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RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 1 VOR OPERATIONS Aim: To learn the principles behind the operation of the VOR navigation system. Application: - orientation (where am I?) - supplementary navigation information - IFR instrument approaches Definitions: VOR - VHF Omni-directional Radio Range Radial - is a magnetic track emitted FROM a VOR station. There are 360 of them, hence omni. Principles: operates on frequencies between 112.1 and 117.9MHz (VHF radio band - line of sight transmissions) Ground Station - transmits two VHF signals: The reference phase signal, which is omni-directional (ie: same in all directions) The variable phase signal, which rotates uniformly at a rate of 1800RPM, with its phase varying at a constant rate throughout the 360 Two signals transmitted are: - in phase at magnetic North - 90 out of phase at magnetic East - 180 out of phase at South - 270 out of phase at magnetic West - 360 out of phase (back in phase) at magnetic North RMIT Flight Training VOR Operations Brief 19 RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 2 - morse code identifier signal is transmitted every 10sec at 1020MHz, allowing positive identification of station. - since VHF signals are line of sight, range depends upon altitude. Rated coverage found in AIP GEN. Altitude (ft) Range (Nm) < 5000 60 5000 to 10000 90 10000 to 15000 120 15000 to 20000 150 > 20000 180 - details found in ERSA and ERC. Airborne Equipment - consists of three main components: Antenna - usually a twin blade, V-shaped antenna mounted on horizontal tail Reciever - the reciever and associated control panel are used to tune VOR and ILS stations. Usually combined with a VHF-COM set Indicator - Indication is regardless of HDG Brief 19 RMIT Flight Training VOR Operations RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 3 Considerations: Limitations - various limitations effect the readings of the VOR: a) Vertical Polarization - VOR stations emit radio waves, which are orientated horizontally. ie: waves oscillate parallel to Earth’s surface. Detected by horizontal antenna. When aircraft banks, antenna no longer horizontal and picks up errors. b) Terrain Effect - bearing information contained in VOR signals may be spurious signals reflected from terrain. This interference causes oscillations on the CDI. Rapid oscillations is scalloping. Slow oscillations known as course bending. c) Airborne Equipment - bearing errors arising from imperfections in indicator. d) Ground Site - signal accuracy is affected by ground station equipment (transmitter, aerial, etc). e) Site Effect - propagation of VHF signals is affected by physical obstacles or irregular terrain features near the VOR site. Minimised using Doppler VOR. f) Aggregate Error - algebraic sum of all errors mentioned. Rarely exceeds 5 Station Passage - passage overhead a VOR station is indicated by; needle becoming more and more sensitive, and oscillating; red, unserviceable flag appearing; TO flag becomes FROM flag; then needle becomes more stable as station departs. Brief 19 RMIT Flight Training VOR Operations RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 4 Air Exercise: T - Tune to VOR using reciever I - Identify using Morse code T - Test by rotating OBS through 360 Airmanship: - Always use VOR within its rated coverage - TIT checks before use - Always use as a “command instrument.” Brief 19 RMIT Flight Training VAODRFOInpteerracteiopntss |
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