BOEING 720

Produced in two models, the 720 and the 720B, this intermediate-range Boeing transport looks very much like the Boeing 707. The first model, the 720, uses four Pratt & Whitney JT3D-7 turbojet engines rated at 12,500 pounds of thrust each. The 720B is powered by JT3D-3 turbofan engines with a thrust rating of 18,000 pounds each. The difference in thrust allows the 720B to carry almost 15,000 pounds more payload than the 720. One way to tell the difference between the 720 and its big brother the 707 is to count the overwing emergency-exit doors. The 707 has two doors over each wing, but the 720's smaller passenger capacity allows for only one over-wing door on each side. Another way to distinguish the two jetliners is to look at the engine housings. A large hump on top of the engine indicates the presence of a turbocompressor, or "TC," used for cabin pressurization and air conditioning. The 720 is equipped with two TCs; the 707 has three.