made and believed to be generally applicable that the SEARCH AIRCRAFT begins its search from a base so located as to provide a distinct speed advantage over the SEARCH SHIP adjudged to be nearest to the location of the survivors.

The availability of SAR aircraft throughout the world is shown in the Air Navigation Plans published by the International Civil Aviation Organization (ICAO). These indicate the existence of extended coverage.

It seems clear that the foregoing analysis supports the choice of SAR AIRCRAFT as the more effective search and interim-aid mobile unit. Although it is realized that this will not hold true in all cases, it is firmly believed that where a choice must be made (for logical selection of the best single beacon frequency) on a worldwide basis, the weight of all relevant factors is distinctly in favor of the search aircraft as the greatest potential aid to the largest number of survivors.

Considering now the third point made by the IMCO Maritime Safety Committee that, except under conditions of difficult propagation, the signals from the position-indicating beacon must be receivable at the distance over the sea of at least 30 nautical miles, the Radio Technical Commission for Marine Services does not, on the concept of surface to aircraft transmission, agree with the Maritime Safety Committee. RTCM concurs with the present position of the U.S. Coast Guard that the beacon signals should be receivable up to 100 nautical miles by an aircraft fitted with a modern radio-beacon receiver in efficient working condition and in flight at an altitude of not less than 10,000 feet above sea level. (Reference-RTCM Distress Systems Study Group document C-1-DS-56, p. E.)

Points (5) and (6) of the IMCO Maritime Safety Committee position are not within the scope of this report. The remaining part of this paper deals with the 4th point of the IMCO position, i.e., the selection of a first-choice operational frequency for emergency position-indicating beacons.

Operational Requirements for Emergency Position-Indicating Bea

cons

Because the optimum single frequency to be selected for emergency position-indicating beacons is fundamentally related to its operational requirements, these requirements must be taken into account before consideration can be given to comparing the relative merits of the available frequencies. For this purpose, only broad general requirements pertinent to the

IMCO ON EPIRB

Recommendation 48, of the 1960 Conference on Safety of Life at Sea, recommends equipping all vessels where appropriate with floatable, selfenergizing radio beacon, the radio characteristics of which should conform to a standard of worldwide application. These characteristics should be determined after consultations with ICAO and ITU. In the course of these consultations, the radio characteristics of such an equipment and the requirements for its worldwide application were the subjects of discussions within the Organization and the views of Member Governments were sought. In the light of the information collected, the problem was considered by the Maritime Safety Committee which formulated the following views:

(1) The beacons are intended primarily for homing;

(2) stations expected to receive the transmissions from the beacons are primarily ships and SAR aircraft;

(3) except in areas with difficult propagation characteristics, the signals from the beacons must be receivable at a distance of at least 30 nautical miles at sea level;

(4) the frequency of 2182 kc/s is recommended as a first choice operational frequency for the radio beacons. It should, however, rest with Administrations to determine whether the equipment should allow for the use of a second or more frequencies and, if so, to decide on the choice of those frequencies;

(5) the beacons should transmit intermittently;

(6) if it is possible, within the specifications stated above, the beacon may also be used for alerting in appropriate circumstances. In that event, the beacon should incorporate a characteristic identifying signal. The CCIR should investigate whether this signal could serve also as an alerting signal or whether the two-tone signal should be introduced for those cases where no alerting had been possible by other means.

The International Radio Consultative Committee (CCIR) of the ITU has been asked to prepare detailed specifications for the radio beacons, on the basis of the requirements of IMCO and ICAO.

Following the Committee's Recommendation, the subject was discussed by other technical bodies outside IMCO. Two points attracted special attention:

(a) Type of "intermittent" transmission

The term "intermittent" indicates the need for periods of silence alternating with periods of operation of the beacon.

One view favors short periods "on" and relatively longer periods "off" in order to avoid confusion and cluttering effects, particularly in cases and areas where more than one beacon may operate at the same time. On the other hand it is pointed out that searching aircraft, when passing overhead, may miss the beacon if the passage happens during the "off" period. It seems that the "on-off" ratio should be such as to permit taking bearings for homing purposes.

(b) Type of “identifying” signal

In view of the fact that the beacon is intended primarily for homing, it is assumed that the alerting phase has already been completed. Therefore, the identifying signal need not be the two-tone alarm. However, there may be cases where no alerting has been possible by other means. It should therefore be investigated whether the identifying signal (if it is not the two-tone alarm) could also serve as an alerting signal or whether the two-tone alarm should be introduced in the beacon.

It is understood that tests have been carried out recently by the French and German Authorities.

immediate problem will be regarded as the limiting factors. RTCM studies made of this subject indicate that a practical position-indicating beacon for emergency use at sea must meet the following conditions, among others:

(1) Under distress conditions, its operation must be completely automatic.

