VOR Navigation
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Transcript of VOR Navigation
VOR Navigation
AST 241Chapter 2
History
• VOR’s derived from the old 4-course radio range from the late 1920’s and 1930’s
• Gained widespread use for navigation in the 1950’s
• Made instrument navigation commonplace• Remain the basis for most of the world’s air
navigation systems- and will be for 5-10 yrs.
Principles of operation
• VOR’s are commonly described as broadcasting 360 separate radials emanating from the station in all directions.
• How do they really work?• VOR’s broadcast 2 signals- the reference
(or 360-N) signal and the rotating signal.
Principles of Operation
• If the two signals are in phase the aircraft is on the 360 “radial”, if the receiver detects these signals are out of phase by ¼ then the aircraft is located on the 90 “radial” from the station and so on.
Principles of operation
• Remember 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 operation
• What is the most important initial action when using a VOR for air navigation?
• Tune and IDENTIFY the Station
VOR information
• How 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 information
• Most 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 station• Put 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 intercept
• REMEMBER- 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.
Tracking
• All previous principles work well in a no-wind situation
• Wind 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 be• The faster the aircraft the less the correction
should be- less “relative” effect on the aircraft
Tracking
• 2 Basic means of establishing track:• Bracketing and Estimating• Bracketing- logical trial & Error• The speed of needle drift is an indirect
indication of the crosswind strength
Tracking
• The 30 degree rule for tracking:• Make a 30 degree initial turn toward the needle
(assuming correct orientation)• When the needle centers- remove ½ of the
correction- 7-8 degrees.• Watch needle• If 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
Tracking
• If 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!
Estimating
• Estimating 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 testing
• How 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 facilties• What are they and how do you know if they
have one?
Testing
• What is the allowable error if using a VOT?• +/- 4 degrees• What are the acceptable VOR indications
when using a VOT?• 180-TO and 360- From• Some airports have certified VOR
checkpoints on the field- refer the the AFD.
Testing
• When using checkpoints what are the allowable tolerances?
• Ground +/- 4 degrees• Flight +/- 6 degrees• You are allowed to make your own checkpoints• If tested against each other 2 receivers must be
within ______ degrees?• 4 degrees
Testing
• It is recommended that VOR’s be periodically calibrated as they may indicate correctly close to the station yet be out of tolerance when at a greater distance.
VOR range
• The 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 AFD
• Remember 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 range
• Terminal VOR (T)- from 1,000 ft. to 12,000 ft. out to 25 NM
• Low Alt. (L)- from 1,000 ft. to 18,000 ft out to 40 NM
• High 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