Most jetliners are equipped with PACKs, which stands for Pressurization Air Conditioning Kit. The location of the air conditioning (AC) PACK(s) depends on the design of the aircraft. In some designs, they are installed in the wing-to-body fairing between the two wings beneath the fuselage. On other aircraft (Douglas Aircraft DC-9 Series) the AC PACKs are located in the tail. The aircraft PACKs on the McDonnell Douglas DC-10/MD-11 and Lockheed L-1011 are located in the front of the aircraft beneath the flight deck. Nearly all jetliners have two PACKs, although larger aircraft such as the Boeing 747, Lockheed L-1011, and McDonnell-Douglas DC-10/MD-11 have three.