(ii) Homing. The procedure involved in flying to a radio station guided by the use of the aircraft direction-finder without regard to position fixes obtained from off-line stations.

(jj) Initial Air Traffic Control Center. The air traffic control center in control of the area which includes the point of departure of a flight.

(kk) Initial Meteorological Office. The meteorological office [responsible] for issuing meteorological information to an aircraft prior to its departure on a flight.

(11) Intermediate Landing Area. A landing area along a route at which a stop is planned as specified in the flight plan.

(mm) International Communication Service. A telecommunication service between offices or stations belonging to different countries or between stations of the mobile service, unless these latter are of the same nationality and are situated within the limits of the country to which they belong.

(nn) International Radio Silence. Three-minute periods of radio silence, on the frequency of 500 kilocycles only, commencing at H+15 and H+45, during which all radio stations may listen on that frequency for distress signals of ships, aircraft, and other transportation units.

(oo) Land Station. A station not capable of being moved, carrying on a mobile service.

(pp) Mobile Service. A radio service carried on between mobile and land stations and by mobile stations communicating among themselves, excluding special services as defined in General Radio Regulations (Cairo Revision).

(qq) Mobile Station. A station capable of being moved and which ordinarily does move.

(rr) Non-Scheduled Flight. A flight over a specified air route, which is not one of the routine scheduled operations of an operating agency.

(ss) Operating Agency. A civil or military air transport operator or company.

(tt) Point of No Return. A point on a flight path marking one half the extreme range of an aircraft from the last point of departure, calculated on continuous use of all engines and adjusted for fuel load, reserve excepted, and forecast wind direction and velocity, outbound and return.

(uu) Position Report. A message, in a specified form, containing relevant items of information on the position and progress of an aircraft.

(vv) Pre-Flight. Used in connection with action to be taken before take-off of an aircraft.

(ww) Radiobeacon Station. A special station, the emissions of which are intended to enable an on-board station to determine its bearing or a direction with reference to the radiobeacon station, and in some cases also the distance which separates it from the latter.

(xx) Radio Bearing. The measurement of the angle formed by the direction of North to the direction of the waves sent out by a transmitting station, on their arrival at the receiving station taking the measurement. "True" bearings and courses are given in relation to true North. "Magnetic" bearings and courses are given in relation to the magnetic North.

(yy) Radio Direction-Finding Station (D/F). A station equipped with special apparatus for determining the direction of the emissions of other stations.

(zz) Radio Range. A form of radiobeacon, the emissions of which are controlled to provide definite track guidance to mobile stations. (aaa) Radio Silence. A period during which all scheduled and other radio transmission is foregone by a radio station.

(bbb) Regional Headquarters. For the purposes of this Annex, Regional Headquarters means the headquarters office of each region in the international organization for air navigation.

(ccc) Request-Information Message. A message, in a specified form, addressed by one air traffic control center to another to obtain information of the current position or location of an aircraft.

(ddd) Rescue Facilities. Rescue and search services, relief aircraft, and other measures for physical aid to aircraft in distress.

(eee) Route-Section. The portion of an airway between an airport, or intermediate airport, and a control area boundary.

(fff) Route-Stage. The portion of an airway between an intermediate airport and a departure airport or destination airport, or between two intermediate airports.

(ggg) Scheduled Flight. A flight listed in schedules of operation promulgated in advance by an operating agency.

(hhh) Special Flight. A flight which is operated over a course which is not a recognized airway.

(iii) Telecommunications. Any telegraph or telephone communication of signs, signals, writings, images, and sounds of any nature, by wire, radio, or other systems or processes of electric or visual (semaphore) signalling.

(jjj) Warning Message. A message, in a specified form, containing relevant items of information on the proposed flight of an aircraft.

SECTION II

Organization

1. Licenses for Aircraft Stations. Requirements are outlined in General Radio Regulations (Cairo Revision).

2. Aircraft Radio Operators' Licenses. Requirements are outlined in General Radio Regulations (Cairo Revision).

3. Categories of Service. The primary object of the communications service is to insure the safety of air navigation and the regularity of air traffic. Where these services are required they will be designated as indicated below:

Synoptic meteorological reports
Forecasts

"D"

"E"

"F"

"G"

Other meteorological chart data and advice

Broadcasting of meteorological information to aircraft via radiotelephone and radiotelegraph

Radiocommunication to and from aircraft

Aircraft control communications point-to-point
Monitoring of facilities

Service Identification "H"

"I"

"K"

"L"

"M"

"O"

"R"

"T"

"W"

"X"

Operational Services

Radio beacon (aerophare, radiophare) transmission from ground
stations (Class "H" facilities)

Various intermediate landing area communications services not
covered specifically elsewhere, e. g. visual or sound signals
Special information service between aircraft communicators and air-
men relative facilities, aids, and matters requiring close liaison
between airmen in flight and airmen on the ground (Flight Com-
munications Service)

Airway light facilities between landing areas and at landing areas
Radio markers, particularly on radio range courses

Dissemination of meteorological information from foreign and overseas
points

Radio range operation

Commercial telephone and other commercial communications systems
Meteorological observation by aircraft communicators

Direction finding

NOTE: Messages shall be handled on any of the communications circuits where time is available.

(a) The messages necessary to insure the safety of air navigation and the regularity of air traffic are defined in Section III. 4. Communications in the Aeronautical Service

(a) General. Every aircraft compulsorily provided with radio communication apparatus, shall, when such apparatus is equipped to work on the frequencies of the international service, keep a continuous watch on the calling frequency or frequencies in force in the area flown over, unless it is exempted therefrom by the communications control station with which it is in communication.

