Treaties, States Parties and Commentaries
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Commentary of 1987 
Light signal
    [p.1205] Annex I, Article 6 -- Light signal

    [p.1206] General remarks

    4153 Under Article 4, paragraph 2, of the draft regulations relating to medical transport by air in time of armed conflict drawn up in 1965 by the Commission m├ędico-juridique de Monaco, medical aircraft were to be provided "both by day and by night [...] with a fixed system of luminous visual signals". (1) In this connection, the technical experts consulted by the ICRC late in October 1970 proposed a flashing blue light as the distinctive light signal for medical aircraft. The signal was to be used both by day and by night.

    4154 As the colour white, red and green were used for navigation lights by all aircraft and vessels, in accordance with international air traffic and maritime navigation regulations, only the colour blue was still available for the distinctive light signal to be used by medical aircraft and other medical transports.

    4155 The chromatic limits of the blue light, which are set out in a publication of the International Commission on Illumination (CIE) (2) were communicated to the ICRC in January 1971 by the experts of the International Electrotechnical Commission (IEC) who took part in the 1970 consultation, in a commentary by the competent IEC Committee co-ordinated with the CIE Airborne Lighting Committee. (3)

    4156 flashing or winking light signals are easier to see than fixed lights of equal intensity, as day-to-day experience with road traffic hows. The flashing blue light is a recognized priority signal, set aside under national legislation in many countries as well as in nternational regulations (4) for use by ambulances (this term covers both civilian and military ambulances), police vehicles, fire brigade vehicles and possibly other special vehicles.

    4157 The blue light has also been used for some time by certain harbour, river or lake police craft. However, under the International Code of Signals which entered into force on 1 January 1986, it is allocated to vessels engaged in medical [p.1207] operations, namely, the hospital ships and medical craft protected by the Conventions and the Protocols, as well as rescue craft. (5)

    4158 These widespread and long-standing uses of the flashing blue light were not overlooked by the members of the Technical Sub-Commission at the Conference of Government Experts in 1972. (6) Nevertheless, it was proposed that this light should be used as the distinctive signal of medical aircraft, since it was not already being used for air navigation. The colour blue is used to mark airfield taxiways, but the lights in question are fixed luminous beacons. As far as other means of medical transport are concerned, paragraph 3 of this article leaves the possibility open of reserving the use of this light signal for the identification of such transports in time of armed conflict, by day and by night. Thus Article 6 of Annex I is in line with Article 18 ' (Identification) 'of the Protocol, which is concerned with medical transports in general.

    Paragraph 1

    4159 In draft Annex I, Article 8, paragraph 1, the flashing blue light was defined in terms of the frequency of its flashes, namely, between forty and one hundred per minute. Its exclusive use by medical aircraft was not specified.

    4160 The ICRC's draft was amended by the Technical Sub-Committee at the first session in 1974; Article 8 became Article 7 and the new text of paragraph 1 referred to the use of the blue light by medical aircraft subject to the provisions of new paragraph 3, which was concerned with the special agreement that might be concluded between the Parties to the conflict regarding the use of the same blue light by other types of medical transport.

    4161 Paragraph 1 was recast in its final form by the Technical Sub-Committee at the second session in 1976, when the flashing rate of the blue light was altered and the reference to paragraph 3 deleted.

    4162 Under Article 18 ' (Identification), ' paragraph 8, of the Protocol, the use of distinctive signals is subject to the same supervision as that of the distinctive emblem. Therefore, Article 44 of the First Convention is applicable to distinctive signals, including the flashing blue light used by ambulances or medical helicopters. If authorized by the competent authority, therefore, the flashing blue light could be used by aircraft in peacetime in accordance with Article 44 , subject to the relevant ICAO regulations. (7)

    4163 The trichromatic co-ordinates given in this paragraph define the boundaries of the blue colour. These boundaries are straight lines separating the blue zone from the other colour zones on the CIE's chromatic diagram, which represents a triangular surface showing the recommended boundaries of the colours used for light signals -- red, orange, yellow, green, blue, violet -- arranged in contiguous [p.1208] zones round a white centre (cf. document annexed No. 1, p. 1212); (8) document annexed No. 2 shows the recommended boundaries for the blue and violet signals. For technical reasons, the boundaries on the colour diagram reproduced below as an illustration are only approximate (cf. documents annexed Nos. 2 and 3, p. 1213 and p. 1214).

