signal at the same time to calculate the time taken for the signal to travel

Question 5

Errors

Answer 5

Satellite clock
Ephemeris (satellite positioning)
Ionosphere
Troposphere
Receiver
Selective Availability (not currently active)
GDOP/PDOP

Question 6

Availability

Answer 6

Ratio of total time a facility is operationally for use to the total time in a specified period

Question 7

Integrity

Answer 7

Ability of the system to provide warning that the system shouldn’t be used

Question 8

Receiver Autonomous Integrity Monitoring (RAIM)

Answer 8

Six satellites required for RAIM to continue following detection and deselection of faulty statellite
Requires five satellites to compare information without at satellite failure

Question 9

Baroaiding

Answer 9

Can assist RAIM
Aircraft barometric altitude information is supplied to the GPS acting as another satellite using the Earth’s surface as a ranging sphere
Reduces need of RAIM to 4 or 5 satellites respectively

Question 10

Differential GPS

Answer 10

Uses ground-based monitoring equipment to determine the any error in the GPS signal
Correction for the error is computed and relayed to the aircraft giving increased accuracy required for a precision approach

Question 11

Inertial Navigation System (INS)

Answer 11

Completely self contained single source for nav data
Being supplied with the initial position information it can update the aircraft position, ground speed, attitude and heading and provides information for the autopilot and flight instruments

Question 12

Triple INS

Answer 12

Three systems increasing nav accuracy as position outputs are compared and averaged
Triple mix position

Question 13

Strapped Down Laser Gyro Inertial Reference System (IRS)

Answer 13

Ring laser gyro (RLG) is an angular rate measurer
Inertial sensor is strapped to the aircraft fuselage and detects changes in attitude through the angular rate sensing capability of the RLG’s and velocity changes through accelerometers

Question 14

Benefits of IRS

Answer 14

No moving parts, increased mean time between failure, decreased electrical power and provides digital output to other aircraft systems
Also have the ability to DME update and Triple mix