Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 29. Medical Transports
Section B. Respect for and protection of medical aircraft
The UK Military Manual (1958) restates the rules on medical aircraft found in Article 36 of the 1949 Geneva Convention I and Article 22 of the 1949 Geneva Convention IV. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, §§ 34 and 358–359.
The UK LOAC Pamphlet (1981) provides:
Helicopters are increasingly used for the evacuation of the wounded. Medical aircraft are protected in the same way as other medical transports, but, having regard to the range of anti-aircraft missiles, the problems of identification are greater. Overflight of enemy-held territory without prior agreement will mean loss of protection. Medical aircraft must obey summonses for inspection. Protocol I contains detailed new rules on medical aircraft and provides for light and radio recognition signals. 
United Kingdom, The Law of Armed Conflict, D/DAT/13/35/66, Army Code 71130 (Revised 1981), Ministry of Defence, prepared under the Direction of The Chief of the General Staff, 1981, Section 6, p. 24, § 12.
The UK LOAC Manual (2004) states:
7.12. Medical transport means any means of transportation, whether military or civilian, permanent or temporary, assigned exclusively to the conveyance by land, water or air of the wounded, sick, shipwrecked, medical or religious personnel, medical equipment or medical supplies protected by the Geneva Conventions and Additional Protocol I and under the control of a competent authority of a party to the conflict. In Additional Protocol I, reference to “medical vehicles” expressly means “any medical transports by land”. Similarly, “medical ships and craft” means “any medical transports by water” and “medical aircraft” means “any medical transports by air”.
7.12.1. The assignment to medical purposes must be exclusive, although it may be permanent or temporary. The word “exclusive” is intended to restrict the definition of medical transport and its use so that the essential protection will not be eroded by abuses. “Permanent” means for an indeterminate period; “temporary” means limited periods but devoted exclusively to medical tasks during the whole of such periods.
Medical aircraft
7.22. Aircraft duly assigned to medical purposes, flying in combat zones are protected as soon as they are recognized as such. Medical aircraft flying over areas physically controlled by an adverse party, or over areas the control of which is not clearly established, may be ordered to land or to alight on water as appropriate to permit inspection. Medical aircraft must obey such orders. They must be given reasonable time for compliance but in default of such obedience the aircraft may be attacked. In all cases, protection for medical aircraft can be fully effective only by prior agreement between the competent military authorities of the parties to the conflict. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 7.12–7.12.1 and 7.22.
In its chapter on air operations, the manual states:
12.28. The following classes of enemy aircraft are exempt from attack:
a. medical aircraft;
b. aircraft granted safe conduct by agreement between the parties to the conflict; and
c. civil airliners.
Conditions of exemption for medical aircraft
12.29. Medical aircraft are exempt from attack only if they:
a. have been recognized as such;
b. are acting in compliance with an agreement as specified in paragraph 12.112;
c. fly in areas under the control of own or friendly forces; or
d. fly outside the area of armed conflict.
12.29.1. In other instances, medical aircraft operate at their own risk.
Conditions of exemption for aircraft granted safe conduct
12.30. Aircraft granted safe conduct are exempt from attack only if they:
a. are innocently employed in their agreed role;
b. do not intentionally hamper the movements of combatants; and
c. comply with the details of the agreement, including availability for inspection.
Conditions of exemption for civil airliners
12.31. Civil airliners are exempt from attack only if they:
a. are innocently employed in their normal role; and
b. do not intentionally hamper the movements of combatants.
Loss of exemption
12.32. If aircraft exempt from attack breach any of the applicable conditions of their exemption as set forth in paragraphs 12.29 to12.31, they may be attacked only if:
a. diversion for landing, visit and search, and possible capture, is not feasible;
b. no other method is available for exercising military control;
c. the circumstances of non-compliance are sufficiently grave that the aircraft has become, or may be reasonably assumed to be, a military objective; and
d. the collateral casualties or damage will not be disproportionate to the military advantage gained or anticipated.
12.33. In case of doubt whether a vessel or aircraft exempt from attack is being used to make an effective contribution to military action, it shall be presumed not to be so used. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 12.28–12.29.1 and 12.30–12.33.
