Click on Picture to enlarge


The KC-135 "Stratotanker"

+ Larger Font | - Smaller Font


The Mission

The KC-135 Stratotanker's principal mission is air refueling. This unique asset greatly enhances the USAF's capability to accomplish its primary missions of Global Reach and Global Power. It also provides aerial refueling support to Air Force, Navy and Marine Corps aircraft as well as aircraft of allied nations.



Four turbofans, mounted under 35-degree swept wings, power the KC-135 to takeoffs at gross weights up to 322,500 pounds (146,285 kilograms). Nearly all internal fuel can be pumped through the tanker's flying boom, the KC-135 's primary fuel transfer method. A special shuttlecock-shaped drogue, attached to and trailing behind the flying boom, may be used to refuel aircraft fitted with probes. An operator stationed in the rear of the plane controls the boom. A cargo deck above the refueling system can hold a mixed load of passengers and cargo. Depending on fuel storage configuration, the KC-135 can carry up to 83,000 pounds (37,648 kilograms) of cargo.

In Southeast Asia, KC-135 Stratotankers made the air war different from all previous aerial conflicts. Midair refueling brought far-flung bombing targets within reach. Combat aircraft, no longer limited by fuel supplies, were able to spend more time in target areas.




AMC manages more than 530 total aircraft inventory Stratotankers, of which the Air Force Reserve and Air National Guard fly 295 of those in support of AMC's mission.

The Boeing Company's model 367-80 was the basic design for the commercial 707 passenger plane as well as the KC-135A Stratotanker. In 1954 the Air Force purchased the first 29 of its future 732-plane fleet. The first aircraft flew in August 1956 and the initial production Stratotanker was delivered to Castle Air Force Base, Calif., in June 1957. The last KC-135 was delivered to the Air Force in 1965.

Of the original KC-135A's, more than 410 have been modified with new CFM-56 engines produced by CFM-International. The re-engined tanker, designated either the KC-135R or KC-135T, can offload 50 percent more fuel, is 25 percent more fuel efficient, costs 25 percent less to operate and is 96 percent quieter than the KC-135A.

Under another modification program, 157 Air Force Reserve and Air National Guard tankers were re-engined with the TF-33-PW-102 engines. The re-engined tanker, designated the KC-135E, is 14 percent more fuel efficient than the KC-135A and can offload 20 percent more fuel.

Through the years, the KC-135 has been altered to do other jobs ranging from flying command post missions to reconnaissance. RC-135s are used for special reconnaissance and Air Force Material Command's NKC-135A's are flown in test programs. The Air Combat Command operates the OC-135 as an observation platform in compliance with the Open Skies Treaty.

Over the next few years, the aircraft will undergo upgrades to expand its capabilities and improve its reliability. Among these are improved communications, navigation and surveillance equipment to meet future civil air traffic control needs.


General Characteristics

Primary Function: Aerial refueling and airlift
Prime Contractor: The Boeing Company
Power Plant: KC-135R/T, CFM International CFM-56 turbofan engines; KC-135E, Pratt and Whitney TF-33-PW-102 turbofan engines
Thrust: KC-135R, 21,634 pounds each engine; KC-135E, 18,000 pounds each engine
Wingspan: 130 feet, 10 inches (39.88 meters)
Length: 136 feet, 3 inches (41.53 meters)
Height: 41 feet, 8 inches (12.7 meters)
Speed: 530 miles per hour at 30,000 feet (9,144 meters)
Ceiling: 50,000 feet (15,240 meters)
Range: 1,500 miles (2,419 kilometers) with 150,000 pounds (68,039 kilograms) of transfer fuel; ferry mission, up to 11,015 miles (17,766 kilometers)
Maximum Takeoff Weight: 322,500 pounds (146,285 kilograms)
Maximum Transfer Fuel Load: 200,000 pounds (90,719 kilograms)
Maximum Cargo Capability: 83,000 pounds (37,648 kilograms), 37 passengers
Pallet Positions: 6
Crew: Four: pilot, co-pilot, navigator, boom operator. Aircraft equipped with PACER CRAG do not have a navigator on most missions. The Air Force procured a limited number of navigator suites that can be installed for unique missions.
Unit Cost: $39.6 million (FY98 constant dollars)
Date Deployed: August 1956
Inventory: Active duty, 235; Air National Guard, 220; Air Force Reserve, 75


CFM Engine Replacement

To increase takeoff and carrying capacity, improve fuel efficiency, and reduce engine noise and pollution levels, Boeing replaced the original KC-135A engines with CFM56 engines for the U.S. Air Force. The serviced aircraft were re-designated as KC-135Rs, and the engine-replacement program achieved the following results:


JT3D Engine Replacement

The Air Force Reserve and Air National Guard retained Boeing to replace KC-135-A engines with refurbished JT3D engines taken from used commercial 707 airliners. The aircraft designation changed to KC-135E, and the program achieved the following results:

  • Increased engine power 30%

  • Reduced noise levels 85%

  • Replaced/refurbished struts and cowling, brakes, cockpit controls, and instruments



The KC-135R


Click on Picture to enlarge

The KC-135 Stratotanker's primary mission is to refuel long-range bombers. It also provides aerial refueling support to Air Force, Navy, Marine Corps and allied aircraft.

