International law concerning the status and marking of remotely piloted aircraft.

Author:Henderson, Ian

    In recent times, significant media and legal attention has been paid to the use of remotely piloted aircraft (RPA) in areas such as Pakistan and Yemen. (1) The current terminology being used in the media and other areas debating this issue varies. As well as RPA (the current term being preferred in some military circles), other common terms include "drone", "armed drone", unmanned (or uninhabited) aerial vehicle (UAV), unmanned (or uninhabited) aircraft system (UAS); and when some form of armament is also involved, sometimes the word "combat" is after unmanned (or uninhabited), leading to the acronyms UCAS or UCAV. The legal issues discussed have generally concerned the use of force, the status of the operators of the aircraft (e.g., military or civilian intelligence agent), the status of the intended target, or the injury caused to someone and the damage caused to something other than the intended target. Comparatively little attention has been paid to legal issues concerning the aircraft themselves; however, the rise in the use and variety of RPA highlights some interesting legal issues concerning the aircraft themselves. This article looks at the international law concerning the "status" of RPA and the legal requirement, if any, for applying "markings" to RPA.

    While this article is concerned only with the aircraft, it is worth recalling that:

    Unmanned aircraft systems generally consist of (1) multiple aircraft, which can be expendable or recoverable and can carry lethal or nonlethal payloads; (2) a flight control station; (3) information and retrieval or processing stations; and (4) in some cases, wheeled land vehicles that carry launch and recovery platforms. (2) As for the RPA themselves:

    Over 1100 makes and models of unmanned aerial systems (UASs) are currently on the market or in development in more than 50 countries ... [involving] a diverse collection of fixed wing, rotorcraft, and lighter-than-air flying machines, available in a wide variety of sizes and capabilities. (3) The known technologies range from "micro" UAVs that are, in reality, flying robots designed to look and behave like a "bug," fit in the palm of a hand, and carry a high-resolution camera, to 25,000-pound turbojets with wingspans wider than a Boeing 737, operating at or above 60,000 feet at speeds in excess of 530 miles per hour for over 35 hours at a time. (4) Others designed for scientific research have flown as high as 100,000 feet and have stayed in the air for nearly three days without landing. (5) II. STATUS AND MARKING OF RPA: STATE AND CIVIL AIRCRAFT

    International law divides aircraft into two broad categories: state aircraft and civil aircraft. (6) The distinction between civil and state aircraft, albeit not always with the same terms, appears to date from the early 20th century. (7) A reference to state aircraft usually means, as a minimum, aircraft that are "used in military, customs and police services." (8) It is possible, though, to use the term "state aircraft" to mean all aircraft in the exclusive use or possession of a State and not be limited by the definition in the Chicago Convention. (9) As a result, there are two current views of which aircraft are state aircraft. One view is that despite the vague wording of the Chicago Convention, only military, customs and police aircraft may be state aircraft. (10) The other view is that other aircraft engaged in purely state activities (e.g. coast guard or search and rescue) may also be state aircraft. (11) Regardless of which position is correct, there are two main consequences that flow from being a state aircraft. First, state aircraft are not subject to the Chicago Convention, and particularly the detailed air navigation rules. Second, state aircraft enjoy certain immunities and rights. (12) There is no reason not to apply the same legal divisions and consequences to RPA as defined in the Chicago Convention. (13) So, while the Chicago Convention is not directly applicable to state aircraft (aside from article 3), there is no reason to treat RPA differently from "normal" state aircraft.

    No further requirements are specified in the Chicago Convention for an aircraft to have the status of a state aircraft. For example, no particular markings--national or otherwise--are specified. This is particularly noteworthy as article 20 of the Chicago Convention states: "Every aircraft engaged in international air navigation shall bear its appropriate nationality and registration marks." (14) However, the Chicago Convention applies to only civil aircraft and not to state aircraft. (15) Accordingly, the Chicago Convention does not require any particular markings, registration, etc., for state aircraft. (16) Interestingly, Article 10 of the 1919 Paris Convention stated: "All aircraft engaged in international navigation shall bear their nationality and registration marks...." (17) However, it is difficult to determine whether article 10 applied to state aircraft. This is because article 30 provided that: "All State aircraft other than military, customs and police aircraft shall be treated as private aircraft and as such shall be subject to all the provisions of the present Convention." (18) A clear inference from this provision is that the Paris Convention did not in general apply to certain types of state aircraft. (19)

    In a discussion of the criteria for determining whether an aircraft is a military versus a civil aircraft, Milde writes:

    This wording ["used" and "services"], in the absence of any other guidance, suggests that the drafters had in mind a functional approach to the determination of the status of the aircraft as civil and military: regardless of the design, technical characteristics, registration, ownership etc.; the status of the aircraft is determined by the function it actually performs at a given time. (20) Milde's argument and conclusion applies equally to other types of state aircraft. Williams adopts a similar position, stating that whether an aircraft is a state aircraft depends upon function, and not "design or technical characteristics, call sign, registration, or markings--all of which fall within the competence of its state of nationality." (21) Whether an aircraft is, for the purposes of the Chicago Convention, a state or civil aircraft, it is the "usage of the aircraft in question [that] is the determining criterion, and not, by themselves, other factors such as aircraft registration and markings...." (22)

    Notwithstanding that there appears to be no strict legal requirement for state aircraft to be marked as such, it often seems assumed that an aircraft will bear some sort of marking. (23) Other statements indicating an assumption of marking include: "state aircraft, including military aircraft, are also marked to indicate their nationality"; (24) and "state aircraft may include aircraft which, in light of their mission, display appropriate state markings...." (25)

    The importance of the expectations of States cannot be over emphasized. When one starts out with the somewhat ambiguous legal position expressed in article 3 of the Chicago Convention, (26) and the fact that States may essentially choose how to classify one another's aircraft, (27) then lack of markings only exacerbates the issue.

    Despite the aforementioned legal uncertainty, some general observations can be made. At a minimum, state aircraft include aircraft used in military, customs and police services. Whether an aircraft is being so used is primarily a functional test. (28) An aircraft need not bear markings to be a state aircraft, but absence of such markings is likely to prejudice the finding that the aircraft is a state aircraft by other States. RPA can be state aircraft and all of the proceeding points apply to RPA. A unique feature of RPA compared to manned aircraft is that RPA can be quite small in size. However, the relevant international law does not change. (29)


    While this article is not primarily concerned with the detail of the rights and liabilities of state aircraft, some discussion of the topic is important to illustrate the importance of determining whether an RPA is a civil or state aircraft. State aircraft enjoy certain rights and immunities, including immunity "from the jurisdiction of the courts of a territorial state." (30) The applicable law on a state aircraft is the jurisdiction, including criminal jurisdiction, of the "flag" State. (31) A significant immunity is that state aircraft are not subject to "foreign jurisdiction in respect of search and inspection" without consent. (32) Interestingly, the 1919 Paris Convention drew a distinction between types of state aircraft, with only military aircraft enjoying "the privileges which are customarily accorded to foreign ships of war"; (33) while other types of state aircraft did not enjoy such privileges. (34) Writing in 1970, Ward expressed doubt as to whether States would generally accept this principle with respect to military aircraft, (35) while a nearly contemporary writer seemed to be of the opposite view. (36) The better view today is that military aircraft enjoy sovereign immunity. (37) Further, such immunity applies to all types of state aircraft and not just those used in military, police and customs services. (38)

    Separate from the immunity issue is the issue of the rights enjoyed by state aircraft. For example, only certain types of aircraft may legally intercept suspected pirate ships and aircraft on or over the high seas...

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