Related Rule
Practice Relating to Rule 7. The Principle of Distinction between Civilian Objects and Military Objectives
Section E. Attacks against civilian means of transportation
Germany’s Military Manual (1992) provides that enemy aircraft used exclusively for the transport of civilians may neither be attacked nor seized. Their protection ends
if such [aircraft] do not comply with conditions lawfully imposed upon them, if they abuse their mission or are engaged in any other activity bringing them under the definition of a military objective … Such aircraft may be requested to land on ground or water to be searched. 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten Konflikten – Handbuch, August 1992, §§ 1034–1036; see also § 463.