    4164 The recommended flashing rate -- between sixty and one hundred flashes per minute -- is the same as that laid down by ICAO for the anti-collision lights of civilian aircraft. Consequently, luminous signalling by means of the flashing blue light looks very simple in theory. A medical aircraft could seemingly be marked very quickly with a blue light by replacing the red glass covers of the anti-collision lights by blue glass or plastic covers. In practice, however, the operation is more complex, as has been demonstrated by tests conducted using ICRC aircraft. The main difficulties encountered are as follows:

    a) The rotating anti-collision light fittings in civilian and military aircraft are not standardized, varying in size from one plane to another depending on the manufacturer.
    b) The specially manufactured heat-resistant blue glass or plastic domes are not universally available; they have to be ordered and checked for heat-resistance, in view of the large amount of heat energy retained by the colour blue.
    c) The installation on a medical aircraft of blue lights of the same type as those used by road vehicles raises problems of electricity supply and compliance with aeronautical standards. A light of this type fitted under the fuselage of a Piper Cherokee Six aircraft protruded too much and was smashed by stones and lumps of earth when taking off from an improvised runway.
    d) The ICRC has also tested blue lights of the "strobe" type, that is, lights in which electricity is discharged in a gas. Lights of this type fitted to ICRC aircraft were shown to have the following disadvantages:
    -- the intensity of the flashes produced may interfere with the piloting of the aircraft or helicopter (reflection on the rotor blades); electromagnetic interference makes it necessary to shield navigational and communication equipment;
    -- beyond a few hundred metres, the strobe light loses its blue colour and is seen from the ground as white. Seen from the front, a medical aircraft emitting rapid flashes of blue-white light may look like a military aircraft machine-gunning the ground, the flashing light resembling gunfire. An ICRC Piper Cherokee actually experienced this difficulty; it was fired on by guerrilla fighters who explained later that they had been misled by the flashing strobe light.

    4165 A solution therefore has to be worked out with the manufacturers of aeronautical equipment, one of whom has expressed misgivings about the intensity required to distinguish the flashing blue light used by medical aircraft from the flashing blue-white strobe lights more and more commonly used as [p.1209] anti-collision lights in addition to the red rotating lights. He claimed that rather more than 1000 watts would be required to produce effective intensity of 100 candelas on a quasi-horizontal plane. Such highly-powered electric flashes raise problems for the aircraft's power supply system.

    4166 The ICRC has established regular contacts with both ICAO and manufacturers regarding the technical problems caused by the flashing blue light. ICAO has requested that the following parameters be specified:

    -- the required intensity of the flashing blue light;
    -- the required visual range, weather conditions, background;
    -- the required beamwidth and intensity in the angles of vision above and below the horizontal plane.

    4167 The flashing blue light should be tested again using special blue glass covers, and the results communicated to ICAO.

    4168 Medical helicopters based on board hospital ships at sea have to be identifiable from greater distances than on land. Experiments at sea have demonstrated that an airborne medical helicopter showing all its navigation and landing lights is visible from a long way off. Here too, studies should continue to be conducted, particularly by the maritime States concerned. (9) The visual or luminous range of the light, expressed in nautical miles as a function of its intensity in terms of candelas, may be calculated using the formula in Annex I to the Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREG 1972). (10)

    Paragraph 2

    4169 According to the type of medical aircraft used, one or more blue lights should be fitted so that the light signal is visible in every direction. If placed on the top of the tail fin, the signal may be omnidirectional but it will not be easily accessible on a large aircraft. In the case of a small aircraft or helicopter, a flashing blue light should be placed both underneath and atop the fuselage.These lights must not interfere with the piloting of the aircraft, either by day or by night.

    4170 Additional lights can only be installed on aircraft by firms specializing in aeronautical maintenance (supplies, positioning, power supply, aircraft structure, light casing, wiring, switches).