(2) It must float free from any other unit, and must operate even though a heavy sea is encountered with rain, snow, or sleet.

(3) The antenna (radiator) must be a low vertical rod or mast (nominally about 6 to 8 feet or less) with high radiation efficiency even under conditions of heavy spray and high waves.

(4) The average power consumed by the beacon must be as low as practicable, nominally from 1 to 3 watts input to the transmitter.

(5) The beacon transmitter must have good radio-frequency stability. Consequently, the frequency on which the beacon is to transmit should, in so far as may be possible, be a frequency which will best enable the beacon to comply with the above-listed basic operational requirements. Comparison of Frequencies

The frequency to be selected must be available under International Radio Regulations for use worldwide without restriction and as free from interference by other stations as is possible. Prior to any consideration of the merits of different characteristic frequencies, therefore, there must first be set forth the relatively few frequencies which may be legally used under the governing treaty. These are 500 kc/s, 2182 kc/s, 8364 kc/s, 121.5 Mc/s, and 243 Mc/s. At the outset, it should be understood that the existence of a watch or automatic monitoring system on any of these frequencies has no bearing on the question of determining the optimum frequency. This is so because, as has already been stipulated, the primary purpose of the beacon is for homing after word of a distress situation has arrived possibly via other radio frequencies, even though two of these frequencies, namely 500 kc/s and 2182 kc/s, are international distress frequencies. Thus, listening on the beacon frequency by searching craft subsequent to a distress incident will each time be initiated by the normal processes of the established search and rescue facilities. The problem, therefore, is one of deciding which of these five frequencies will provide the most effective transmission under the limitations herein set forth concerning the operational requirements, using equip

ment not based upon the number of units of a particular kind predominantly in present use, but instead, equipment which will provide the best performance on the condition, of course, that it is technically and economically feasible.

Relevant technical characteristics of the five available frequencies are set forth herewith from the viewpoint of transmission to high-flying SAR aircraft.

500 kc/s and 2182 kc/s

These two frequencies have several characteristics in common. Their effective use under limitations of low power and small-size containers for equipment is very doubtful. The very small antenna possible on the beacon would result in very low radiation efficiency, and the relatively high voltage developed at the low point of the antenna would cause electrical leakage of power from the effect of salt water moisture. Unattended transmission on these frequencies for extended periods of time could cause interference to distress and emergency signals of other stations in certain locations near ships and coast stations. Concerning reception, both frequencies would be subject to interference from other stations and to atmospheric interference, the latter mostly during the summer months and at the lower latitudes. Receiving antennas aboard aircraft present a more troublesome antenna situation for 500 kc/s than for any other available beacon frequency. U.S. Coast Guard aircraft can utilize either 500 kc/s or 2182 kc/s effectively for both direction finding and homing. On small boats, direction finding and homing can be conducted effectively on either 500 kc/s or 2182 kc/s. However, as the size of a vessel increases, with corresponding complexity of superstructure and antenna arrays, direction finding on 2182 kc/s becomes erratic. This is due to irregular cross-over points or locking of the direction finder on a particular bearing. Because of this fact, it has become standard practice in the U.S. Coast Guard to use 2182 kc/s for homing only, restricting calibration to an arc within 30° on each bow.

8364 kc/s

Low power and small physical transmitter space would not be a problem in the case of 8364 kc/s. The small beacon antenna, while not favorable to a frequency of this order, would provide an acceptable degree of radiation efficiency. Unattended transmission on this frequency is not likely to cause interference to a distress signal, although it could do so

on rare occasions when this frequency might happen to be carrying such signals at the same time. In regard to reception, atmospheric noise level would be low, and interference from other stations would occasionally give trouble. It has been demonstrated in practice that an efficient network of land-based direction finding receiving stations can determine within rather narrow limits the location of a beacon operating on a frequency of this order, even though transmission is over long distances. Sky wave reception of this frequency is not regarded as useful for accurate homing by search aircraft. Within less than about 15 miles from the beacon, the signals would probably be satisfactory for homing.

