Transcript Document 7315231

VOR Navigation
AST 241
Chapter 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 precalculated 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