Four turbojets, mounted under wings swept 35 degrees, power the KC-135. Nearly all internal fuel can be pumped through the tanker's flying boom, the KC-135's primary fuel transfer method. A special shuttlecock-shaped drogue, attached to and trailed behind the flying boom, is used to refuel aircraft fitted with probes. An operator stationed in the rear of the plane controls the boom. A cargo deck above the refueling system holds passengers or cargo. Depending on fuel storage configuration, the KC-135 can carry up to 83,000 pounds (37,350 kilograms) of cargo.

The KC-135 tanker fleet made an invaluable contribution to the success of Operation Desert Storm in the Persian Gulf, flying around-the-clock missions to maintain operability of allied warplanes. The KC-135s form the backbone of the Air Force tanker fleet, meeting the aerial refueling requirements of bomber, fighter, cargo and reconnaissance forces, as well as the needs of the Navy, Marines and allied nations.



Because the KC-135A's original engines are of 1950s technology, they don't meet modern standards of increased fuel efficiency, reduced pollution and reduced noise levels. By installing new, CFM56 engines, performance is enhanced and fuel off-load capability is dramatically improved. In fact, the modification is so successful that two-re-engined KC-135Rs can do the work of three KC-135As.

This improvement is a result of the KC-135R's lower fuel consumption and increased performance which allow the tanker to take off with more fuel and carry it farther. Since the airplane can carry more fuel and burn less of it during a mission, it's possible to transfer a much greater amount to receiver aircraft.

The quieter, more fuel-efficient CFM56 engines are manufactured by CFM International, a company jointly owned by SNECMA of France, and General Electric of the U.S. The engine is an advanced-technology, high- bypass turbofan; the military designation is F108-CF-100. Related system improvements are incorporated to improve the modified airplane's ability to carry out its mission, while decreasing overall maintenance and operation costs. The modified airplane is designated a KC-135R.

Because the KC-135R uses as much as 27 percent less fuel than the KC-135A, the USAF can expect huge fuel savings by re-engining its fleet of KC-135s - about $1.7 billion over 15 years of operation. That's enough to fill the gas tanks of some 7.7 million American cars each year for a decade and a half. Annual savings are estimated to be about 2.3 to 3.2 million barrels of fuel, about three to four percent of the USAF's annual fuel use. This equals the fuel needed to provide electrical power for 145 days to a city of 350,000 to 400,000.

Re-engine with the CFM56 engines also results in significant noise reductions. Area surrounding airports exposed to decibel noise levels is reduced from over 240 square miles to about three square miles. This results in a reduction in the noise impacted area of more than 98 percent. Maximum take-off decibel levels drop from 126 to 99 decibels. This meets the tough U.S. Federal Air Regulation standards -- a goal for commercial aircraft operated within the U.S. In addition, smoke and other emission pollutants are reduced dramatically.

Boeing has delivered approximately 400 re-engined KC-135Rs and is under contract for about 432 re-engine kits. Each kit includes struts, nacelles, 12.2 miles of wiring, and other system modification components. Engines are purchased directly by the Air Force from CFM International.

Boeing has completed work on a program to re-engine all KC-135As in the Air Force Reserve and Air National Guard fleet -- a total of 161 airplanes. In that modification program, which began in 1981, KC-135As were modified with refurbished JT3D engines taken from used, commercial 707 airliners. After modification, the airplanes are designated KC-135Es. This upgrade, like the KC-135R program, boosts performance while decreasing noise and smoke pollution levels. The modified KC-135E provides 30 percent more powerful engines with a noise reduction of 85 percent.

The program included acquisition of used 707s, procurement of purchased parts and equipment, basic engineering, some parts manufacturing, and refurbishment and installation of the engines, struts and cowling. Kits also included improved brakes, cockpit controls and instruments.

