ppl_03_e2
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 19: RADAR
DISADVANTAGES OF PRIMARY SURVEILLANCE RADAR SYSTEMS.
The main advantage of primary surveillance radar is its ability to give air traffic controllers information about aircraft in their area of watch, without any participation required from an aircraft’s equipment in order for it to be detected by the radar head. However, primary radar does have the following disadvantages.
•Primary radar transmitters need to operate at very high power in order that an effective return signal is obtained from the target aircraft, especially if the radar transmitter is part of a long-range, en-route surveillance radar system.
•With long-range radars, return signals may be weakened by changes in target aircraft attitude, or attenuated by heavy precipitation. Both of these phenomena may cause traces on the radar screen to fade.
•A primary radar which is powerful enough to detect returns from distant target aircraft may also detect and display returns from high ground and precipitation. These types of return produce “clutter” on the radar screen.
•With primary radar, matching a given radar trace to an individual aircraft requires the aircraft to participate in an identification manoeuvre.
This latter disadvantage of primary radar systems can be overcome by the use of secondary surveillance radar. Secondary surveillance radar is covered in the next
chapter.
LOWER AIRSPACE RADAR SERVICE (LARS).
The Lower Airspace Radar Service (LARS) was introduced in 1979 as a funding scheme to reimburse Air Navigation Service Providers for the provision of the radar service element of the Air Traffic Services Outside Controlled Airspace (ATSOCAS).
All traffic flying IFR in controlled airspace will generally be in receipt of a radar service. In the United Kingdom, aircraft flying VFR in uncontrolled airspace may also be able to receive a surveillance radar service when in receipt of a Traffic or Deconfliction Service as part of the UK FIS , although provision of a service is at the controller’s discretion, depending on primary workload. LARS forms an integral part of ATSOCAS.
A LARS is available from 29 participating Air Traffic Control Units, 15 of which are military and 14 of which are civil.
Participating aerodromes are depicted in Figure 19.8. Aerodromes offering a LARS are listed in the En-Route Section of the United Kingdom Aeronautical Information Publication (UK AIP).
Significant Features of LARS.
•LARS is available outside controlled airspace up to and including FL 95, within the limits of radar/radio cover.
•LARS is provided within approximately 30 nms of each participating aerodrome.
•LARS is normally available Mondays to Fridays between 0800 & 1700 hrs, in summer, and 0700 & 1600 hrs, in winter, although sometimes the service will be available outside these hours.
•While receiving a LARS, the pilot-in-command remains responsible for maintaining terrain clearance.
The only way that Primary Surveillance
Radar can positively identify a specific aircraft is for
the controller to instruct the aircraft to perform an identifying manoeuvre.
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CHAPTER 19: RADAR
•The controller providing a LARS will not be aware of all aircraft which are operating in the airspace in which the aircraft receiving the LARS is flying. Therefore, a sharp lookout should be maintained at all times by pilots receiving a LARS.
When the LARS controller and the pilot requesting a LARS have established contact, and the LARS has been confirmed, the pilot should:
•Maintain a listening watch on the allocated frequency.
•Follow advice issued by the controller or, if unable to do so, inform the controller.
•Advise the controller when the service is no longer required.
Fig 19.8 Air Traffic Control Units participating in LARS.
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CHAPTER 19: RADAR
RADAR SERVICES.
General.
As part of the UK Flight Information Service (FIS) a radar surveillance service may be provided in the form of a Traffic Service or Deconfliction Service. These services may be provided by Air Traffic Service Units (ATSUs) to aircraft outside controlled airspace (in classes F and G). The Lower Airspace Radar Service (LARS) forms an integral part of these services.
A pilot may ask for either a Deconfliction Service or a Traffic Service. If, however, the Radar Controller is busy, only Traffic Service may be offered. The pilot remains responsible for terrain clearance at all times whether receiving a Deconfliction Service or Traffic Service.
Difference between Deconfliction Service and Traffic Service.
Deconfliction Service.
