ppl_03_e2
.pdf
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 17: VHF OMNI-DIRECTIONAL RANGE (VOR) QUESTIONS
7.What is the normal maximum aggregate error of a VOR system ignoring pilot error?
a.+/- 2°
b.+/- 5°
c.+/- 1°
d.+/- 3°
8.Which of the following instruments cannot incorporate VOR indications?
a.Horizontal Situation Indicator
b.Radio Magnetic Indicator
c.Direction Indicator
d.Omni Bearing Indicator
9.What is the function of the Course Deviation Indicator in a VOR OBI?
a.To point in the direction of the VOR beacon
b.To select the desired VOR radial on the OBI
c.To indicate an aircraft’s angular deviation from a selected VOR radial
d.To align itself with Magnetic North when synchronized with the compass
10.When the OBI is correctly set up under certain circumstances, the CDI acts as a ‘demand indicator.’ What does this mean, and what are the circumstances?
a.When the aircraft is heading in approximately the direction of the track selected on the OBI, if the CDI is to the left of centre it is indicating to the pilot to turn right to intercept the selected track, and if it is to the right of centre it indicates to the pilot that he should turn left to regain the selected track
b.When the aircraft is heading in approximately the reciprocal direction of the track selected on the OBI, if the CDI is to the left of centre it is indicating to the pilot to turn left to intercept the selected track, and if it is to the right of centre it indicates to the pilot that he should turn right to regain the selected track
c.When the aircraft is heading at approximately 90° to the direction of the track selected on the OBI, if the CDI is to the left of centre it is indicating to the pilot to turn right to intercept the selected track, and if it is to the right of centre it indicates to the pilot that he should turn left to regain the selected track
d.When the aircraft is heading in approximately the direction of the track selected on the OBI, if the CDI is to the left of centre it is indicating to the pilot to turn left to intercept the selected track, and if it is to the right of centre it indicates to the pilot that he should turn right to regain the selected track
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Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 17: VHF OMNI-DIRECTIONAL RANGE (VOR) QUESTIONS
11.When will an OBI indicate FROM?
a.When the radial selected on the OBI is equal to, or approximately equal to, the aircraft’s heading, and that heading will take the aircraft away from the VOR beacon
b.When the radial selected on the OBI is equal to, or approximately equal to, the reciprocal of the aircraft’s heading, and that heading will take the aircraft away from the VOR beacon
c.When the radial selected on the OBI is equal to, or approximately equal to, the aircraft’s heading, and that heading will take the aircraft towards the VOR beacon
d.When the radial selected on the OBI is equal to, or approximately equal to, the reciprocal of the aircraft’s heading, and that heading will take the aircraft towards the VOR beacon
12.When will an OBI indicate TO?
a.When the radial selected on the OBI is equal to, or approximately equal to, the aircraft’s heading, and that heading will take the aircraft away from the VOR beacon
b.When the radial selected on the OBI is equal to, or approximately equal to, the reciprocal of the aircraft’s heading, and that heading will take the aircraft away from the VOR beacon
c.When the radial selected on the OBI is equal to, or approximately equal to, the aircraft’s heading, and that heading will take the aircraft towards the VOR beacon
d.When the radial selected on the OBI is equal to, or approximately equal to, the reciprocal of the aircraft’s heading, and that heading will take the aircraft towards the VOR beacon
13.A pilot is instructed to track inbound to a VOR beacon on the 120° Radial. What track will he select on the OBI in order that he can use the OBI to intercept that radial, with the TO flag showing, and what heading will he fly along the radial, assuming no wind?
a.120° and 120° Magnetic
b.120° and 300° Magnetic
c.300° and 300° Magnetic
d.300° and 120° Magnetic
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ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 17: VHF OMNI-DIRECTIONAL RANGE (VOR) QUESTIONS
14.A pilot is instructed to track outbound from a VOR beacon on the 270° Radial. What track will he select on the OBI in order that he can use the OBI to intercept that radial, with the FROM flag showing, and what heading will he fly along the radial, assuming no wind?
a.270° and 270° Magnetic
b.090° and 270° Magnetic
c.270° and 090° Magnetic
d.090° and 090° Magnetic
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Question 12 13 14
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The answers to these questions can be found at the end of this book.