    4171 In the case of permanent military medical aircraft, this operation should be carried out in peacetime unless it is possible to replace the red cover by a blue one in the event of an emergency. In all cases, steps must be taken to ensure that the blue light can be seen at maximum intensity in all directions, a requirement which does not apply to ordinary anti-collision lights meeting ICAO specifications. [p.1210] Anti-collision lights have to be visible in all directions but their intensity must be variable in relation to the horizontal plane, whereas the intensity of the flashing blue light should be at its highest when seen from all angles, both above and below the horizontal plane.

    4172 No international regulations concerning the flashing blue light used by civilian medical aircraft have yet been published. When ICAO is in possession of the necessary information on the flashing blue light, it will be able to make proposals to the Air Navigation Commission for the amendment of Annexes 2, 6 and 8 and of the Airworthiness Technical Manual. (11) Satisfactory follow-up action will then have been taken in respect of Resolution 17 addressed to ICAO by the Diplomatic Conference.

    Paragraph 3

    4173 The established practice of using the flashing blue light as a priority signal in road traffic and on board certain types of craft prevented the Diplomatic Conference from reserving it for the exclusive use of medical vehicles, hospital ships and coastal rescue craft. For this reason, paragraph 3 provides for a special agreement to be concluded between the Parties to the conflict regarding the use of the flashing blue light by medical vehicles and hospital ships. However, new Chapter XIV of the International Code of Signals which entered into force on 1 January 1986 provides for the use of the flashing blue light by hospital ships, coastal rescue craft and medical aircraft. This provision meets the request addressed by the Diplomatic Conference to the International Maritime Organization in Resolution 18.

    4174 Paragraph 4.2 of the above-mentioned Chapter XIV stipulates that the visual range of the flashing blue light shall be as high as possible and not less than three nautical miles, in accordance with Annex I to the International Regulations for Preventing Collisions at Sea, 1972. (12) Tests carried out at sea have shown that, ideally, a hospital ship's flashing blue light should be identifiable at a distance of about ten nautical miles. Further research is still required in this connection. (13)

    4175 The International Life-Boat Conference (ILC) is justifiably concerned about the safety of coastal rescue craft in time of armed conflict. It would like such craft -- together with their crews, land-based installations and personnel -- to enjoy the same protection as that afforded to hospital ships and their crews. This claim for [p.1211] protection has been approved by official or officially recognized private maritime rescue organizations; the rescue organizations of the major maritime States belong to the ILC. As far as marking and identification are concerned, new Chapter XIV meets the requirements of the maritime rescue organizations. The flashing blue light is to be used by rescue craft as a distinctive light signal in time of armed conflict; it is also to be used in peacetime so that the shipwrecked and those in distress at sea can see it from afar and know that rescue is at hand. (14)

    4176 The agreement between the Parties to the conflict reserving the use of the flashing blue light for the identification of medical vehicles, namely, permanent or temporary civilian and military ambulances, should not give rise to any difficulty, since this light signal is already used in peacetime by civilian or military ambulances in many countries.

    4177 In periods of armed conflict it is not really in the interest of vehicles which are not protected by the Conventions and their Protocols to attract attention by using any type of coloured light signal at all. Accordingly, any such vehicle using a blue light in peacetime could probably refrain from doing so, in favour of the ambulances.

    ' Ph. E. '

    Documents annexed (cf. supra, p. 1208)

    ' CIE chromaticity diagrams '

    Document No. 1. Recommended boundaries for light signals

    Document No. 2. Recommended boundaries for blue and violet light signals

    Document No. 3

    ' Standardized colour table ', based on the chromaticity diagram (colour triangle) of the International Commission on Illumination (CIE) and DIN Standard 5033

    The colours of luminous sources and surfaces (i.e. paints, colour filters, etc) are arranged clearly on this diagram according to their chromaticity. This arrangement of the colours presupposes a previous measurement of the chromaticity coordinates x and y; these coordinates in fact determine the colour point of a certain chromaticity. The luminance of light sources or the luminance factor of surface colours are not represented on this diagram. Each point of the chromaticity diagram represents a chromaticity; colours of the same chromaticity differ from each other only through their luminosity. In the centre of the triangle (exactly at the point x = 0.333 and y = 0.333) is the achromatic area (white, grey down to black depending on the luminosity). The border is composed of the spectrum locus and of the so-called purple boundary; a few wave lengths are indicated along the spectrum locus (in nm). All other colours are situated between the achromatic point and the border line, and all the straight lines originating from the achromatic point have the same hue, with increasing saturation. The chromaticity of an additive mixture of colour stimuli of two components is located, on the colour triangle, always on the straight line connecting the chromaticity of the components; the chromaticity diagram rests on this principle. Note: This representation of the chromaticity diagram shows only approximately the distribution of the chromaticities. A perfect concordance of the colours of the diagram with the exact chromaticity of definite points cannot be attained because of technical printing reasons (translation from German by M. Dutruit).

