The KC-10 Extender airframe is based on a modified Boeing DC-10 (more precisely the "DC-10-30CF" model) and retains some 88 percent commonality of parts. Modifications are exclusive to the United States Air Force need and include revised military-grade avionics, satellite-based communications facilities, and an aerial refueling operator's station. The original DC-10 was a three-engine, widebody, jet-powered airliner entered civilian service in 1971 (with American Airlines). It featured seating for up to 380 passengers and was rated for medium- and long-distance air travel, replacing the DC-8 in the McDonnell Douglas marketing line. Production of all DC-10s officially ended in 1989 with 386 examples completed. While no longer being manufactured, the DC-10 is still in service worldwide with operators such as FedEX Express, KLM and World Airways. The USAF received a total of 60 KC-10 Extender examples from McDonnell Douglas of which 59 are still on active status. Deliveries of KC-10s spanned from 1981 to 1988 to which production lasted from 1979 to 1987. The Royal Netherlands Air Force is the only other military operator of the KC-10 Extender (known under the designation of KDC-10). While the KC-10 Extender is similar in scope to the competing Boeing KC-135 "Stratotanker", the KC-10 is a much larger airframe, carries more internal fuel and is of a more modern design (1981 versus 1957 respectively).
Refueling of other aircraft by the KC-10 Extender is accomplished either by way of an aerial refueling "hose and drogue" arrangement or by a conventional aerial refueling boom. The hose and drogue method supplies connected aircraft with a fuel transfer rate of approximately 470 gallons per minute while the boom refueling operation delivers some 1,100 gallons per minute. Lights are available for night time operations. The boom operation process is controlled by a dedicated seated boom operator viewing the situation through a wide-area window. This operator guides the boom through a digitally-based fly-by-wire control system. The refueling process is overseen by the Automatic Load Alleviation System (ALAS) as well as an Independent Disconnect System (ODS) feature to increase safety standards during the critical operation. The KC-10 retains the three base internal fuel tanks of the original DC-10 model but adds a further three large holding tanks under the cargo deck floor - one held forward, one near the wing assemblies and the other at aft. A KC-10 Extender can deliver fuel to another KC-10 or itself receive fuel from a Boeing KC-135 Stratotanker if need be. The inherent flexibility of the KC-10 ensures that it can refuel just about any military aircraft in the US or NATO inventory - particularly outside of an active military theater, helping ferrying aircraft reach their bases in preparation for action.
Origins of the KC-10 lay in the lessons learned from the air war in Vietnam and during support of the Yom Kippur War in Israel. In 1975, the US Department of Defense was convinced of a new requirement for a more capable aerial refueling tanker alongside the KC-135 and enacted the "Advanced Tanker Cargo Aircraft" program. Competing designs included converted models of the Lockheed C-5 Galaxy heavy transport, the Boeing 747 passenger airliner, the Lockheed L-1011 TriStar passenger airliner and the McDonnell Douglas DC-10 transport/passenger airliner. The final decision in December 1977 saw the DC-10 beat out the Boeing 747. First flight of the KC-10 conversion model occurred on July 12th, 1980.
The KC-10A model entered service in March of 1981 with USAF Strategic Air Command (SAC). The final twenty KC-10 airframes were then upgraded with wing-mounted fuel pods for extended refueling capabilities. A $216 million contract to Boeing was delivered to address updated avionics, navigation and communications suites to keep up with changing military and civilian airspace requirements. After their service in SAC ended come 1992, the KC-10 was assigned to the new elements of the Air Mobility Command. This included the 305th Air Mobility Wing out of Joint Base McGuire-Dix-Lakehurst, New Jersey as well as to the 60th Air Mobility Wing of Travis AFB out of California. The US Air Force Reserve Associate units (Air Force Reserve Command) also make use of the KC-10 with the 514th Air Mobility Wing at Joint Base McGuire and the 349th Air Mobility Wing at Travis AFB. The Netherlands 334th Squadron of Eindhoven Airport operates at least two KDC-10s as of this writing.