The manual further states:
12.93. The following aircraft are exempt from capture:
a. medical aircraft; and
b. aircraft granted safe conduct by agreement between the parties to the conflict.
12.94. Aircraft listed in paragraph 12.93 are exempt from capture only if they:
a. are innocently employed in their normal role;
b. do not commit acts harmful to the enemy;
c. immediately submit to interception and identification when required;
d. do not intentionally hamper the movement of combatants and obey orders to divert from their track when required; and
e. are not in breach of a prior agreement. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 12.93–12.94.
The manual defines medical aircraft as follows:
The term “medical aircraft” is defined as any means, whether service or civilian, of conveying by air the wounded, sick, shipwrecked, medical personnel, religious personnel, medical equipment or medical supplies protected by the Geneva Conventions and Additional Protocol I. Whether assigned on a permanent or temporary basis, such an aircraft must be assigned exclusively to that purpose and must be under the control of a competent authority of a party to the conflict. The term “shipwrecked” includes personnel in the sea or other waters after forced landing by or from aircraft. Helicopters used for medical purposes within the above conditions come within the definition of medical aircraft. Hovercraft do not. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 12.104.
On the protection of medical aircraft, the manual states:
12.110. In and over land areas physically controlled by friendly forces, or in and over sea areas not physically controlled by an adverse party, the respect and protection of medical aircraft of a party to the conflict is not dependent on any agreement with an adverse party.
12.110.1. Where, however, proposed flight plans of medical aircraft will bring them within the range of an adverse party’s surface to air weapons systems it is only sensible for the party operating the aircraft to notify the adverse party. In any circumstances, specific agreement between the adversaries, and any other states involved, is, in practice, the most effective guarantee of the safety of medical aircraft.
Contact and similar zones
12.111. In and over those parts of the contact zone which are physically controlled by friendly forces and in and over those areas the physical control of which is not clearly established, protection for medical aircraft can only be effective in so far as this has been agreed in advance by the parties. In the absence of an agreement medical aircraft operate at their own risk but they must nevertheless be respected when recognized.
12.111.1. The “contact zone” is any area on land where the forward elements of opposing forces are in contact with each other, especially where they are exposed to direct fire from the ground.
Areas controlled by an adverse party
Prior agreement
12.112. Medical aircraft continue to be protected whilst flying over land or sea areas physically controlled by an adverse party so long as there are prior agreements to that effect. Parties to the conflict are encouraged to notify such flights and to conclude such agreements, particularly in areas where control is not clearly established. Agreements should specify the altitudes, times and routes for safe operation and should include means of identification and communications.
12.112.1. A medical aircraft which flies over an area physically controlled by an adverse party either without prior agreement or in breach of the terms of an agreement, either through navigational error or because of an emergency affecting the safety of the flight, must make every effort to identify itself and to inform the adverse party of the circumstances. As soon as a medical aircraft has been recognized by an adverse party, that party is to make all reasonable efforts to give the order to land or to alight on water for inspection, or to take other measures to safeguard its own interests. In any case, the aircraft concerned must be allowed time for compliance before it is attacked. It is likely that any such agreement would be for a specific flight or series of flights rather than a general agreement lasting for a period of time. The necessity for having an agreement and adhering rigidly to its terms cannot be over-stressed. A medical aircraft, no matter how well-marked and in how many ways it indicates its status, which enters enemy airspace without agreement or in breach of the terms of an agreement is at risk of attack even if it has been recognized as claiming medical status. Before attacking, an adverse party must make all reasonable efforts to give the order to land or alight on water for inspection. This obligation arises only where there has been navigational error or an emergency affecting the safety of the flight and the circumstances have been communicated to the adverse party.
