For an aerial blockade to be considered effective under Rule 151, it is required that civilian aircraft believed on reasonable grounds to be breaching, or attempting to breach, an aerial blockade, be forced to land, inspected, captured or diverted. If civilian aircraft clearly resist interception, an order to land and capture, they are at risk of attack after prior warning. As for civilian airliners, Section J applies.
- It follows from the reference to Rule 151 in the introductory sentence of Rule 156 that a Blockading Party must take action with a view to preventing access to, or exit from, the blockaded area. If the Blockading force decides to remain inactive, the aerial blockade is no longer effective and becomes invalid.
- The wording of the first sentence of Rule 156 does not necessarily imply that interception is mandatory. The important factor is that a civilian aircraft suspected of breaching an aerial blockade, will be “forced to land, inspected, captured, or diverted”. This may be done without prior interception.
- Since neutral civilian aircraft are obliged to respect an aerial blockade that conforms to the legal requirements of publicity and effectiveness, they become liable to inspection, capture or diversion. A breach of an aerial blockade — inbound or outbound — occurs at the moment an aircraft crosses the outer limit of the blockaded area as defined in the respective declaration (see Rule 148).
- An attempt to breach an aerial blockade only occurs in either of the following two sets of circumstances: (i) if an aircraft takes off in the blockaded area with a course evidently set in the direction of the outer limit of the blockaded area; or (ii) if it is in international airspace and clearly on a route destined for the blockaded area.
- Reasonable grounds for concluding that a breach, or attempt to breach, of an aerial blockade has occurred exist if a neutral civilian aircraft that has been summoned (i) gives false information as to its cargo or destination; or (ii) it lingers in the vicinity of the blockaded area, thus leading to reasonable grounds to suspect that it intends to cross the blockade line as soon as the patrol aircraft have left the respective airspace.
- Liability to capture presupposes knowledge of the existence of the aerial blockade. That knowledge may be actual or presumptive. The Blockading Party may rely on an assumption that neutral aviation has acquired the knowledge from a NOTAM, if issued (see Rule 148 (in particular Rule 148 (c)) and Rule 149).
- If a neutral aircraft approaches the blockaded area in ignorance of the aerial blockade (in particular when no NOTAM has been issued), the aircraft must be informed individually about the existence of the aerial blockade by an officer of the Blockading Party (see Art. 16 of the 1909 London Declaration). This can be done through establishing radio communication with the aircraft concerned.
- If civilian aircraft “clearly resist” interception, they become military objectives and are at risk of attack after prior warning (an attack against a civilian aircraft under such circumstances may offer a definite military advantage, since this may be the only means of preserving the effectiveness of the aerial blockade). As for enemy civilian aircraft, see Rule 27 (d). As for neutral civilian aircraft, see Rule 174 (e). As for civilian airliners (be they enemy or neutral), see Rule 63 (e).
- If a civilian aircraft is trying to escape, the escaping aircraft may be pursued by the intercepting military aircraft. As long as the pursuit is not abandoned (“hot pursuit”), it remains at risk of attack. The pursuit will be sufficiently “hot” if the escaping aircraft is continuously tracked by the military aircraft of the Blockading force, such as an AWACS that is an integral part of the Blockading Party. Pursuit must be abandoned as soon as the neutral civilian aircraft enters neutral airspace.
- Since capture is but a means to effectively enforce an aerial blockade, punitive aims may not be pursued. Hence, a civilian aircraft which has successfully escaped capture may not be captured later for the sole reason of having breached, or attempted to breach, an aerial blockade in the past.
- As regards capture of, and attacks on, civilian airliners, see Section J (I) and Section J (III).
- Art. 14 of the 1909 London Declaration: “The liability of a neutral vessel to capture for breach of blockade is contingent on her knowledge, actual or presumptive, of the blockade.”
Art. 15 of the 1909 London Declaration: “Failing proof to the contrary, knowledge of the blockade is presumed if the vessel left a neutral port subsequently to the notification of the blockade to the Power to which such port belongs, provided that such notification was made in sufficient time.”
- Art. 16 of the 1909 London Declaration: “If a vessel approaching a blockaded port has no knowledge, actual or presumptive, of the blockade, the notification must be made to the vessel itself by an officer of one of the ships of the blockading force. This notification should be entered in the vessel’s logbook, and must state the day and hour, and the geographical position of the vessel at the time. If through the negligence of the officer commanding the blockading force no declaration of blockade has been notified to the local authorities, or, if in the declaration, as notified, no period has been mentioned within which neutral vessels may come out, a neutral vessel coming out of the blockaded port must be allowed to pass free.”