121.5 Mc/s and 243 Mc/s-VHF

These frequencies generally have common technical characteristics. The use of low power, small physical space, and small antennas are no problems of significance. The sizes of beacon transmitter antennas, in fact, are about optimum for these frequencies, and high radiation efficiency results. Transmission ranges to highflying aircraft are limited to the ranges actually useful for effective searching operations. The element of long-distance interference from other stations is, except for very rare occasions of unusual propagation conditions, entirely absent. Further, there is practically no atmospheric interference present at any time. The leakage effect of salt water spray on the antenna is minimized by antenna circuitry that places the lower part of the antenna practically at ground electrical potential. Also, it is within the realm of practicability to employ specially engineered antennas that will provide a significant gain in radiation equivalent to an actual increase in power. Although experience to date indicates that the surface-tosurface transmission range of these frequencies is limited to a very few miles, improvements of this range from possible future technical developments cannot be ruled out. Unattended transmissions on these frequencies could create interference to civil or military aircraft stations while they are within the limited range of the beacon, but this does not appear to be a significant disadvantage; the possibility is rather infrequent, and the interference area is comparatively small. It is assumed, of course, that such beacons would be used solely in actual cases of distress.

At these frequencies, and more especially at 243 Mc/s, frequency instability can cause unreliable opera(Continued on page 289.)

IN ITS RECOMMENDATION No. 48, the International Convention on Safety of Life at Sea (London, 1960) recommends that governments should encourage the equipping of all ships where appropriate with emergency radio beacons in order to facilitate search and rescue actions at sea. Since 1960 the question has been under study by IMCO, ICAO and ITU, but it has proved extremely difficult to solve this problem in a satisfactory way on a worldwide basis with equipment which would use a single frequency.

In Norway, urgent need has been felt on several occasions for an emergency position-indicating radio beacon. We have reason to believe that equipment of this nature could have saved human lives in a number of distress situations which have occurred along our far-stretching coast.

In planning the design of an emergency radio beacon as recommended in the Convention on Safety of Life at Sea, we especially considered the following points:

1. Frequency.

2. Class of emission.

3. Range.

4. Way of starting the operation of the beacon.

Frequency.

The rescue vessels of Norsk Selskab til Skibbrudnes Redning (NSSR) (The Norwegian Life-Boat Association) are all equipped with direction finding equipment covering the frequency range 285-535 kc/s as well as a part of the 2 Mc/s band, including the distress frequency 2182 kc/s. There are also at all times in Norwegian waters a number of fishing vessels and coasters fitted with MF radiotelephone installations and to a great extent also with D/F equipment capable of operating on the frequency 2182 kc/s.

In distress traffic, silence may be imposed on the frequency 2182 kc/s, a factor of great importance which may facilitate homing on signals from a low power emergency radio beacon. Another factor is that continuous watch is being kept on 2182 kc/s by the NSSR rescue vessels and by the

coast stations. If a receiver with beat-oscillator is used, signals on 2182 kc/s from a low power emergency radio beacon may be picked up without difficulty. On the basis of these considerations, Norway has chosen the frequency 2182 kc/s for an emergency radio beacon for national use. Class of emission

When considering the choice between keying without the use of a modulating audio frequency (class of emission A1) or keying with the use of a modulating audio frequency (class of emission A2), we took into account the fact that the radio beacon should not necessarily in itself have an alerting capability, nor should the signals transmitted by the beacon cause interference to distress traffic on the frequency 2182 kc/s. Using a low power A1-transmitter, we have carried out practical tests specifically in this connection without observing to any appreciable extent interference to communications on the said frequency.

We have further assumed that normally a distress signal will be transmitted from the ordinary radiotelephone installation of the mobile station in distress. It may however not always be so, but in any case, when a vessel has been reported as missing, it will be possible to listen for signals with the class of emission used by the emergency position-indicating radio beacon. On the basis of these considerations use of A1 class of emission was deemed appropriate.

Range

As to the range of an emergency radio beacon using the frequency 2182 kc/s, there are a number of problems to be considered, e.g., the quality of bearings taken by vessels equipped with conventional loops, field strength ratio of the direct to the indirect wave on the reception site and the signals from the beacon in relation to distress traffic as mentioned under 2 above. We have come to the conclusion that a range of about 50 nautical miles under day conditions might be acceptable for search actions, taking

sar seminar

into consideration the transmission conditions on the frequency in question. Our practical tests have shown that a radio beacon with a range of 50 nautical miles under day conditions will have a range of 30-35 nautical miles under night conditions.

Starting the beacon

It has been discussed whether the beacon should start automatically after having been thrown into the sea. In Norway we are of the opinion that this solution is not desirable as beacons may get into the sea accidentally and thereby perhaps set off a costly search action to no purpose. We are therefore at present of the opinion that the beacon should be capable of being mounted by simple means on board craft, lifeboats, rafts, etc. and started by human action.

Norwegian authorities have already, for national use, in conformity with Item 2 of IMCO Doc. IGR 1/2 of 2 June 1962, approved a type of emergency position-indicating radio beacon designed to meet the requirements outlined above.

