It is mandatory for United Nations system personnel and eligible family members to obtain security clearance for all official travel, regardless of location, and they cannot commence official travel without obtaining it except in compelling cases, where insufficient time is available such as during periods requiring immediate medical evacuation or other life-threatening situation. For the purpose of this policy, official travel includes official home leave or other entitlement travel where the cost of travel is borne by organizations of the United Nations system. This applies regardless of whether official travel is undertaken by air, sea, land, or any combination thereof.