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 18
DISTANCE MEASURING EQUIPMENT (DME)
331
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 18: DISTANCE MEASURING EQUIPMENT (DME)
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ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 18: DISTANCE MEASURING EQUIPMENT (DME)
INTRODUCTION.
You have learned that a pilot may fix his position by taking bearings from two NDBs, two VOR beacons, or from an NDB and a VOR beacon. However, for the pilotnavigator, operating alone, such a procedure is inconvenient. Nowadays, though, most VOR beacons are co-located with a second radio-navigation device called
Distance Measuring Equipment (DME). DME also operates through 360º and enables the pilot to establish the distance of his aircraft from the VOR/DME beacon along any selected radial, so that he can fix his position precisely. The DME itself works on the secondary radar principle, and the equipment fitted to the aircraft is an interrogator which measures the time taken by signals to travel from the aircraft to the beacon and back again, in order to measure range.
Figure 18.1 Aircraft DME Display and Controls.
As well as giving the distance from the beacon, the DME display in the aircraft may also show an aircraft’s groundspeed and the time required to arrive overhead the beacon. The groundspeed shown is meaningful only when the aircraft is tracking directly to or from the station, and the time required readout is only meaningful when the aircraft is tracking directly to the station, since the equipment calculates groundspeed and time from the rate of change of distance..
OBTAINING AN ACCURATE POSITION FIX.
By selecting a desired radial from a VOR beacon and reading distance from a colocated DME, the pilot obtains an accurate fix, giving him his exact position.
Figure 18.2, overleaf, shows an aircraft approaching a VOR/DME beacon on the 180º radial. As the pilot is tracking to the beacon, he has selected the reciprocal radial, 000º, on his OBI, and so the TO flag is showing.
The pilot can read from his DME display that the distance of his aircraft from the VOR/DME beacon is 15 nautical miles (nm), that his groundspeed is 120 kts and that the time required to reach the station is 7.5 minutes.
The radial on which an aircraft is positioned relative to the VOR/DME beacon is in degrees magnetic, so as the compass rose around the beacon is aligned on Magnetic North, the radial can easily be drawn or estimated by eye. On the
The
groundspeed shown is only
meaningful
when the aircraft is tracking directly to or from the station, and the time required readout is only meaningful when the aircraft is tracking directly to the station.
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Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 18: DISTANCE MEASURING EQUIPMENT (DME)
1:500 000 aeronautical chart, one inch is about 7 nautical miles and the average distance between the knuckle of the thumb and the tip of the thumb is about 10 nm, while a hand span is about 55 nm. So, with or without a rule, distance along a radial can be estimated on the chart to confirm a ground position.
An aircraft’s position can
be established by identifying
the intersection of two DME circular position lines, provided ambiguity is resolved.
A DME “position
line” is the circumference
of a circle, the centre of which is the DME beacon.
Figure 18.2 DME Position Fix.
If the on-board DME display has no groundspeed readout, an aircraft’s groundspeed can, nevertheless, be easily calculated when flying directly to or from a VOR/DME beacon. The pilot simply times the interval between two DME range readings and carries out a mental calculation.
For example if, in the time of 1 min, the aircraft has travelled 1.5 nm directly towards the beacon the groundspeed of the aircraft will be 60 x 1.5 = 90 knots.
Figure 18.3 Determining position by taking two DME range readings.
