Terms, Abbreviations and Q-Codes

Radiotelephony has a dictionary, and the exam quotes it. The definitions in this lesson come from ICAO Annex 10, Volume II and the PANS documents, and the questions test them almost word for word: which station is a land station, which transmission is addressed to nobody, which Q-code is magnetic and which is true. Read each definition as a lawyer would; the distractors are built from the one word changed.

Stations

Annex 10 sorts everything that transmits into named stations, and the service they belong to is part of the definition:

Aeronautical station — a land station in the aeronautical mobile service; in certain instances it may be located on board a ship or on a platform at sea, but it is defined as the ground end of the exchange.
Aircraft station — a mobile station in the aeronautical mobile service, other than a survival craft station, located on board an aircraft.
Aerodrome control radio station — a station providing radiocommunication between an aerodrome control tower and aircraft or mobile aeronautical stations.
Air-ground control radio station — an aeronautical telecommunication station having primary responsibility for handling communications pertaining to the operation and control of aircraft in a given area.
Network station and regular station — a network station is an aeronautical station forming part of a radiotelephony network; the regular station is the one selected from an en-route network to communicate with, or intercept communications from, aircraft in normal conditions.
Radio direction-finding station — a radiodetermination station using radio direction finding; the bearing service later in this lesson comes from it.

The umbrella over all of them is the aeronautical mobile service (AMS): a mobile service between aeronautical stations and aircraft stations, or between aircraft stations, in which survival craft stations may participate. The classic trap swaps the first two definitions, so hold the anchor: the aeronautical station is the land station, the aircraft station is the mobile one.

Methods of communication

The same chapter names the ways stations talk, and each name is precise about direction and audience:

Air-ground communication — two-way communication between aircraft and stations or locations on the surface of the earth; air-to-ground and ground-to-air name the two one-way halves.
Broadcast — a transmission of information relating to air navigation that is not addressed to a specific station or stations; ATIS and VOLMET, met later in this course, are broadcasts.
Blind transmission — a transmission from one station to another where two-way communication cannot be established, but where it is believed the called station is able to receive; this is what a pilot with a dead receiver keeps doing, and the communication-failure lesson builds on it.
Simplex — telecommunication between two stations in one direction at a time; single channel simplex uses the same frequency in each direction, which is ordinary RT, while double channel simplex uses two frequencies, one for each direction.
Duplex — telecommunication that can take place in both directions simultaneously, the way a telephone call works.
Radiotelephony network — a group of radiotelephony aeronautical stations which operate on and guard frequencies from the same family, and support each other in a defined manner to ensure dependable air-ground communication; the long-range HF organisation behind the en-route network stations above.
Readback — the receiving station repeats a received message, or an appropriate part of it, back to the transmitting station to obtain confirmation of correct reception.

Approach and holding vocabulary

Arrival has its own vocabulary, drawn from the PANS. These terms return with full procedures in other subjects; here the definitions themselves are the syllabus:

Clearance limit — the point to which an aircraft is granted an air traffic control clearance.
Expected approach time (EAT) — the time at which ATC expects that an arriving aircraft, following a delay, will leave the holding fix to complete its approach for a landing; the actual time of leaving depends on the approach clearance.
Holding procedure — a predetermined manoeuvre which keeps an aircraft within a specified airspace while awaiting further clearance.
Final approach — the part of an instrument approach procedure that begins at the specified final approach fix or point (or, where none is specified, at the end of the last procedure turn, base turn or racetrack inbound turn, or on intercepting the last track), and ends at a point near the aerodrome from which a landing can be made or a missed approach is initiated.
Procedure turn — a turn away from a designated track followed by a turn in the opposite direction, so the aircraft intercepts and proceeds along the reciprocal of that track; designated left or right according to the direction of the initial turn.
Base turn — a turn during initial approach between the end of the outbound track and the beginning of the intermediate or final approach track, where the tracks are not reciprocal; that one word separates it from the procedure turn.
Reversal procedure — a procedure enabling the aircraft to reverse direction during the initial approach segment; the sequence may include procedure turns or base turns.
Racetrack procedure — a procedure designed to let the aircraft reduce altitude during initial approach and/or establish itself inbound when entry into a reversal procedure is not practical.
Missed approach procedure — the procedure to be followed if the approach cannot be continued.