The frequency used in 2182 kc/s, class of emission A1. It is fully transistorized, self-energizing and capable of 4 to 5 days' continuous operation. The beacon transmits dashes of a duration of 7, 10 or 12 seconds.

The transmitter with necessary accessories, aerial, earth connection and fastening device, is packed as one unit in a plastic case with great buoyancy. The outside measurements are 60 x 21 x 15 cm. and the weight is a total of 10 lbs.

It can, if necessary, be thrown into the sea, then picked up, mounted and started by the survivors. The equipment in question may be modified to a radio beacon which starts operation automatically when thrown into the sea. The class of emission may be changed to A2.

As already stated, we doubt the advantages of such modifications, but we would appreciate very much comments by other nations having experience based on practical tests with emergency position-indicating radio beacons.

(Continued from page 286.)

tion unless good engineering and maintenance measures are effectively applied. This is particularly applicable to receiving equipment in which the frequency of oscillators may not be measured as often as for transmitters. However, this is mentioned as a precautionary note rather than as an unavoidable disadvantage.

Because of their harmonic relation, both of these frequencies may be used either simultaneously or alternately for a single beacon without significant technical complications and thus without a substantial increase in cost. Conclusion

Considering all factors herein previously reviewed which pertain to a logical choice of one of the five frequencies available for emergency position-indicating beacons, the balance is considered to be definitely in favor of either 121.5 Mc/s or 243 Mc/s. In consequence, the following recommendation is made.

Recommendation

Emergency Position-Indicating Beacons should radiate on 121.5 Mc/s but, when desirable because of the area of operation of the vessel, should also radiate a signal on 243 Mc/s for compatibility with long-range military aircraft equipment. If, however, these frequencies were interchanged in regard to order of preference designated in this Recommendation, the search function would not be affected significantly.

IMCO

(Continued from page 271.)

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be encountered when carrying cargo in bulk.

The need for international rules covering the carriage of dangerous goods in ships has been in existence for a considerable time. A recommendation to this effect was made as far back as the 1929 SOLAS Conference. The SOLAS 60 Conference strengthened this need. Acting upon Recommendation 56 of the latter Conference, IMCO undertook a study of the subject. The results of this study were approved by the 4th Assembly. Six of the nine classes have been completed and with the approval of the final three classes by the Maritime Safety Committee the Code will be submitted to member states for adoption as a basis for national regulations.

NEW STUDIES

In approving the work program recommended by the Maritime Safety Committee the Assembly approved the establishing of three new subcommittees on (1) Special Types of Craft, (2) Life Jackets and (3) Efficiency of Navigation Matters.

Lights and Related

The Subcommittee on Special Types of Craft was established to study the operational requirements concerning the safety of navigation of vessels such as hydrofoils and hovercraft. This study will also cover the requirements for lifesaving appliances and communications of such craft. The

need for a study of this kind was indicated by information gathered by IMCO in regard to the operation of special and new design craft. It is noteworthy that the United States has submitted a proposed amendment to SOLAS 60 to permit the operation of experimental craft on international voyages to assist in furthering knowledge under operational conditions.

Information obtained by IMCO from member states and the International Organization for Standardization pointed to a need for further study of Regulation 22, Chapter II of SOLAS 60. Reports indicated a wide range of children's life jackets and minimum buoyancy allowed by various states. Recognizing the importance of this subject, the 4th Assembly approved the establishment of a Subcommittee on Life Jackets.

Recommendation 51 of SOLAS 60 said that IMCO should gather information concerning transmissivity and chromaticity as they effect ship's navigation lights and if necessary to initiate further studies on an international basis. Information has been provided by members and internaConsiderable tional organizations. work is being done on the subject by the Economic Commission for Europe which has produced a draft European Code for Inland Waterways that includes specifications for chromaticity and luminous intensity of lights. Because of its international implications this draft Code will have to be examined not only in regard to Recommendation 51 but also with respect to Recommendation 53 which recommends bringing local rules in as near agreement as possible with the international rules. The Assembly, therefore, approved the establishment of a Subcommittee on the Efficiency of Navigation Lights and Related Matters. However, due to the heavy work schedule this subcommittee will not be activated until 1967.

As can be seen from the foregoing IMCO has spent a very active year in furthering the tenets of its convention "to encourage the general adoption of the highest practicable standards in matters concerning maritime safety and efficiency of navigation". It has been stated that "The ship is the prime instrument of this ceaseless movement around the globe. . . . The ship carries both precious human lives and valuable cargo, and she represents a considerable capital sum; seaworthiness and safety of navigation are therefore imperative. Safety of the ship and safety of navigationthese are the aims to which the Intergovernmental Maritime Consultative Organization is devoted."