Lecture 10

1. Lecture 10 Communication Radar & Radio procedures Chapter 5, Jeppesen Sanderson

2. Radar • What is Radar? • Primary Radar • How it works • Disadvantage • Secondary Radar • How it works • ATCRBS • Transponder Operation • On board radar

3. What is Radar? (1) • Radar stands for “radio detection and ranging”. • Primary radar is a ground-based system used by ATC to detect airplanes in the sky, or even those on the ground under limited visibility. • Primary radar detects a distant object (airplane), identifies its direction, and finds its range. The result is displayed on a 2-dimensional screen. • It uses a radio transmitter to send out radio waves that hit the object, then the radio receiver picks up the reflected waves from the object.

4. What is Radar? (2) • The emitter continuously sends out radio wave pulses, scanning different directions in sky. • The presence of a reflection in a certain direction indicates an object is present in that direction. • From the time lag between the emission and the detection of the reflection, the distance between the radar system and the object can be easily found, knowing the speed of the radio waves which is the speed of light (186,000 miles per second). (Fig 5-1)

5. Primary radar (5-1)

6. Disadvantages of Primary Radar • Primary radar system has some drawbacks: • Different regions of air can have different temperatures. This can cause the radar waves to bend, resulting in erroneous direction and/ or range readout. • When bent too low, ground objects like buildings produce “ground clutter” on the radar screen, • Clouds can block an aircraft from the radar waves. • No easy way to identify the aircraft detected. • No display of the altitude of the aircraft.

7. Secondary Radar • To overcome these drawbacks the Air Traffic Control (ATC) uses air traffic control radar beacon system (ATCRBS) – often referred to as secondary radar, together with the primary radar system. • Besides primary radar ATCRBS incorporates three additional features – an interrogator, a transponder, and a decoder. (Fig 5-2) • Interrogator – sends a coded question to plane • Transponder – on the plane sends coded reply • Decoder – on the ground decodes the reply

8. ATCRBS (5-2)

9. Transponder Operation (1) • A transponder, installed in the cockpit, has five operation states the pilot can choose from – ON, OFF, STANDBY, ALTITUDE, and TEST. • The controller (from control tower) assigns your aircraft a code, and tells you (the pilot) which operation mode you should be using. • The pilot uses a 4-digit code setter (in octal numbers, from 0 to 7) to set the code the transponder sends back to the controller when questioned.

10. Transponder Operation (2) • For example, 1200 (octal) is the code for VFR; 7500 is a code indicating the aircraft has been hijacked; 7600 indicate failure of two-way radio communication; and 7700 indicates an emergency. • Thus codes 7500, 7600 and 7700 should not be inadvertently set. (Fig 5-3) • When the controller talks to the pilot about transponder setting he voices out the word “Squawk”. (e.g., “Squawk Altitude”– activate the automatic altitude reporting mode of your transponder.)

11. The transponder (5-3)

12. More on Radar (1) • Fig 5-5 shows an example how different transponder features are used. • The FAA uses the radar system to check both aircrafts in flight as well as the airport. • Some military aircraft like the Lockheed F-117, or Stealth, are invisible to radar. • The surface of those aircrafts is coated with radar absorbent material to minimize reflection. • The surface is also constructed with small flat surfaces facing different directions to scatter any remaining reflection to different directions.

13. Example of using Transponder features (5-5)

14. More on Radar (2) – On Board Radar • To help avoid collision aircrafts usually carry on-board radar systems called Traffic Collision Avoidance System (TCAS). • TCAS sends out radar to detect if there is any other objects within a certain range of the plane. • If two planes are going towards each other, TCAS makes suggestions to climb for one plane and to descend for another plane to avoid collision.

15. ATIS • Around busy airports it would be difficult for controllers to give every aircraft a separate airport advisory. • Instead, the airport continuously broadcasts out updated airport information on its own frequency channel. This is called automatic terminal information service (ATIS). • In larger airports like HK International Airport there may be one ATIS system for departing aircraft and one for descending aircraft.

16. Radio Communication • VHF communication equipment • Using the radio • ATC facilities • Arrival and departure procedures • Emergency procedures

17. VHF Communication Equipment (1) • General aircraft communication radio uses a portion of the very high frequency (VHF) range, between 118 to 136 MHz. • Communication radios are classified by the number of channels they can accommodate – 360 channels or 720 channels. • A 360-channel radio divides the VHF range to 360 parts, .05 MHz each. For example, 118.05, 118.10, 118.15 can be channel frequencies.

18. VHF Communication Equipment (2) • A 720-channel radio divides the VHF range to 720 parts, .025 MHz each. Thus, 118.025, 118.050, 118.075, 118.10 can be channel frequencies. • Communication radios usually can receive as well as transmit signals. They are therefore called transceivers. • To receive ATC service services a 720-channel transceiver is required.

19. VHF Communication Equipment (3) • To use radio communication only objects in the line of sight is possible. Objects blocked by buildings, mountains cannot have radio communication between them. (Fig 5-15)

20. VHF Communication Equipment (5-15)

21. Using the Radio • It is recommended by ICAO that English be used for international communication. • Radio communications in aviation has to be • Accurate • Complete • Clear • Short • Because of these requirements special standard practices are used, including the use of phonetic alphabets.

22. Phonetic Alphabet • To improve clarity and minimize the chance of misinterpretation, single English alphabets are pronounced over the radio as a standard word. • The list of standard words for the 26 alphabets are called phonetic alphabets and are listed as in Fig 5-16. • Thus A is Alpha, B is Bravo, C is Charlie etc. • If a plane’s registration number is HK123, then to identify it over the radio, the pilot identifies it as Hotel Kilo 1, 2, 3.

