The Army project manager Col. William H. Forster published a list of 101 action items. In 1986, the four 22-foot-long main rotor blades, each made from steel and composite material glued together to maximize strength and minimize weight by the Composite Structures Division of Alcoa Composites, were added to the list. The steel-composite rotors could not meet the Army specification for a life of 1500 flight hours, and needed replacment after just 146 hours. After six changes to the design, the rotor blade life was extended to 1400 hours by early 1991. Further development During the 1980s, McDonnell Douglas studied an AH-64B, featuring an updated cockpit, new fire control system and other upgrades. In 1988, funding was approved for a multi-stage upgrade program to improve sensor and weapon systems. Technological advance led to the program's cancellation in favor of more ambitious changes. In August 1990, development of the AH-64D Apache Longbow was approved by the Defense Acquisition Board. The first AH-64D prototype flew on 15 April 1992. Prototype testing ended in April 1995. During testing, six AH-64D helicopters were pitted against a bigger group of AH-64As. The results demonstrated the AH-64D to have a sevenfold increase in survivability and fourfold increase in lethality compared to the AH-64A. On 13 October 1995, full-scale production was approved; a $1.9-billion five-year contract was signed in August 1996 to upgrade 232 AH-64As into AH-64Ds. On 17 March 1997, the first production AH-64D flew. It was delivered on 31 March. Portions of the Apache are produced by other aerospace firms. AgustaWestland has produced number of components for the Apache, both for the international market and for the British Army's AgustaWestland Apache. Since 2004, Korea Aerospace Industries has been the sole manufacturer of the Apache's fuselage. Fuselage production had previously been performed by Teledyne Ryan Aeronautical. The transfer of fuselage production led to a prolonged legal dispute between Teledyne Ryan and Boeing. The AH-64D program cost a total of $11 billion through 2007. In April 2006, Boeing was awarded a $67.6 million fixed-price contract for the remanufacture of several existing U.S. AH-64As to the AH-64D configuration. Between May 2009 and July 2011, a further five contracts were issued to remanufacture batches of AH-64As into AH-64Ds. Since 2008, nations operating the older Apaches have been urged to undertake modernization programs as support for the AH-64A is withdrawn. By May 2019, Boeing tested in a wind tunnel a