The Multi-Point Refueling System Program is an effort to enhance the efficiency and flexibility of the Air Forceís air refueling fleet, 45 KC-135R Stratotanker aircraft are being outfitted to accept wing-tip, hose-and-drogue and air refueling pods for refueling NATO and US Navy aircraft. US Navy and many NATO aircraft cannot be refueled using the boom and receptacle refueling method of Air Force aircraft, and instead use a probe-and-drogue system where probes on the receiver aircraft make contact with a hose that is reeled out behind a tanker aircraft. With the number of worldwide joint and combined military operations on the rise, the Department of Defense directed the Air Force to outfit part of its KC-135 fleet with the capability of refueling both probe-and-drogue and boom receptacle aircraft on the same mission. This also allows refueling up to two probe-and-drogue aircraft at the same time. Managed by the KC-135 Development System Office at Aeronautical Systems Center, Wright-Patterson Air Force Base, Ohio, hte program completed the engineering, manufacturing and development portion of the program in 1998 year and began follow-on operational test and evaluation early in 1999.

With projected modifications, the KC-135 will fly and refuel into the next century. A new aluminum-alloy skin grafted to the underside of the wings will add 27,000 flying hours to the aircraft. Aircraft corrosion presents a significant challenge to AMC. It is presently difficult if not impossible to model this major life limiting factor over long periods of time. Technologies required to deal with corrosion have not evolved, leaving AMC with a deficiency that of not knowing exactly how long its older aircraft will operate economically. At current use rates, the KC-135 aircraft structure should remain sound. The fleet is projected to be in the Air Force service well into the next century. In fact, calculations using a predicted structural service life of 70,000 hours (structural data only) and based on current annual flight hours reveal that the structural life could extend into the twenty-second century. However, these numbers taken alone are misleading as they do not include the effects of corrosion.

Most experts agree that the R-model and T-model will continue to operate economically well into the next century. The R-models maintenance capability and reliability rates are among the highest of any weapon system AMC operates, and its operating cost is the lowest. The E-model economic service life is markedly different because of the difference in age and technology of some of its major components, most notably the engines. The basic airframe should, in theory, last as long as the R-model, but the age of the engines points to the likelihood that upkeep could become expensive (in terms of parts and maintenance man-hours). The TF-33 (E-model) engines were previously used but refurbished to an expected 6,000 hour service life. At current use rates, the TF-33 will need another major overhaul around the turn of the century. Additionally, since the TF-33 does not meet FAA Stage III noise requirements for the year 2000, more time and money must be expended to ensure compliance.

The U.S. Air Force has also acknowledged that the cockpit of the KC-135 must be modernized. The Air Force issued a solicitation for PACER CRAG in May 1995. This upgrade will provide new compass and radar and add global positioning system in the KC-135 cockpit. PSD has submitted a proposal to be the prime contractor for this activity which includes engineering, and manufacturing development, prototype installation, test and evaluation, and kit production. Contract award was expected in October 1995.

Additional cockpit improvements beyond the PACER CRAG program, would maximize crew efficiency and reduce operation and maintenance costs. With extensive experience in avionics integration, Boeing could offer a new cockpit for the KC-135 that would increase avionics reliability, while allowing the potential for reducing the number of crew members. The newer cockpit would be part of an avionics modernization for the airplane.

The existing cockpit consists of electro-mechanical equipment of 1950s technology with individual control panels and instrumentation distributed throughout. Failure rates are high and repair capability has been restricted significantly as technology has changed. Not only are repairs to the KC-135's existing avionics suite costly for the Air Force, but they also mean more down-time for the tanker while repairs are made. Modem commercial airplane avionics are much more reliable than those aboard the KC-135.

Boeing believes that an avionics modernization program is essential to assure the KC-135 has the technology to perform its mission well in the years ahead. An integrated avionics system would be easier to operate and maintain. The new digital cockpit would include an upgraded multiplex data bus and integration software, integrating global positioning, ground collision avoidance, mission management and inertial navigation systems. Controls would include multi functional electronic displays and centralized control panels.


Primary Function: Aerial refueling
Contractor: Boeing Military Airplanes
Power Plant: Four CFM-International F108-CF-100 turbofans
Thrust: 22,224 pounds (10,000.8 kilograms) each engine
Length: 136 feet, 3 inches (40.8 meters)
Height: 38 feet, 4 inches (11.5 meters)
Wingspan: 130 feet, 10 inches (39.2 meters)
Speed: Maximum speed at 30,000 feet (9,100 meters) 610 mph (Mach 0.93)
Ceiling: 50,000 feet (15,152 meters)
Weight: 119,231 pounds (53,654 kilograms) empty
Maximum Takeoff Weight: 322,500 pounds (145,125 kilograms)
Range: 11,192 miles (9,732 nautical miles) with 120,000 pounds (54,000 kilograms) of transfer fuel.
Crew: Four or five; up to 80 passengers.
Date Deployed: August 1965.
Unit Cost: KC-135R, $53 million; KC-135E, $30.6 million; KC-135A, $26.1 million.
Inventory: Active force, 457; Reserve, 30; ANG, 158.