Because the DME read-out in the cockpit indicates distance from the ground station, but not direction, a DME position line is the circumference of a circle, the centre of which is the DME beacon. (See Figure 18.3.) When en-route, therefore, a pilot can obtain a reasonably accurate position fix by ascertaining the range of his aircraft from 2 separate DME stations. The aircraft’s position is at the intersection of the two circles. Note, however, that the circles will usually intersect at two points, giving rise to an ambiguity which must be resolved by a third position line, particularly if both DMEs are on or near the aircraft’s fore and aft axis.
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ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 18: DISTANCE MEASURING EQUIPMENT (DME)
DME ARCS LEADING TO AN INSTRUMENT APPROACH.
The curved path of a DME arc is often used as a transitional path from the en-route phase of a flight to an instrument approach procedure.
DME can also be paired with centreline localisers in instrument landing systems (ILS), so that a pilot knows his distance from touch down.
DME OPERATING FREQUENCIES.
DME operating frequencies fall within the UHF range of 962 - 1213 MHz. However, these frequencies are not directly selectable. The DME control unit in the DME receiver has an associated VHF frequency selector and the DME frequency is paired with the co-located VOR beacon’s VHF frequency.
SLANT RANGE CONSIDERATIONS.
DME measures the slant distance of an aircraft from the ground station. Though the slant distance from a beacon is slightly greater than the horizontal distance, in practice the distances are close enough for the purpose of navigation. For instance, an aircraft at 3000 feet and a horizontal distance of 15 nm from a DME beacon would subtend an angle of only 2º at the DME station. At this angle, the slant distance between the aircraft and the beacon would be 15.01 nm. The difference between the horizontal and slant distances would, therefore, be only 0.01 nm.
When the aircraft in Figure 18.4 is overhead the ground station, the horizontal distance will, of course, be zero, although the DME display will indicate about 0.5 nm. While the position overhead the beacon is the position of greatest error, 0.5 nm is a negligible value and can be ignored. The groundspeed indication, however, will reduce to a very low figure in the overhead, so is unreliable within a couple of miles of the overhead.
DME
measures the slant distance
of an aircraft
from the ground station. For practical navigation purposes, the difference between slant range and
horizontal range is negligible.
Figure 18.4 For practical, navigation purposes, the difference between slant range and horizontal range is negligible.
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Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 18: DISTANCE MEASURING EQUIPMENT (DME)
DME transmissions are subject to the
line-of-sight rule.
DME is very accurate.The total system error should
be no more than +/- 0.2 nm for recently manufactured aircraft.
PRINCIPLE OF OPERATION.
Secondary Radar.
DME works on the secondary radar principle which is covered in Chapter 20. For the purpose of this chapter, it is sufficient for you to note that the DME ground station is equipped with a type of transponder which responds to interrogation signals from aircraft tuned to the DME beacon’s frequency.
An aircraft sends out an interrogating pulse, and the ground station responds by re-transmitting a strong answering signal which is received in the aircraft. The DME receiver on board the aircraft converts this signal, using simple speed and time formulae, into a digital readout of distance in nautical miles.
Range and Coverage.
DME transmissions are subject to the line-of-sight rule. Thus, the higher the aircraft and the ground station, the greater the theoretical reception range. The formula for calculating the maximum line-of-sight range is the same as that given for VHF signals from a VOR beacon, in Chapter 17.
Of course, if there is intervening high ground, in order to receive DME readings an aircraft will have to be at higher altitude than that suggested by the maximum range formula.
If we assume that the elevation of the DME beacon is negligible (i.e. near sea level) the range formula simplifies to:
DME range = 1.25 x aircraft altitude.
Range errors may also be caused by co-channel interference from 2 or more ground beacons having the same frequency. A designated operating area is published in the ENR section of the UK AIP for all DME stations within which co-channel interference is unlikely to be experienced.
Accuracy.
DME is very accurate. The total system error should be no more than +/- 0.2 nm for recently manufactured aircraft. For older aircraft, registered before 1 Jan 1989, the error is 0.25 nm + 1.25% of the range. Slant error is significant only when the aircraft’s range is less than 3 times its height above the beacon.
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