The United States of America is recruiting civil aircraft from several airlines to evacuate people from Kabul. At the moment, however, it is not planned that these should fly to Afghanistan, but only carry out onward transport, for example from Ramstein.
According to an official announcement, Omni Air, Delta Air Lines and American Airlines are currently in use with three planes each. Hawaiian Airlines helps out with two aircraft and United Airlines even with four of them. The legal basis is that Secretary of Defense Llyod Austin activated the first stage of what is known as the Civil Reserve Air Fleet.
Specifically, this means that the Ministry of Defense can requisition civil aircraft in the event of war or crisis. This has happened several times in the past. The aircraft is used for the transport of people or goods. There is a precise step-by-step plan that stipulates how many planes can be drawn in.
These are then under the command of the military, but do not fly under the military rules, but continue to fly under those for civil air traffic. After completing the mission, the machines and their crews will be returned. The airlines concerned receive compensation, which is also stipulated by law, for their work.