| � |
| � |
 |
IAMSAR Manual
|
 |
� |
| � |
|
Communications
2.1 Distress Communications
|
2.1.1 This chapter introduces distress alerting and SAR communications, and discusses mobile and land-based uses of communications equipment. The basic information on aeronautical and maritime communications, frequencies, equipment, and procedures provided here will need to be supplemented to gain adequate expertise. Specific information on how to use the systems and equipment must be obtained from communication service providers, equipment manufacturers, training institutions, and other available sources. Since the field of communications is vast, RCCs may find it useful to employ communications experts if they handle the majority of their communications needs directly.
2.1.2 Distress traffic includes all messages relating to immediate assistance required by persons, aircraft, or marine craft in distress, including medical assistance. Distress traffic may also include SAR communications and on-scene communications. Distress calls take absolute priority over all other transmissions; anyone receiving a distress call must immediately cease any transmissions which may interfere with the call and listen on the frequency used for the call.
2.1.3 Distress and safety communications require the highest possible integrity and protection from harmful interference. Any interference which puts at risk the operation of safety services or degrades, obstructs or interrupts any radio communications is harmful. Some frequencies are protected, in that they have no authorised uses other than for distress and safety. SAR personnel should be the last of all people to cause harmful interference, and should co-operate with law-enforcement authorities to report and stop incidents of interference.
2.1.4 Distress alerts may arrive at RCCs from a variety of equipment sources and via a variety of alerting posts. Alerting posts include, but are not limited to, coast radio stations (CRSs), Local User Terminals (LUTs) and Mission Control Centres (MCCs) of the Cospas-Sarsat System, Land Earth Stations (LESs) of the Inmarsat System, Air Traffic Services (ATS) units, public safety units such as police and fire departments, and vessels, aircraft, or other persons or facilities which may receive and relay such alerts. Alerting posts are any intermediary facilities which relay distress alerts between their source and the responsible RCC, and may even include other RCCs.
2.1.5 Aircraft or vessel's in distress may use any means available to attract attention, make their positions known, and obtain help. |
| � |
2.2 Aeronautical Mobile Service |
2.2.1 When an RCC is involved with an aeronautical emergency, close co-ordination will be needed between the RCC, the aircraft in distress, and various aeronautical services directly involved with aircraft operations. Some functions described below which are important to RCC duties may be performed by other than RCC personnel, by staff which perform both RCC and other duties, etc., depending upon the circumstances of the RCC and the aircraft in distress.
2.2.2 Frequency bands allocated by ITU for the aeronautical mobile service include some in the high frequency (HF) spectrum (3000 to 30000 kHz), the very high frequency (VHF) spectrum (30 to 300 MHz), and the ultra-high frequency (UHF) spectrum (300 to 3000 MHz).
2.2.3 Initial transmissions of aeronautical distress messages normally are on the frequency being used for en- route communications with the aeronautical stations. SAR facilities proceeding to assist aircraft should establish communications on that frequency. The frequency may be obtained from the controlling surface station; it will normally be used for initial communications and for ensuing communications among the distressed aircraft, assisting aircraft, and controlling surface radio station. Otherwise, when a SAR facility is within radio range of a distressed aircraft, the initial contact frequency would normally be 121.5 MHz for civil aircraft or 243 MHz for military aircraft of some States.
2.2.4 SAR procedures should be initiated if an aircraft or vessel becomes overdue or fails to make a report. For aircraft, this is usually accomplished through an ATS unit or the flight plan system. However, if radar or communications are unexpectedly lost with an instrument flight rules (IFR) or visual flight rules (VFR) aircraft, SAR procedures may be initiated.
2.2.5 Normally, a pilot should not be asked to change frequencies during an emergency without good reason. However, if the aircraft is in a remote location, air traffic facilities based at or near that location may be in a better position to assist. A decision to change a frequency should be based on the circumstances.
2.2.6 If necessary, and if weather and circumstances permit, RCCs may recommend that the aircraft maintains or increases altitude to improve communications, radar, or direction-finding (DF) reception.
