Air freight transport chains may be formed in different ways. Terminal to terminal transport of goods may be carried out by co-loading them onto a passenger plane (Lower Deck) or using a cargo plane. Besides all-cargo planes such as the Boeing 747 or the Mc Donald Douglas MD 11F, there are the so-called mixed versions or quick changes, which can be used flexibly as either passenger or cargo planes. In most cases, pre-carriage from the sender to the airport and on-carriage from the airport to the receiver are carried out by truck. In many cases, main carriage is also performed as ground transport on behalf of the airline. This is referred to as Road Feeder Service (RFS) or trucking. In these cases, the freight retains its status as air freight and is billed accordingly.