23. Phonetic Alphabet (5-16)

24. Numbers over the Radio • Numbers are pronounced over the radio in the same way they are usually pronounced except the number 9, which is pronounced as niner. • For example, 294 is pronounced as two, niner, four. • The decimal point is pronounced as “point”. • Each plane has its registration number painted on the tail, and is usually a combination of five letters and numbers. They are sometimes referred to as tail number .

25. Numbers over the Radio (2) • On your initial callup to ATC or other facilities you should: • State the name of the facility you are calling • Give your aircraft type, model, or manufacturer, and registration number • For example, “Hong Kong Tower, Cessna Victor 2345 Romeo.” • To avoid any confusion on the time, the 24-clock system is used, eliminating the need to specify a.m. or p.m. • To avoid confusion of the local time from different locations, the coordinated universal time (UTC) is used. This is the time at 0° longitude (in Greenwich), and is therefore also referred to as Zulu time.

26. ATC Facilities (1) • The air space of the world is divided into individual Flight Information Regions (FIR). • The air traffic control (ATC) for each region is responsible by the air control center of a major airport in that region. • When you fly along an air route you are therefore informed, monitored, and controlled by the different ATC of the different regions along your route. • As you enter a FIR you establish communication with its ATC

27. ATC Facilities (2) • As you enter a FIR you establish communication with its ATC. As stated before, you give the name of the facility you are calling and your full aircraft identification. • If your message is short you can also include a request, as well as your position and altitude. • When you are finish with your message, if you use the word “over” it indicates that your transmission is complete and that you expects a response.

28. Arrival (1) • If you want to land on an airport after entering its FIR you should switch on its ATIS to listen to all the broadcast general information about the airport. ATC routinely provides you with wind, runway, and altimeter information. • Then you should contact “approach control”, the ATC function which provides separation and sequencing of inbound aircraft; also provides traffic advisories or safety alerts if necessary.

29. Arrival (2) • Approach control also provides a transponder code and asks you to ident. • The controller then acknowledges that your aircraft is in radar contact and gives you a clearance to proceed. • Later it will hand you to the controller of the ”control tower” . • You cannot land until you receive permission from the control tower. • During your roll-out, control tower will give you instruction for clearing the runway.

30. Arrival (3) • When you have to clear the runway the tower asks you to contact “ground control” on 121.9 MHz. • Ground control provides a taxi clearance for you to reach a parking area. (Fig 5-24) • Summary procedures for landing: • Listen to ATIS • Contact approach control • Contact control tower • Contact Ground control

31. Arrival procedures (5-24)

32. Departure (1) • If you want to takeoff and depart a controlled airport you likewise have to follow a rigid procedure and follow the guidance and instructions of different control facilities. • First of all, you again listen to ATIS for general airport information including altimeter setting and the active runway. • You should then contact clearance delivery informing the delivery your identity number and aircraft type. You should also specify that you have listened to ATIS. Finally, identify your destination or direction of flight. Clearance delivery may provide detailed departure instructions and then ask you to contact ground control.

33. Departure (2) • Ground control is an ATC function for directing the movement of aircrafts and other vehicles on the airport surface. • Before leaving the parking area you have to receive a clearance from ground control to taxi to the active runway. (Fig 5-22) • At the active runway you do a before-takeoff check-list of items in the plane. Then you switch to the control tower for takeoff clearance.

34. Clearance delivery and ground control (5-22)

35. Departure (3) • After takeoff, contact departure control and a controller will advise you if you are in radar contact already. • Radar contact would mean that your aircraft has been identified by the radar system and that subsequent flight following will be provided. • Being provided flight following means that the controller is observing the progress of your aircraft and provide instruction when necessary. (Fig 5-23)

36. Control tower and departure control (5-23)

37. Departure (5) • A summary of the departure procedure is as follows: • Listen to ATIS for overall airport information • Contact clearance delivery for detailed departure instructions • Contact ground control for permission to taxi • Taxi to active runway and do before-takeoff checklist • Contact control tower to get takeoff clearance • After takeoff contact departure control

38. Emergency Procedures (1) • An emergency can be either a distress or an urgency condition. • A distress is a condition of being threatened by serious and/or imminent danger and of requiring immediate assistance, such as fire, mechanical failure, or structural failure. • An urgency situation is when you become doubtful about your position, fuel endurance, weather, or any other conditions which might adversely affect flight safety.

39. Emergency Procedures (2) • A specific radio frequency (121.5 MHz) is used for transmitting emergency messages. • In distress situation, the pilot calls out the word MAYDAY. This silences any other users on this frequency. • The words PAN-PAN indicates an urgency situation. • Changing your transponder code to 7700 triggers an alarm at all radar facility control positions.

40. Emergency Procedures (3) • If you are lost, keep in mind the Five C’s –climb, communicate, confess, comply, and conserve. • Climb – climb for better radio and radar reception and coverage. • Communicate– communicate with any available facility • Confess– confess that you are lost when contacting ATC or any other ground facility • Comply– comply with assistance instructions • Conserve– consider reducing your power to conserve fuel. Ensure that the mixture is leaned properly to extend your endurance.

41. Emergency Procedures (4) • The emergency locator transmitters (ELTs) are emergency signaling devices for locating downed aircraft. • These are battery-operated transmitters that emit a distinctive audio tone on 121.5 MHz VHF and 243.0 UFH. • If subjected to crash-generated forces, ELTs will activate automatically. It will operate continuously for at least 48 hours.