In a Deconfliction Service, information about other traffic is passed to aircraft receiving the Deconfliction Service. Additionally, the controller passes advice on avoiding action to be taken by the pilot in the form of headings to be steered (radar vectors), and, if necessary, height changes. A Deconfliction Service is available to IFR flights whether in IMC or VMC, but should be accepted by a VFR pilot only if VMC can be maintained at all times in the event of any suggested heading or level changes.
Traffic Service.
In a Traffic Service, information about other traffic is passed to aircraft in receipt of the Traffic Service, but no advice is given on avoiding action to be taken. The pilot of the aircraft receiving the Traffic Service is responsible for his own separation. A Traffic
Service is available to all aircraft whether IFR or VFR, and in any meteorological conditions.
Should a VFR Pilot Request a Deconfliction Service or a Traffic Service?
UnlessapilotisqualifiedtoflyinIMCandisflyingIFR,heshouldacceptaDeconfliction Service only in conditions where compliance with ATC advice permits the flight to be continued in VMC. Bear in mind that you cannot fly VFR in any conditions other than
VMC.
Apilot requesting a Deconfliction Service or Traffic Service should adopt the following procedure, having first established contact with the radar controller:
•State whether he is flying IFR or VFR.
•Request either Deconfliction Service or Traffic Service. The radar controller will attempt to identify the aircraft and then confirm the type of service about to be provided.
•The pilot reads back the service offered.
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CHAPTER 19: RADAR QUESTIONS
Representative PPL - type questions to test your theoretical knowledge of Ground Radar.
1.En Route Surveillance Radars are:
a.Long range radars with typical ranges of 200 - 300 nms.
b.Radars providing positional information above 25 nms.
c.Radars with a range of 75 nms used for controlling traffic in a Terminal Area.
d.Radars providing surveillance below FL 245.
2.Consider the following statements concerning air traffic control primary surveillance radar, and then choose the combination of correct statements from the options given.
1.ATC primary surveillance radar (PSR) can provide radar vectoring to pilots to fit aircraft into a safe and effective landing sequence.
2.ATC PSR provides information to pilots about significant weather.
3.ATC PSR range depends on the elevation of the radar head and the altitude of the aircraft.
4.ATC PSR enables controllers to ensure safe separation between aircraft under their control.
5.ATC PSR enables radar controllers to provide basic information to pilots about the position and heading of other potentially conflicting traffic.
6.ATC PSR is a pilot-interpreted aid which enables aircraft to determine their position and heading with respect to radar beacons.
a.1, 3, 5 & 6
b.1, 3, 4 & 5
c.1, 2, 4 & 5
d.2, 3, 4 & 6
3.The issuing of instructions to pilots by radar controllers in order that aircraft may avoid conflicting traffic or be led into an instrument landing system is known as:
a.Primary Radar Surveillance
b.Secondary Radar Surveillance
c.Radar Vectoring
d.Radar Information Service
4.In the absence of a radar service, the process used by air traffic control units to maintain separation between aircraft, based on the reported position and altitude of participating aircraft, is known as:
a.radio separation
b.procedural separation
c.altitude separation
d.position separation
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 19: RADAR QUESTIONS
5.A radar approach service whereby the radar controller passes advice to the pilot on his position relative to centreline and glideslope is called:
a.Surveillance Radar Approach
b.Instrument Landing System
c.Procedural Approach
d.VOR approach
6.If an aircraft’s groundspeed is 100 knots, what rate of descent must a pilot fly in order to obtain a glideslope approach of approximately 3 degrees?
a.500 feet per minute
b.100 feet per minute
c.450 feet per minute
d.600 feet per minute
7.The approximate maximum range of a primary radar transmitter situated at mean sea level to detect aircraft flying at an altitude of 5000 feet is:
a.105 nautical miles
b.70 nautical miles
c.5000 nautical miles
d.90 nautical miles
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The answers to these questions can be found at the end of this book.
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CHAPTER 20
SECONDARY SURVEILLANCE
RADAR (SSR)
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CHAPTER 20: SECONDARY SURVEILLANCE RADAR
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 20: SECONDARY SURVEILLANCE RADAR
PRINCIPLES OF OPERATION OF SECONDARY SURVEILLANCE
RADAR.
