Related Rule
Australia
Practice Relating to Rule 7. The Principle of Distinction between Civilian Objects and Military Objectives
Section E. Attacks against civilian means of transportation
Australia’s Commanders’ Guide (1994) states:
Civilian vessels, aircraft, vehicles and buildings may be lawfully attacked if they contain combatant personnel, military equipment, supplies or are otherwise associated with combat activity inconsistent with their civilian status. 
Australia, Law of Armed Conflict, Commanders’ Guide, Australian Defence Force Publication, Operations Series, ADFP 37 Supplement 1 – Interim Edition, 7 March 1994, § 951.
Australia’s Defence Force Manual (1994) states:
Civil aircraft in flight (including state aircraft which are not military aircraft) should not be attacked. They are presumed to be carrying civilians who may not be made the object of direct attack. If there is doubt as to the status of a civil aircraft, it should be called upon to clarify that status. If it fails to do so, or is engaged in non civil activities, such as ferrying troops, it may be attacked. Civil aircraft should avoid entering areas which have been declared combat zones by the belligerents.
Civil aircraft which have been absorbed into a belligerent’s air force and are being ferried from the manufacturer to a belligerent for this purpose, may be attacked. 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, §§ 852 and 853.
Australia’s LOAC Manual (2006) states in its chapter on “Maritime Operations”:
6.39 Enemy merchant vessels. Enemy merchant vessels may only be attacked if they meet the definition of military objective.
6.40 Enemy civil aircraft. Enemy civil aircraft may likewise only be attacked if they meet the definition of a military objective.
6.44 Classes of vessels exempt from attack. The following classes of enemy vessels are exempt from attack:
• passenger vessels when engaged only in carrying civilian passengers;
6.56 The destruction of enemy passenger vessels carrying only civilian passengers is prohibited at sea. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, §§ 6.39, 6.40, 6.44 and 6.56.
In its chapter on “Air Operations”, the manual states:
8.56 Civil aircraft in flight (including state aircraft, which are not military aircraft) should not be attacked. They are presumed to be carrying civilians who may not be made the object of direct attack. If there is doubt as to the status of a civil aircraft, it should be called upon to clarify that status. If it fails to do so, or is engaged in non-civil activities, such as ferrying troops, it may be attacked. Civil aircraft should avoid entering areas that have been declared conflict zones by the belligerents.
8.57 Civil aircraft, which have been absorbed into a belligerent’s air force and are being ferried from the manufacturer to a belligerent for this purpose, may be attacked.
8.59 Civil aircraft on the ground may only be attacked in accordance with the normal rules relating to military objectives. However, since they may be used for transporting troops or supplies, their status will frequently depend upon the prevailing military situation. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, §§ 8.56–8.57 and 8.59.
The LOAC Manual (2006) replaces both the Defence Force Manual (1994) and the Commanders’ Guide (1994).