Related Rule
Practice Relating to Rule 48. Attacks against Persons Parachuting from an Aircraft in Distress
Switzerland’s Basic Military Manual (1987) states:
If the occupants of an aircraft in distress bale out by parachute to save their lives, it is not legitimate to attack them from the ground or from an aircraft during their descent. As soon as those persons reach the ground, they may be captured. If they resist or show hostile intent, they may be placed hors de combat.
Paratroopers may be placed hors de combat even before they reach the ground, whether they parachute alone or in massive groups. 
Switzerland, Lois et coutumes de la guerre (Extrait et commentaire), Règlement 51.7/II f, Armée Suisse, 1987, Articles 49 and 50.
Switzerland’s Regulation on Legal Bases for Conduct during an Engagement (2005) states:
183 As long as they do not defend themselves, pilots and crew members who parachute from an enemy aircraft in distress to save their own lives may neither be attacked from the air nor from the ground. Once landed, they are treated as prisoners of war. If they do not surrender or resist capture they are considered combatants and may be rendered hors de combat. 
Switzerland, Bases légales du comportement à l’engagement (BCE), Règlement 51.007/IVf, Swiss Army, issued based on Article 10 of the Ordinance on the Organization of the Federal Department for Defence, Civil Protection and Sports of 7 March 2003, entry into force on 1 July 2005, § 183; see also § 172.