Absence of prior agreement
12.113. Whether a belligerent orders a medical aircraft to land for inspection or takes other measures to safeguard its interests, for example, ordering a change of route, an increase in altitude or requesting more information about the nature of the medical aircraft’s difficulties, it must allow that aircraft time for compliance before attacking. The degree of deviation from an agreement or from instructions that an enemy may claim as justification for an attack might be very slight. The captain of a medical aircraft must take great care to ensure that his aircraft does not enter enemy airspace without prior agreement and that, when it does enter by agreement, that the terms of the agreement are closely adhered to. The captain of a medical aircraft who finds that his aircraft has strayed into enemy airspace must make every effort to identify his aircraft to the enemy and to indicate his submission to that adverse party’s air traffic instructions. If, owing to an emergency, it is necessary to enter enemy airspace without prior agreement or contrary to the terms of an agreement, contact should, if possible, be made with the enemy in order to obtain agreement to the proposed course of action.
Medical aircraft in neutral airspace
12.114. Belligerent medical aircraft shall not enter neutral airspace except by prior agreement. When within neutral airspace pursuant to agreement, medical aircraft shall comply with the terms of the agreement. The terms of the agreement may require the aircraft to land for inspection at a designated airport within the neutral state. Should the agreement so require, the inspection and follow-on action shall be conducted in accordance with paragraphs 12.115 to 12.116.
12.115. Should a medical aircraft, in the absence of an agreement or in deviation from the terms of an agreement, enter neutral airspace, either through navigational error or because of an emergency affecting the safety of the flight, it shall make every effort to give notice and to identify itself. Once the aircraft is recognised as a medical aircraft by the neutral state, it shall not be attacked but may be required to land for inspection. Once it has been inspected, and if it is determined in fact to be a medical aircraft, it shall be allowed to resume its flight.
12.116. If the inspection reveals that the aircraft is not a medical aircraft, it may be captured, and the occupants shall, unless agreed otherwise between the neutral State and the parties to the conflict, be detained in the neutral State where so required by the rules of international law applicable in armed conflict, in such a manner that they cannot again take part in the hostilities.
Summary of rules
12.117. The rules that must be observed by the captain of a medical aircraft in relation to overflight of the territory of an adverse party may be summarized as follows:
a. no overflying without agreement;
b. where there is an agreement, its terms must be adhered to strictly;
c. there must be no deviation from the terms of an agreement for any reason other than an emergency affecting the safety of the flight;
d. if there is accidental overflight, in the absence of an agreement, every effort must be made to contact the adverse party, to identify the aircraft, its status and the circumstances of its flight and to submit to the adverse party’s air traffic instructions;
e. if an emergency affecting the safety of a flight necessitates overflying without agreement or in breach of an agreement, every attempt must be made to inform the adverse party and to seek its agreement. If times does not permit this course of action, a medical aircraft may proceed but must identify itself and its status to the adverse party and must immediately notify the adverse party of the circumstances and proposed course of action; and
f. the adverse party’s instructions, including instructions to land, must be obeyed.
Interception of enemy medical aircraft
12.118. If there is no agreement concerning the operation of an apparent enemy medical aircraft and it fails to respond to instructions then, if it constitutes an immediate military threat and other methods of control are impracticable, it may be attacked. Similarly, an apparent medical aircraft may be attacked if it is beyond reasonable doubt that its claim to protection is unjustified or indeed if it initiates an attack.
12.118.1. Any attack on an enemy aircraft recognized as claiming medical status should be instituted only as a last resort. If a purported medical aircraft is not known to be engaged in any activity inconsistent with medical status and obeys the instructions of its interceptor, it must not be attacked even if there has been no prior agreement as to its activity. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 12.110–12.118.1.
Regarding restrictions on the use of medical aircraft, the manual states:
12.119. Parties to an armed conflict must not use medical aircraft in an attempt to acquire a military advantage. Their presence must not be used in an attempt to render military objectives immune from attack.
12.119.1. For example, areas where medical aircraft are loaded or unloaded, including helicopter pads, should be as far away as practicable from areas of normal military operations. Medical aircraft should not be parked adjacent to buildings or other installations which themselves are not entitled to protection.
Intelligence
12.120. Medical aircraft must not be used to collect or transmit intelligence data or carry any equipment intended for such purposes. The persons and cargo that may be carried by medical aircraft are restricted to the wounded, sick, shipwrecked, medical and religious personnel and medical supplies. Personal effects and equipment intended solely to facilitate navigation, communication or identification are permissible.
