Navigation Aids

Question 1

What are Wide Area & Local Area DGPS?

Answer 1

Wide: Info gathered by stations 500+ miles apart, central station collates and calculates corrections, corrections are sent to geostationary orbits.
Local: Info gathered by local ground stations, ground station transmits corrections via LOS VHF datalink.

Question 2

Describe a Non-Directional Beacon (NDB).

Answer 2

Surface wave, polarised - magnetic plane parallel to the ground.
A single loop antenna will predict two nulls (think a figure of 8, the middle bit is zero and thus you get to points of null).
By also using a dipole you get one (think half circle, half figure of eight).

Question 3

Describe an VOR (VHF omni-range antenna).

Answer 3

Uses VHF, is a space wave antenna.
Two signals are transmitted: Omni-directional reference signal, and a directional signal (rotates around azimuth at 30Hz). Phase difference of the two signals tells the receiver which VOR line they are on.
Range: 1.23* (sqr(Htransmitter) + sqr(Hreciever))

Question 4

Describe DME.

Answer 4

Distance Measuring Equipment.
Aircraft emits a pulse pair with random spacing, the DME responds on F-63Hz allowing an almost infinite number of aircraft to use the system. Time between transmission and response gives range.

Question 5

Purpose of differential GPS otherwise known as GPS augmentation.

Answer 5

Reduces the error of GPS derived positions using reference receivers which are receivers at known (usually fixed) locations.

Question 6

What is ILS?

What landing categories does it support?

Answer 6

Instrument Landing System
Uses radio frequencies to guide planes to runway.
Cat I down to 200ft and when used with auto land system, all Cat approaches.