compound Apache scale model with a pusher propeller, a small wing to increase range and speed, and a counter-torque tail rotor like the cancelled Lockheed AH-56 Cheyenne of the 1960s. It competed for the U.S. Army's FLRAA unveiled in April, developed from the Future Vertical Lift Capability Set 3 (medium rotorcraft) without the attack requirement, while the U.S. Army's FARA should replace the retired Bell OH-58 Kiowa scout and up to half of the AH-64 fleet. Design Overview The AH-64 Apache has a four-blade main rotor and a four-blade tail rotor. The crew sits in tandem, with the pilot sitting behind and above the co-pilot/gunner. Both crew members are capable of flying the aircraft and performing methods of weapon engagements independently. The AH-64 is powered by two General Electric T700 turboshaft engines with high-mounted exhausts on either side of the fuselage. Various models of engines have been used on the Apache; those in British service use engines from Rolls-Royce. In 2004, General Electric Aviation began producing more powerful T700-GE-701D engines, rated at for AH-64Ds. The crew compartment and rotor blades are designed to sustain a hit from rounds. The airframe includes some of protection and has a self-sealing fuel system to protect against ballistic projectiles. This compartment also incorporates a transparent blast shield between the pilot and gunner seats so that at least one crew member can survive in the event of a direct hit, but the canopy and windows are otherwise unrated against ballistic threats. The aircraft was designed to meet the crashworthiness requirements of MIL-STD-1290, which specifies minimum requirement for crash impact energy attenuation to minimize crew injuries and fatalities. This was achieved through incorporation of increased structural strength, crashworthy landing gear, seats and fuel system. On a standard day, when temperatures are 59 °F (15 °C), the AH-64 has a vertical rate of climb of 1,775 feet per minute (541 m/min), and a service ceiling of 21,000 feet (6,400 m). However, on a hot day, when temperatures are 70 °F (21 °C), its vertical rate of climb is reduced to 1,595 fpm (486 m/min), and service ceiling is reduced to 19,400 feet (5,900 m) due to less dense air. Avionics and targeting One of the revolutionary features of the Apache was its helmet mounted display, the Integrated Helmet and Display Sighting System (IHADSS); among its capabilities, either the pilot or gunner can slave the helicopter's 30 mm