12.120.1. The presence of communications and encryption equipment in an aircraft operating as a medical aircraft is not precluded. Nor is the use of such equipment wholly to facilitate navigation, identification and communication in support of the operation of medical aircraft. Neither such presence nor such use negates the protection to which the medical aircraft is entitled.
Arms
12.121. Medical aircraft must not carry any armament. However, small arms and ammunition collected from the wounded, sick and shipwrecked on board and not yet handed over to the proper service authority, together with such light individual weapons as may be necessary to enable medical personnel on the aircraft to defend themselves and the wounded, sick and shipwrecked in their charge, are permissible.
Search and rescue
12.122. Whilst flying over contact or similar zones or over areas controlled by an adverse party, medical aircraft must not, without prior agreement with the adverse party, be used to search for the wounded, sick and shipwrecked.
12.122.1. This restriction does not relate to the use of medical aircraft for such search purposes in areas controlled by friendly forces or not physically controlled by an adverse party. In these circumstances, the medical aircraft is, when recognized, entitled to protection.
12.122.2. An agreement to operate medical aircraft in a search and rescue role will be more readily achieved following a specific engagement when search and rescue is considered necessary. A speculative search and rescue operation when there are no known casualties is more likely to be construed as a reconnaissance exercise and an agreement is thus less likely to be achieved. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 12.119–12.122.2.
[emphasis in original]
In a footnote to paragraph 12.120.1, the manual states:
On ratification of [the 1977 Additional Protocol I], the UK made the following statement: “given the practical need to make use of non-dedicated aircraft for medical evacuation purposes, the UK does not interpret this paragraph as precluding the presence on board of communications equipment and encryption materials or the use thereof solely to facilitate navigation, identification or communication in support of medical transportation”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 12.120.1, footnote 162.
Regarding the landing and inspection of medical aircraft, the manual states:
12.125. A medical aircraft flying over areas which are either physically controlled by an adverse party or over which physical control has not been clearly established may be ordered to land for inspection. Medical aircraft must obey such an order.
12.125.1. Whether a medical aircraft has landed in response to such an order or whether it has landed for other reasons, an inspection must be commenced without delay and must be conducted expeditiously. The party carrying out the inspection may not order the removal of the wounded and sick from the aircraft unless their removal is essential for the inspection. It must, in any event, ensure that the condition of the wounded and sick is not adversely affected by the inspection or the removal. Although there is no provision prohibiting the removal of crews, the medical attendants or medical supplies from the aircraft during the inspection, the inspection should be carried out as expeditiously as possible and with the minimum of inconvenience and should be carried out in a reasonable and unprovocative manner always bearing in mind the humanitarian mission of the aircraft involved.
Medical status confirmed
12.126. If the inspection discloses that an aircraft:
a. is a medical aircraft as defined in paragraph 12.104;
b. has not violated any of the restrictions set out in paragraphs 12.119–12.121 [relating to military advantage, intelligence, arms, and search and rescue]; and
c. has not flown without, or in breach of, a prior agreement where such an agreement is required …
the aircraft and those of its occupants who belong to the adverse party operating the aircraft or to a neutral state or other state which is not a party to the conflict must be allowed to continue the flight without further delay.
Medical status not confirmed
12.127. If, however, an inspection discloses that an aircraft:
a. is not a medical aircraft as defined in paragraph 12.104;
b. has violated any of the restrictions set out in paragraphs 12.119–12.121 [relating to military advantage, intelligence, arms, and search and rescue]; or
c. has flown without, or in breach of, a prior agreement where such an agreement is required …
the aircraft may be seized. A seized aircraft that has been assigned as a permanent medical aircraft may be used thereafter by the capturing power as, and only as, a medical aircraft. Each occupant of the aircraft is treated according to his status. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 12.125–12.127.
Upon ratification of the 1977 Additional Protocol I, the United Kingdom declared with respect to Article 28(2):
Given the practical need to make use of non-dedicated aircraft for medical evacuation purposes, the United Kingdom does not interpret this paragraph as precluding the presence on board of communication equipment and encryption materials or the use thereof solely to facilitate navigation, identification or communication in support of medical transportation as defined in Article 8 (f). 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § (e).