What rules apply to RT transmitting technique?
- Messages should not consist of more than three items, comprising clearance, instruction or pertinent information.
- Complex messages containing many combinations of numbers, recommended to use no more than 2 items.
- Aircraft in emergency, student pilots or pilots with poor aviation English, this may be reduced to one item.
What is the normal format of an RT message?
- Callsign of addressee
- Callsign of originator
- Message
Eg. ‘Medway Control, Speedbird 401, request descent clearance’.
What information and instructions are transmitted by pronouncing each digit of the number individually, and what are the exceptions?
Aircraft callsigns, altimeter settings, flight levels, headings, wind direction and speed, pressure settings, airspeed, transponder codes, frequencies etc.
Exceptions:
- Numbers containing whole hundreds or thousands for altitudes, height or cloud height, and visibility and RVR.
- Flight levels that are whole hundreds.
Why do we need standard phraseology?
It is essential that ATC communication is precise and unambiguous. Many accidents have occurred due to poor RT discipline by controllers and pilots.
What is a radio wave?
Radio waves are part of the electromagnetic spectrum. They do not require a medium to travel through, and can travel at the speed of light over very long distances without being attenuated.
A wavelength is a measurement from crest to crest of the sine wave form. The frequency is the number of times the wave oscillates per second (cycles). The higher the frequency, the shorter the wavelength. One cycle per second= 1 Hertz.
What are the components of a radio transmitter and receiver?
Transmitter:
Microphone- converts sound waves to electrical signal.
Modulator- superimposes audio signal on carrier wave (clean sine wave)
Radio Frequency Oscillator- generates radio-frequency carrier wave.
Transmitting Antenna- transmits radio wave.
Receiver:
Receiving Antenna-
Tuner- picks up transmitted radio frequency signal
Demodulator- moves carrier wave
Amplifier- boosts audio signal to high enough level to drive speaker
Speaker- converts audio signal to sound waves
What frequency bands are used for different ATC areas?
HF for Oceanic flights
VHF for RTF between ATC and aircraft
UHF for RTF on the ground between ATC and vehicles (better signal but less range).
How can radio waves be affected by the medium they are travelling though?
Reflected, refracted, attenuated, absorbed and diffracted (divided).
What are the two ways that radio waves travel from transmitter to receiver?
Ground waves:
Travel directly, following a straight, line of sight path. Signals received will be almost entirely ground waves. Repeater stations may be used to increase range.
Sky waves:
Signals travel upwards into the sky from transmitter- HF band and below are absorbed and refracted by the Ionosphere (UV radiation from sun ionises some gas molecules in upper atmosphere, thickest during day), VHF and higher travel into space.
What are the limitations of HF and NDB signals?
Static Interference- precipitation and thunderstorms.
Station Interference- frequency congestion, care needed with selection and identification (cure- protected range)
Night effect- ground and sky waves interact and cause fading (phase cancellation?)
What is antenna shadowing?
When an aircraft turns, the VHF antenna may be shadowed by other parts of the airframe. Less so with modern aircraft as they have both top and bottom antennas.
What is Selcal?
Selective Call- a means of identifying aircraft automatically when operating on HF.
Used by companies/ATC to send messages over long distances (often oceanic). Pilots don’t have to listen out on very noisy frequencies (caused by static and frequency distortion).
Works by sending two, two-tone signals, chosen from a list of frequencies in the audio range. This operates a chime in the relevant cockpit.
What is the Aeronautical Fixed Telecommunication Network (AFTN)?
A worldwide system of aeronautical fixed circuits, for the exchange of messages and/or digital data between aeronautical fixed stations, having the same or compatible communications characteristics.
What are the conditions for the acceptance of an AFTN?
1) Must be in 1 of 8 eligible categories:
Transmission Priority 1:
- Distress (SS): threatened by grave and imminent danger
Transmission Priority 2:
- Urgency (DD): concerning safety of a ship, aircraft or other vehicle, or of a person on board or within sight
- Flight Safety (FF): a) movement and control messages (flight plans and updates), b) messages originated by an aircraft operating agency of immediate concern to an aircraft in flight or preparing to depart, c) urgent meteorological information (SIGMETS)
Transmission Priority 3:
- Meteorological (GG): messages concerning TAFs and METARs.
- Flight Regularity (GG): eg aircraft load messages, changes in operating schedules
- Aeronautical Information (GG): NOTAM, SNOWTAM
- Aeronautical Administration (KK): operation or maintenance of facilities, functioning of tel services, messages exchanged between CAAs relating to aeronautical services.
- Service: Messages to obtain info or verification concerning other messages which appear to have been transferred incorrectly.
2) Must be addressed to a station forming part of the AFTN.
3) Text must not exceed 1800 characters in length.
What is the format of an AFTN message?
- Priority Indicator
- Addressee(s) (4 letter location indicator, 3 letter company designator, 1 filler letter, eg. EGLLZPZX- Heathrow ATS reporting office)
- Date/Time group (day of month, time in UTC)
- Originator (same as addressees)
- Text to be communicated
What is the Readability Scale for RT?
Method of measuring how clear RT transmissions are.
1 Unreadable 2 Readable now and then 3 Readable but with difficulty 4 Readable 5 Perfectly Readable
What is the issue of Callsign Confusion?
Similar callsigns on the same frequency can cause confusion which may lead to an incident.
Pilots of aircraft with callsigns which have in common three or more digits, especially with the same flight numbers, or aircraft with similar registrations should be warned by controllers and, if necessary, one of the flights should be instructed to use a different Callsign.
What messages are pilots to read back in full? (12 points)
- Taxi instructions
- Level, heading and speed instructions
- Airways or route clearances
- Approach clearances
- Runway-in-use
- SSR operating instructions
- Altimeter settings
- Clearance to enter, land, take off, backtrack, cross or hold short of any active runway
- VDF information
- Frequency changes (which should never be preceded by another transmission which requires read back)
- Type of air traffic service
- Transition levels
NB The pilot must be prompted if there is no read back, and corrected until it is accurate.
What rules apply to Landline Telephone communications? What significant information requires read back?
- Must announce station identity on all phone calls including direct lines. This is because mistaken identity can occur if a line is inadvertently left open from a previous call.
- Identity to be used is the function relative to the telephone extension being used (approach controller for approach, planner for planning etc.)
Read back of:
- Levels
- Headings
- Speed restrictions
- Airways/route instructions
- Runway-in-use
- SSR codes
- Pressure settings
- Frequencies
- Release and contact points
What rules govern the transfer of company messages to the aircraft by RT?
When requested, controllers MAY transmit operational messages, as long as safety is not compromised during the transmission and it is not during a critical phase of flight.
Transmission prefaced with “Company advise/request…”
Any messages affecting the safety of the aircraft in flight should be passed immediately using the precise wording given to the controller.