Click on Picture to enlarge



KC-135 Stratotanker Air-To-Air Refueling


Click on Picture to enlarge

The Boeing company built 732 KC-135 Stratotankers for the US Air Force between 1957 and 1965. The US Air Force still has about 550 KC-135 Stratotankers in service (active duty, 253; Air National Guard, 222; Air Force Reserve, 70) and has made substantial investment in a series of upgrade programs, including reskinning of the lower wing surfaces, the installation of new CFM56 engines and new avionics systems. 411 of the aircraft in service are the upgraded 135R models and 134 the older 135E. The KC-135 is also in service with the air forces of France (11 aircraft), Turkey (seven) and Singapore (four).




The primary air fuel transfer method is through the tanker's flying boom, controlled by an operator stationed at the rear of the fuselage. USAF aircraft have primarily used this boom and receptacle refueling technique.

A shuttlecock drogue can be trailed behind the boom and used to refuel aircraft equipped with refueling probes. Aircraft fitted with the boom drogue cannot refuel boom and receptacle aircraft.


Hose & Drogue Air Refueling

About 45 US Air Force KC-135R Stratotankers are fitted with Mark 32B wingtip hose and drogue air refueling pods, which are supplied by Flight Refueling Ltd. These are capable of refueling Navy and NATO aircraft, which use a probe and drogue system instead of a boom and receptacle. The receiving aircraft approaches the tanker and its probe makes contact with a hose reeled out and trailing from the tanker. The additional system allows the KC-135R to refuel both probe/drogue and boom/receptacle aircraft on a single mission and to refuel two probe/drogue aircraft simultaneously.

The installation of wingtip refueling pods involves a major modification and refit to the entire aircraft, including modifications to the wing and fuselage fuel tanks, additional fuel control systems and the installation of indicators and circuit breakers on the flight deck.

Inside the refueling pods, a collapsible funnel-shaped drogue is attached to a hose, which is reeled out to trail behind the wing of the aircraft. The hose is fitted with a constant tension spring to give stability to the hose while it is extended.



Passengers and up to 37,650kg cargo can be carried on the cargo deck above the refueling systems.



The USAF selected Rockwell Collins to carry out the modernization of the avionics system under the KC-135 Pacer CRAG (Compass, Radar and Global Positioning System) program. The upgraded avionics include cockpit enhancements with the Collins FMS-800 integrated flight management system, Collins FDS-255 liquid crystal flat-panel multifunction flight display, and the Collins WXR-700X forward-looking predictive wind-shear weather radar. The flight management system is integrated with a traffic alert and collision avoidance system (TCAS) and an enhanced ground proximity warning system (EGPWS).

Subsequent to the Pacer CRAG program, the USAF selected Rockwell Collins to update the KC-135 flight deck in support of the Global Air Traffic Management (GATM) initiative. The GATM upgrade program will focus primarily on upgrading the aircraft's communication and navigation systems to free operation in civil airspace. 50 of the 550 USAF aircraft are to receive the upgrade under the Phase I low-rate initial production contract and the first production aircraft was delivered in August 2003. The second LRIP contract, signed in July 2003, provided for a further 25 aircraft to be upgraded. The Phase II full rate production contract for 30 more systems was signed in April 2004. 100 upgraded aircraft have been delivered.

GATM additions to the communications system include an Aero-I SAT-2000 satellite communications system and two FANS (future air navigation) capable CMU-900 Communication Management Units for data link applications. Also, the addition of two Collins Integrated Processing Centres provides an integrated, modularized platform for hosting several partitioned GATM-related software applications.

GATM additions to the navigation system include two Collins GNLU-955M Multi-Mode Receivers, which contain individual modules for GPS, MLS and FM-Immune VOR/ILS (VHF omni-directional radio range steering guidance linked with an instrument landing system) capabilities. Additionally, one existing and one newly added Embedded Global Positioning System/Inertial Navigation System (EGI) unit will possess twelve-channel, all-in-view GPS receivers.


Mission Variants

Some KC-135 aircraft have been configured for other missions such as reconnaissance and as a flying command post. The US Air Combat Command operates 14 RC-135V/W Rivet Joint reconnaissance aircraft and the OC-135B Open Skies observation aircraft and the US Strategic Command operates the EC-135 Flying Command Post. The US Strategic Command has one EC-135C on alert status at all times, ready to take command if ground control is compromised.



The KC-135R aircraft has been updated with more efficient CFM International CFM-56 engines, which burn up to 25% less fuel and provide greater thrust than previously fitted engines. The efficiency of the engines enable the aircraft to offload 50% more fuel on a medium-radius, 1,725-mile refueling mission. 410 of the USAF fleet of 546 KC-135ís have been re-engined. The remainder have Pratt & Whitney TF33-102 engines.



KC-135  Photo Gallery


Click on Picture to enlarge





Last Updated