On August 1st, 1997, a merger with Boeing Company was officially completed, making McDonnell Douglas a subsidiary of the aircraft giant and former competitor. McDonnell Douglas itself was a merger of the McDonnell Aircraft and Douglas Aircraft firms on April 28th, 1967.
In addition to its refueling capabilities, the KC-10 Extender has been designed to undertake various other battlefield roles to include cargo transport, support personnel transport and MedEvac patients and litters when required. Up to 75 personnel can be carried aloft and nearly 170,000lbs of cargo can be relocated. This means that, while the KC-10 can be called on to refuel allied aircraft on a given mission, it can also transport personnel, equipment and supplies in the same sortie making her a truly multi-faceted platform - this ability no doubt "extending" the reach of the United States Air Force. Cargo is handled via a loading door and integrated winches and powered rollers facilitate movement of heavy loads within the cargo deck area. Cargo can be switched out in favor of seating for personnel or a mixed assortment of both can be included.
The design of the KC-10 is not unlike the original DC-10. The fuselage is decidedly cylindrical in nature with the cockpit held well-forward in the layout. Six framed windows provide the flight crew with adequate forward and side visibility during taxiing and flight. Rectangular access doors are set along the fuselage side. The wings are low-mounted and swept along both edges. The empennage is conventional and sports a single vertical tail fin as well as applicable horizontal tail surfaces, the latter with noticeable dihedral. The undercarriage consists of an interesting arrangement of a trio of main landing legs and a nose landing gear leg. The two outboard legs showcase four total wheels while the centerline leg fields just two wheels. Similarly, the nose landing gear leg is fitted with two wheels. The KC-10 is crewed by a standard arrangement of four base personnel made up of two pilots, a dedicated flight engineer and the boom operator. Various sorties can dictate the need for additional specialists or crew as needed. The base MedEvac crew typically consists of three medical technicians and two flight nurses.
In keeping with the engine layout of the DC-10, the KC-10 is powered by three General Electric CF6-50C2 turbofan engines arranged in single engine nacelles (one under each wing) and the third near the base of the vertical tail fin. These engines supply the airframe with up to 52,500lbs of thrust each and allow for speeds near 619 miles per hour with a ceiling of 42,000 feet/ Maximum take-off weight is rated at 590,000lbs and overall range - sans any cargo - is in the vicinity of 11,500 miles. Maximum fuel load from all six internal fuel stores is 356,000lbs - noted as twice the available fuel carried by the smaller Boeing KC-135 Stratotanker series.
The KC-10 Extender was utilized in the 1986 air strikes against Libya. When USAF General Dynamics F-11 Aardvark strike fighters operating from the UK were denied overflights across Europe, the KC-10 ensured that these twenty-nine Aardvarks could reach the target areas and hit their marks.
The KC-10 Extender was later called to action in support of Gulf War during operations Desert Shield and Desert Storm. Its versatility allowed aircrews to refuel the coalition-based air force that was made up of various aircraft types spanning decades and was responsible for relocating thousands of troops and tons of cargo pallets to the Persian Gulf region during the initial build-up phase. During the whole of the war, KC-10 crews maintained a spotless record of on-time fuel deliveries to awaiting aircraft and help extend flight times for strike, interception and bombing sorties.
The KC-10 Extender also partook of actions during the upcoming engagement of the Bosnia-Kosovo War as part of Operation Allied Force. KC-10s arrived in the theater as part of the NATO force by May of 1999 and were put to work in refueling the various American and European-based airframes. In all, the KC-10 recorded 409 sorties in the air campaign which eventually saw a major restructuring of the nation of Yugoslavia.
The KC-10 Extender family has continued to see extensive and ongoing actions since the 2001 American invasion of Afghanistan following the events of 9/11 and in the 2003 American invasion of Iraq to overthrow the Iraqi government and unseat leader Saddam Hussein. To that end, the KC-10 is sure to provide several more years of faithful service to the United States Air Force and NATO. Boeing estimates its KC-10 to last past 2015.