    NOTES (1) [(1) p.1206] CE/7b, pp. 60-61, Art. 4; pp. 50-52. Cf. E. Evrard, op. cit;

    (2) [(2) p.1206] CIE, publication No. 2.2 (TC-1.6), 1975, "Colours of Light Signals", pp. 1-28; p. 24, Fig. 1; p.
    28, Fig. 5;

    (3) [(3) p.1206] CIE, Committee E-1.7, Fundamentals of Visual Signalling, in CE 1972, ' Technical Memorandum ', p. 41, Annex I;

    (4) [(4) p.1206] United Nations Economic and Social Council, Economic Commission for Europe, Inland Transport Committee, Working Party on Road Transport, consolidated resolution on road traffic (R.E.I.), para. 2.3, Marking of priority vehicles, TRANS/SC 1/294/Rev.3/Amend. 1 (1981); id., Group of Experts on the Construction of Vehicles, Regulation "Uniform provisions concerning the approval of warning lamps for motor vehicles", TRANS/SC 1/WP 29/12, para. 24 and TRANS/SC 1/WP 29/79, para. 82 (entry into force in 1986);

    (5) [(5) p.1207] IMO, ' International Code of Signals ', London, 1985, Chapter XIV;

    (6) [(6) p.1207] ' CE 1972, Report ', Vol. I, p. 55, para. 11; p. 57, Section VI;

    (7) [(7) p.1207] Cf. commentary Art. 18, para. 7, Protocol, supra, p. 233, and ICAO, Doc. 9051-AN/896, Airworthiness Technical Manual, Part III, Section 8;

    (8) [(8) p.1208] CIE publication No. 2.2 (TC-1.6), 1975, "Colours of Light Signals", is trilingual (English, French and German); the colours themselves are not reproduced in it, cf. documents annexed;

    (9) [(9) p.1209] Cf. Ph. Eberlin, "The Identification of Medical Aircraft...", op. cit.; id., "Identification of Hospital Ships...", op. cit., pp. 321-323;

    (10) [(10) p.1209] IMO, ' International Conference on Revision of the International Regulations for Preventing Collisions at Sea, ' 1972, London, 1974 ed., reprinted in 1983. In this connection, see also the IEC communication in Annex I to CE 1972, Technical Memorandum, p. 41;

    (11) [(11) p.1210] ICAO, Annex 2, ' Rules of the Air, ' seventh ed., Montreal, July 1981. ICAO, Annex 6, ' Operation of Aircraft, ' Part I, fourth ed., Montreal, July 1983; Part II, third ed., Montreal, September 1983. ICAO, Annex 8, ' Airworthiness of Aircraft, ' sixth ed., Montreal, July 1973. ICAO, Doc. 9051-AN/896, ' Airworthiness Technical Manual, ' first ed., Montreal, 1974. ICAO, Doc. 9110, ' ICAO Lexicon, ' Vol. I, ' Vocabulary; ' Vol. II, Definitions, fourth ed., Montreal, 1974;

    (12) [(12) p.1210] Cf. IMO, ' International Code of Signals ', Chapter XIV, annexed, supra, p. 1170. Cf. footnote 9, supra;

    (13) [(13) p.1210] Cf. Ph. Eberlin, "Identification of Hospital Ships...", op. cit., visibility of the blue light at sea, p. 322; blue light similar to those used on police cars, identifiable to the naked eye at a distance of 3 miles and with binoculars at a distance of 7 miles;

    (14) [(14) p.1211] Cf. G. Gidel, op. cit.; Ph. Eberlin, "The Protection of Rescue Craft in Periods of Armed Conflict", ' IRRC, ' May-June 1985, p. 140;