ATS abbreviations

The syllabus expects the everyday abbreviations to be read without hesitation. Grouped the way the learning objective groups them:

Flight conditions — VMC and IMC for visual and instrument meteorological conditions; VFR, IFR and SVFR (special VFR) for the rules flown under; CAVOK, spoken "cav-okay", for visibility, cloud and present weather better than prescribed values, defined in full in this course's weather-information lesson.
Airspace — FIR flight information region, UIR upper flight information region, CTA control area, TMA terminal control area, CTR control zone, ATZ aerodrome traffic zone.
Services — ATS air traffic services, ATC air traffic control, FIS flight information service, AFIS aerodrome flight information service, AIS aeronautical information services, ATIS automatic terminal information service, VOLMET meteorological information for aircraft in flight.
Time — UTC coordinated universal time, ETA and ETD estimated times of arrival and departure, ATA and ATD the actual times, EET estimated elapsed time, EOBT estimated off-block time.
Hours of service — H24 continuous day and night; HJ sunrise to sunset; HN sunset to sunrise; HO service available to meet operational requirements; HS service during hours of scheduled operations; HX no specific working hours.

Q-codes: the pressure pair

Q-codes are three-letter survivors of the telegraphy era, and two families remain in daily radiotelephony: pressure settings, and directions and bearings. The pressure pair should already be familiar from the air law course's altimetry lesson:

QNH — the altimeter subscale setting that makes the altimeter read aerodrome elevation on the ground; in flight it indicates altitude, the vertical distance above mean sea level.
QFE — the setting that makes the altimeter read zero on the aerodrome (or the runway threshold); in flight it indicates height above that datum.

Q-codes: the bearing family

Four bearing Q-codes describe one straight line between a station and an aircraft, read from either end and against either north:

QDM — the magnetic heading to steer, with no wind, to reach the station.
QDR — the magnetic bearing of the aircraft from the station: the radial it sits on.
QTE — the true bearing of the aircraft from the station.
QUJ — the true track to the station; rarely used in practice but alive in the exam.

Two conversions connect the four. Reading the line from the other end changes it by exactly 180 degrees, so QDM and QDR are reciprocals, as are QUJ and QTE. Switching norths applies the magnetic variation: with an easterly variation, true equals magnetic plus the variation. In the figure the aircraft sits on QDR 060 with variation 10°E, so the same line is QTE 070, and read from the aircraft's end it is QDM 240 and QUJ 250.

Asking for a bearing

The service that hands out these values is ground direction finding, whose measurement side the radio navigation course covers; here the syllabus wants the procedure on the air. The aircraft calls the aeronautical station, or the station controlling the DF network, on the listening frequency, states the service wanted by the appropriate phrase, and ends the transmission by repeating its call sign. If the transmission was too short for the station to take a bearing, the aircraft gives a longer one: two periods of approximately ten seconds, or whatever else the station requests.

The station's reply has a fixed shape, and the aircraft's obligation follows it:

The reply carries the appropriate phrase, the bearing or heading in degrees as three figures, the class of bearing, and the time of observation if necessary.
The aircraft repeats the message back for confirmation or correction as soon as it is received.
The station may refuse to give bearings when conditions are unsatisfactory or the bearing falls outside the station's calibrated limits, stating the reason at the time.

The class is the station's honesty declaration. Bearings are class A within ±2°, B within ±5°, C within ±10°, and class D worse than C. A single station can only give a direction; when DF stations work as a network their bearings are plotted together, and the control station can pass a position instead, in latitude and longitude or as bearing and distance from a named point, classed A within 5 NM, B within 20 NM, C within 50 NM and D worse than C.

Categories of messages

Annex 10 fixes the order in which the aeronautical mobile service handles traffic. Six categories, in descending priority:

Distress calls, distress messages and distress traffic — radiotelephony signal MAYDAY.
Urgency messages, including messages preceded by the medical transports signal — radiotelephony signal PAN PAN, or PAN PAN MEDICAL for medical transports.
Communications relating to direction finding — the bearing exchanges of the previous section.
Flight safety messages — movement and control messages, messages from an aircraft or its operator of immediate concern to an aircraft in flight, and meteorological advice of immediate concern to an aircraft in flight or about to depart.
Meteorological messages — met information to or from aircraft other than the immediate-concern advice above.
Flight regularity messages — the airline's operational traffic: serviceability of essential facilities, servicing of aircraft, schedule changes and their crew and passenger consequences, non-routine landings and urgently required parts.

Two refinements are worth holding. A NOTAM can fall anywhere from the third to the sixth category depending on its content and importance to the aircraft concerned. And the everyday clearance or position report a pilot exchanges with ATC is a flight safety message: fourth in the table, yet the highest category most flights ever transmit.