2.2.7 ICAO Regional Air Navigation Plans (RANPs) or other regional SAR plans or agreements may provide guidance on selection of appropriate aeronautical frequency bands for SAR. (RANPs and other ICAO documents may be obtained from ICAO.) VHF Communications
2.2.8 The 121.5 MHz VHF AM aeronautical emergency frequency is normally only used for calling or for emergencies. In emergencies, the frequency may be used to provide:
- a clear channel between aircraft in distress and a ground station when normal channels are being used for other aircraft;
- a channel between aircraft and aerodromes not normally used by international air traffic;
- a common channel between aircraft, and between aircraft and surface facilities, involved in SAR operations;
- air-to-ground communications between aircraft and suitably equipped vessels and survival craft;
- air-to-ground communications with aircraft when airborne equipment failure prevents use of regular channels;
- a common channel between civil aircraft and intercepting aircraft or intercept control units, and between civil or intercepting aircraft and an ATS unit, if civil aircraft are intercepted; and
- a means for locating the signal source via land-based or mobile direction-finding.
2.2.9 Where a VHF frequency is needed for a common VHF channel between aircraft, and between aircraft and surface services involved in SAR operations, 123.1 MHz should be used when possible, and 121.5 MHz used if an additional frequency is needed. An ELT or EPIRB transmitting on 121.5 MHz may make the use of this frequency impractical for communications.
2.2.10 121.5 MHz services are normally available at any aeronautical facility where needed to ensure immediate reception of distress calls. Aerodromes should always monitor 121.5 MHz for voice emergency calls and ELT aural signals (which have a WOW WOW sound from the transmission of two alternating tones).
HF Communications
2.2.11 Frequencies 3023 kHz, 4125 kHz, and 5680 kHz may be used for on-scene and SAR co-ordination communications when range dictates need for high frequencies, when use of other frequencies or other factors make these the best frequencies available, or as a means for vessels and aircraft to communicate with each other. |
| � |
2.3 Maritime Radio Service |
2.3.1 Vessels communicate with coast radio stations and with each other on maritime frequencies available in MF, HF and VHF bands.
MF communications
2.3.2 Medium frequencies (MF -300 to 3000 kHz), seldom used by aircraft, are commonly used for maritime services.
2.3.3 Use of 500 kHz for Morse Code distress, safety, and calling transmissions has historically been popular, and has often helped to overcome language barriers. However, with the advent of more advanced technologies, use of 500 kHz is decreasing. As of February 1999, international requirements to have this capability aboard ships will cease. Silence periods on this frequency are observed for three minutes twice an hour, beginning at 15 and 45 minutes past each hour, to facilitate reception of distress calls, and in the last 15 seconds of each period to announce distress, urgency, or safety broadcasts.
2.3.4 The frequency 2182 kHz, an international maritime voice distress, safety, and calling frequency, is also available in designated SAR aircraft. Silence periods on this frequency are observed for three minutes twice an hour, beginning on the hour and at 30 minutes past each hour, to facilitate reception of distress calls.
2.3.5 MF Radio Alarms. A number of coast and ship stations are equipped to transmit the radio alarm signal on 500 kHz radiotelegraphy or 2182 kHz radiotelephony by means of an automatic signal-generating device. The signal actuates automatic devices giving an alarm to attract attention of operators not maintaining an aural watch, and is followed by the Morse signal "SOS SOS SOS" on 500 kHz radiotelegraphy and the spoken words "MAYDAY MAYDAY MAYDAY" on 2182 kHz.
(a) The radiotelegraphy distress alarm consists of a series of twelve dashes sent in one minute, the duration of each dash being four seconds, and the duration of the interval between consecutive dashes being one second.
(b) The radiotelephony alarm consists of two audio-frequency tones transmitted alternately (similar in sound to a two-tone siren used by some ambulances). It is sent continuously for a period lasting from 30 seconds to one minute. A long continuous tone at the end of the alarm signifies that the signal originated from a coast station and not a ship station.
(c) Radio alarms may only be used to announce: - that a distress call or message is about to follow; or - the transmission of an urgent meteorological warning; or - the loss of a person overboard, when help of other vessels is required and cannot be satisfactorily obtained by use of the urgency signal only.
(d) Tests of radio alarms are prohibited. HF Communications
2.3.6 A wide range of maritime HF frequencies are allocated, and subdivided for radiotelegraphy and radiotelephony. In certain areas of the world the radiotelephone frequencies 4125 kHz and 6215 kHz are designated to supplement the frequency 2182 kHz for distress and safety purposes.
VHF Communications
2.3.7 The frequency 156.8 MHz FM (Channel 16) is the international VHF maritime voice distress, safety, and calling frequency. The frequency 156.3 MHz (Channel 06) may be used on-scene.
|
| � |
| � |
|
|
� |