(1) As a general rule, it shall rest with the aircraft station to establish communication with the aeronautical station. Each aeronautical ground station shall maintain a continuous guard on the aircraft frequencies as necessary in connection with each flight.

(2) In principle, an aeronautical station having radio traffic for an aircraft station which has not made its presence known, shall not call this station unless it has reason to believe that such aircraft station is within range and is maintaining watch on the required frequencies.

(3) In communications between aeronautical stations and aircraft stations, the aircraft station shall conform to the instructions given by the aeronautical station in all questions relating to the order and time of transmission, to the choice either of the frequency or the type of emission or, both the frequency and the type of emission, and to the suspension of work. This provision shall not apply to cases of distress.

a. In communications between aircraft stations, except in cases of distress, the station called shall control the working as indicated above.

b. In communications between aircraft stations, the duration of periods of working shall be fixed by the receiving aircraft station, subject to the right of the aeronautical station to intervene for that purpose. In communications between aeronautical stations and the aircraft stations, the aeronautical station shall fix the duration of periods of working.

c. A continuous watch shall be maintained on the aircraft station throughout the flight. The aircraft station shall normally

maintain communication only with the communications control station, and shall not change frequency without first obtaining the concurrence of that station, except when another of the specified or agreed frequencies must be used to maintain communications.

d. Communications schedules for each flight shall be determined by agreement between the operating agency and the appropriate communications control station. QRU's shall be exchanged at scheduled times, except when messages are being sent, and shall be transmitted to the operating agency. Messages to and from the aircraft may be transmitted at any time without waiting for a scheduled period.

e. Bearings (D/F). Bearings shall be given to aircraft on request only.

f. International silence periods. No transmissions, except those relating to distress or emergency, shall be made on 500 kilocycles during the international silence periods.

g. Aircraft radio silence. In cases where it is necessary to observe radio silence, an aircraft, if possible, shall inform the communications control station beforehand by sending, on the air-ground frequency in use at the time, the signal "QRX”, followed by the time (Greenwich) at which it is expected communication will be resumed. (Example: QRX 0230.) When transmission is again possible, the aircraft shall call the communications control station on the same frequency and send the appropriate "Q" signal.

h. If silence must be continued beyond the time specified in the "QRX" notice, a "QRX" with revised time of resumption of communication shall be transmitted by the aircraft station at or near the time first specified, if at all possible.

(4) Except in the case of distress, communications between aircraft stations shall not interfere with the working of aeronautical stations. When such interference occurs, the aircraft stations which are the cause of the interference shall stop transmitting or change their frequency at the first request of the aeronautical station. concerned.

(5) Continuous transmission by two or more stations in communication with each other handling mobile traffic shall not exceed 10 minutes.

a. After each of these periods a pause shall be observed in order to permit, if necessary, another station to send a priority call or to transmit a priority message.

(6) When an aeronautical station is called at the same time by several aircraft stations, it shall decide the order in which the aircraft may communicate with it.

(7) In case certain aircraft are flying in instrument conditions, the land stations liable to enter into communication with them shall notify other aircraft that they must reduce their communications to a strict minimum, by transmitting for this purpose the appropriate "Q" signal.

(8) Under Abnormal Circumstances. In abnormal circumstances, an aircraft station shall consider use of any relay to transmit messages to the communications control station. A communications control station shall consider use of any relay in order to clear messaegs to an aircraft. The aircraft station shall, if possible, continue to transmit the QRU signals to the communications control station at the scheduled times and on the normal frequencies, when using relay.

a. In the event of a break-down in communications, the communications control station shall broadcast any messages for the aircraft at the assigned scheduled time. Should the breakdown be assumed to be due to the failure of the transmitter at the communications control station, the aircraft station shall continue to use the transmitting frequency then in use and listen for the communications control station on the point-to-point frequency in operation at the time. The aircraft station shall be kept informed by the communications control station of changes in the frequency used for point-to-point working.

5. Normal Operation of Ground Stations. Continuous watch shall be maintained or scheduled contacts shall be made between aeronautical ground stations as necessary in connection with each flight.

6. Abnormal Operation of Ground Stations. Should communication on a normal point-to-point channel fail, the aeronautical ground stations concerned, while continuing efforts to establish contact on an appropriate alternate frequency, shall also endeavor to establish contact on the air-ground frequency in use at the time. The communications control stations shall keep the other aeronautical ground stations concerned advised of changes in the air-ground frequency.

(a) Relay and Cable. In the event of a break-down of radio-communication between any two aeronautical ground stations, or in case of abnormal delays in point-to-point communications, efforts shall be made to relay traffic via any radio station with which communication is possible. If this fails, use shall be made of cable or other available facilities.

(b) Should efforts to establish contact with another aeronautical ground station be unsuccessful, a listening watch shall be maintained on the point-to-point frequency normally in use at the time, and traffic shall be "broadcast" on that frequency. The station's call sign and V's shall be transmitted for a period of not longer than 3 minutes before the traffic is transmitted.

7. Notices to Airmen. Steps shall be taken to issue where possible any information affecting the safety of air navigation over their territory by Notices to Airmen and to insure appropriate circulation. of these documents, through the medium of a central international air navigation bureau, if established.

(a) The contents of such Notices to Airmen will be disseminated either:

(1) By communications stations in accordance with published practice, only if their urgency is sufficient to warrant such transmission.