Figure 1-1.  Search and rescue helicopter conducting a pinnacle  approach.  1-2 Figure 1-2.  Search and rescue helicopter landing in a confined area.  Turbine Age As an aircraft, the primary advantages of the helicopter are  due to the rotor blades that revolve through the air, providing  lift without requiring the aircraft to move forward. This lift  allows the helicopter to hover in one area and to take off  and land vertically without the need for runways. For this  reason, helicopters are often used in congested or isolated  areas where fixed-wing aircraft are not able to take off or  land. [Figures 1-1  and  1-2] Piloting a helicopter requires adequate, focused and safety- orientated training. It also requires continuous attention  to the machine and the operating environment. The pilot  must work in three dimensions and use both arms and  both legs constantly to keep the helicopter in a desired  state. Coordination, timing and control touch are all used  simultaneously when flying a helicopter. Although helicopters were developed and built during the  first half-century of flight, some even reaching limited  production; it was not until 1942 that a helicopter designed by  Igor Sikorsky reached full-scale production, with 131 aircraft  built. Even though most previous designs used more than one  main rotor, it was the single main rotor with an antitorque  tail rotor configuration that would come to be recognized  worldwide as the helicopter. In 1951, at the urging of his contacts at the Department of  the Navy, Charles H. Kaman modified his K-225 helicopter  with a new kind of engine, the turbo-shaft engine. This  adaptation of the turbine engine provided a large amount of  horsepower to the helicopter with a lower weight penalty  than piston engines, heavy engine blocks, and auxiliary  components. On December 11, 1951, the K-225 became  the first turbine-powered helicopter in the world. Two years  later, on March 26, 1954, a modified Navy HTK-1, another  Kaman helicopter, became the first twin-turbine helicopter  to fly. However, it was the Sud Aviation Alouette II that  would become the first helicopter to be produced with a  turbine engine.  Reliable helicopters capable of stable hover flight were  developed decades after fixed-wing aircraft. This is largely  due to higher engine power density requirements than  fixed-wing aircraft. Improvements in fuels and engines  during the first half of the 20$^{th}$ century were critical factors  in helicopter development. The availability of lightweight  turbo-shaft engines in the second half of the 20$^{th}$ century led  to the development of larger, faster, and higher-performance  helicopters. While smaller and less expensive helicopters  still use piston engines, turboshaft engines are the preferred  powerplant for helicopters today. The turbine engine has the following advantages over a  reciprocating engine: •  Less vibration •  Increased aircraft performance • Reliability •  Ease of operation 