You have learnt that one of the main advantages of Air Traffic Control Primary
Surveillance Radar (PSR) is that it does not rely on the target aircraft carrying any specialist equipment for effective radar surveillance to be carried out. Only a radio is needed for the pilot of an aircraft to be able to participate in a PSR radar control service.
PSR has one major disadvantage, however, which is closely related to its independence of operation, namely that, in order to identify a particular aircraft so that specific assistance or instructions may be given to that aircraft, a PSR controller is obliged to request or instruct that aircraft to carry out a manoeuvre, usually a change in heading, which can be seen and recognised from the aircraft’s trace on the radar screen.
This disadvantage is overcome by Secondary Surveillance Radar systems.
Secondary Surveillance Radar grew out of the World War 2 Identification Friend or
Foe (IFF) system. IFF depended on dedicated receiver/transmitter units located in aircraft which responded to coded radar interrogations signals, retransmitting coded replies to indicate that the aircraft was not an enemy machine.
Nowadays, Secondary Surveillance Radar (SSR) functions alongside Primary Surveillance radar (PSR) and enhances the performance of PSR. With SSR, on every sweep of the radar head, a second, high-frequency interrogation signal is emitted along with the primary radar signal. An aircraft fitted with airborne SSR equipment, known as a transponder (a contraction of ‘transmitter-responder’), receives the signal and in response to the interrogation emits in return, its own coded signal, which not only enhances the clarity of the radar trace but also carries within the coded signal additional information such as an identification code, or altitude and speed read-out, which is received at the ground station and displayed on the radar screen.
SSR, then, enables the air traffic controller to identify an individual aircraft without any identifying manoeuvre having to be performed by the target aircraft, though the pilot does have to select a code on his transponder, assigned by the controller.
The enhanced intensity of the SSR radar trace can also eliminate radar returns from unwanted sources, such as terrain, and, thus, reduce clutter on the radar screen.
SSR transmissions, being one-way only, in order to key a response from the aircraft’s transponder, require much less power than PSR signals. SSR radar transmitters and antenna are, thus, smaller than their PSR equivalents, being, in general, narrower. (See Figure 20.1.)
Figure 20.1 A secondary surveillance radar head, on top of a PSR head.
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CHAPTER 20: SECONDARY SURVEILLANCE RADAR
SSR FREQUENCIES.
The ground station transmits and interrogates on 1030 MHz, and receives on 1090 MHz. The aircraft receives on 1030 MHz and transmits and transponds on 1090 MHz. The SSR ground antenna transmits in a narrow beam, while the aircraft transmits omni-directionally, in a circular pattern, around the aircraft.
THE BASIC LIGHT AIRCRAFT TRANSPONDER
The current types of basic transponder carried by general aviation aircraft mostly operate in two modes:
•Mode A. The basic transponder function which puts an identification code against the trace of an aircraft on the radar screen. The air traffic controller assigns the four-digit identification code (called a “squawk”) - a remnant of WW2 terminology when the IFF was codenamed ‘Parrot’), to a pilot, over the radio, and the pilot selects the code on his transponder.
•Mode C. Transponders with a Mode C function also transmit altitude information, based on the standard pressure setting of 1013.2 millibars
(hectopascals), from an encoding altimeter which must also be fitted to the aircraft.
(A requirement for aircraft to carry transponders with a Mode S capability is being introduced in Europe. Mode S transponders will emit a signal which is unique to a particular aircraft and which stays with that aircraft throughout its operational life. Mode S is covered in more detail later in this chapter.)
On the typical light-aircraft transponder of the type depicted in Figure 20.2, selecting ON activates Mode A. Selecting ALT activates Mode C alongside Mode A. If the aircraft is not fitted with an encoding altimeter, the transponder will function in Mode
A only. Figure 20.2 depicts the transponder selected to ALT; with the selector in this position, the transponder is operating in both Mode C and Mode A.
Figure 20.2 A transponder with ALT selected.
If SBY, signifying STANDBY, is selected on the transponder, the instrument is switched on but the transponder function itself is not activated. In the SBY mode, the transponder function will, however, be instantly available as soon as the pilot moves the selector to the ON or ALT positions.
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