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VOR Navigation AST 241 Chapter 2

VOR Navigation

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  • VOR NavigationAST 241Chapter 2

  • HistoryVORs derived from the old 4-course radio range from the late 1920s and 1930sGained widespread use for navigation in the 1950sMade instrument navigation commonplaceRemain the basis for most of the worlds air navigation systems- and will be for 5-10 yrs.

  • Principles of operationVORs are commonly described as broadcasting 360 separate radials emanating from the station in all directions.How do they really work?VORs broadcast 2 signals- the reference (or 360-N) signal and the rotating signal.

  • Principles of OperationIf the two signals are in phase the aircraft is on the 360 radial, if the receiver detects these signals are out of phase by then the aircraft is located on the 90 radial from the station and so on.

  • Principles of operationRemember the VOR Omni head in the aircraft only tells the pilot one thing which is?Where the aircraft is located with respect to the selected radial- IF interpreted correctly.No aircraft heading information (unless HIS)No distance information

  • Principles of operationWhat is the most important initial action when using a VOR for air navigation?Tune and IDENTIFY the Station

  • VOR informationHow is a VOR used to Determine which radial an aircraft is located on?How is a VOR used to determine a heading to get to a particular station?How Can the VOR receiver(s) be used to locate your relative position if lost?

  • VOR informationMost pilots are taught to use the VOR as a command instrument- Which way do I fly?The VOR receiver was originally designed as a SHI- Station Heading Indicator.

  • SHI Steps:Tune and identify the stationPut the desired radial at the top of the indicator and interpret where you are in relation to that selected course.Use the CDI (course deviation indicator) and the TO/FROM flag to divide the VOR into quadrants.The midpoint of the quadrant containing the CDI and the TO/FROM flag will give a 45 degree INBOUND intercept for the selected course.

  • SHI steps ctn.The midpoint of the quadrant with the CDI but opposite the TO/FROM flag will give a 45 degree OUTBOUND interceptREMEMBER- if after that you plan to track TO the station to orient the OMNI Head so that your aircraft heading and VOR indication are the same to avoid reverse sensing- Have a TO indication if going TO the station.

  • TrackingAll previous principles work well in a no-wind situationWind complicates the process in 3 ways:The greater the distance from the station the slower the needle reacts (Fig. 2-11)The stronger the cross-wind the greater the correction should beThe faster the aircraft the less the correction should be- less relative effect on the aircraft

  • Tracking2 Basic means of establishing track:Bracketing and EstimatingBracketing- logical trial & ErrorThe speed of needle drift is an indirect indication of the crosswind strength

  • TrackingThe 30 degree rule for tracking:Make a 30 degree initial turn toward the needle (assuming correct orientation)When the needle centers- remove of the correction- 7-8 degrees.Watch needleIf it drifts back in the direction of the original drift- add the 7-8 removed degrees back in and go 7-8 in the other direction

  • TrackingIf the needle drifts the other way take 8 degrees out.Go through this iteration again using 3-4 degrees and then again with 1-2 degrees until a workable heading is found*Then the wind will change!

  • EstimatingEstimating is essentially the same as tracking except you start with a pre-calculated value based on known wind information.When using this method begin with 5 degree changes instead of the 15 degrees used when winds are not known.- this is generally a quicker method.

  • VOR testingHow often do VOR receivers have to be tested for tolerance for VFR flight?How about for IFR flight?Every 30 days- with a logbook entry give date, time/place, name & bearing error.Many airports have VOT faciltiesWhat are they and how do you know if they have one?

  • TestingWhat is the allowable error if using a VOT?+/- 4 degreesWhat are the acceptable VOR indications when using a VOT?180-TO and 360- FromSome airports have certified VOR checkpoints on the field- refer the the AFD.

  • TestingWhen using checkpoints what are the allowable tolerances?Ground +/- 4 degreesFlight +/- 6 degreesYou are allowed to make your own checkpointsIf tested against each other 2 receivers must be within ______ degrees?4 degrees

  • TestingIt is recommended that VORs be periodically calibrated as they may indicate correctly close to the station yet be out of tolerance when at a greater distance.

  • VOR rangeThe VOR transmission is limited to line of sight and can be disrupted by terrain- to avoid this stay on published airways or refer to the AFDRemember the VOR accuracy is limited to 1 degree which may add up to a 28 mile discrepancy at 200 miles if the VOR is at the 4 degree max. tolerance.

  • VOR rangeTerminal VOR (T)- from 1,000 ft. to 12,000 ft. out to 25 NMLow Alt. (L)- from 1,000 ft. to 18,000 ft out to 40 NMHigh Alt.(H)- from 1,000 ft. 14,500 out to 40 NM, from 14,500ft. 60,000 ft. out to 100 NM and from 18,000 ft. - 45,000 ft. out to 130 NM.

  • The End