Boeing KC-135 Stratotanker

The Boeing KC-135 Stratotanker is a military aerial refueling aircraft. It and the Boeing 707 airliner were developed from the Boeing 367-80 prototype. The KC-135 was the US Air Force's first jet-powered refueling tanker and replaced the KC-97 Stratotanker. The Stratotanker was initially tasked to refuel strategic bombers, but was used extensively in the Vietnam War and later conflicts such as Operation Desert Storm to extend the range and endurance of US tactical fighters and bombers.

The KC-135 entered service with the United States Air Force (USAF) in 1957; it is one of six military fixed-wing aircraft with over 50 years of continuous service with its original operator. The KC-135 is supplemented by the larger KC-10. Despite increased maintenance costs, studies conclude many of the aircraft could be flown until 2040. The aircraft will eventually be replaced by the Boeing KC-46.

Background
Like its sibling, the commercial Boeing 707 jet airliner, the KC-135 was derived from the Boeing 367-80 jet transport "proof of concept" demonstrator, which was commonly called the "Dash-80". As such the KC-135 is similar in appearance to the 707, but has a narrower fuselage and is shorter than the 707. The KC-135 predates the 707, and is structurally quite different from the civilian airliner. Boeing gave the future KC-135 tanker the initial designation Model 717.

In 1954 USAF's Strategic Air Command held a competition for a jet-powered aerial refueling tanker. Lockheed's tanker version of the proposed Lockheed L-193 airliner with tail-mounted engines was declared the winner in 1955. Since Boeing's proposal was already flying, the KC-135 could be delivered two years earlier and Air Force Secretary Harold E. Talbott ordered 250 KC-135 tankers until the Lockheed's design could be manufactured. In the end, orders for the Lockheed tanker were dropped rather than supporting two tanker designs. Lockheed never produced its jet airliner, while Boeing would eventually dominate the market with a family of airliners based on the 707.

In 1954 the Air Force placed an initial order for 29 KC-135As, the first of an eventual 820 of all variants of the basic C-135 family. The first aircraft flew in August 1956 and the initial production Stratotanker was delivered to Castle Air Force Base, California, in June 1957. The last KC-135 was delivered to the Air Force in 1965.

Developed in the early 1950s, the basic airframe is characterized by 35-degree aft swept wings and tail, four underwing-mounted engine pods, a horizontal stabilizer mounted on the fuselage near the bottom of the vertical stabilizer with positive dihedral on the two horizontal planes and a hi-frequency radio antenna which protrudes forward from the top of the vertical fin or stabilizer. These basic features make it strongly resemble the commercial Boeing 707 and 720 aircraft, although it is actually a different aircraft.

Reconnaissance and command post variants of the aircraft, including the RC-135 Rivet Joint and EC-135 Looking Glass Post Attack Command & Control Systems were operated by SAC from 1963 through 1992, when they were re-assigned to the Air Combat Command (ACC). The USAF EC-135 Looking Glass was subsequently replaced in its role by the U.S. Navy E-6 Mercury aircraft, a new build airframe based on the Boeing 707-320B.

General upgrades


The KC-135Q variant was modified to carry JP-7 fuel necessary for the SR-71 Blackbird, segregating the JP-7 from the KC-135's own fuel supply (the body tanks carrying JP-7, and the wing tanks carrying JP-4 or JP-8). When the KC-135Q model received the CFM-56 engines, it was redesignated the KC-135T model, which was capable of separating the main body tanks from the wing tanks where the KC-135 draws its engine fuel. The only external difference between a KC-135R and a KC-135T is the presence of a clear window on the underside of the empennage of the KC-135T where a remote controlled searchlight is mounted. It also has two ground refueling ports, located in each rear wheel well so ground crews can fuel both the body tanks and wing tanks separately.

Eight KC-135R aircraft are receiver-capable tankers, commonly referred to as KC-135R(RT). All eight aircraft were with the 22d Air Refueling Wing at McConnell AFB, KS as of 1994. They are primarily used for force extension and Special Operations missions, and are crewed by highly qualified receiver capable crews. If not used for the receiver mission, these aircraft can be flown just like any other KC-135R.

In order to expand the KC-135's capabilities and improve its reliability, the aircraft has undergone a number of upgrades. Among these was the Pacer-CRAG program (CRAG=Compass, Radar And GPS) which ran from 1999 to 2002 and modified all the aircraft in the inventory to eliminate the Navigator position from the flight crew. The program development was done by Rockwell Collins in Iowa and installation was performed by BAE Systems at the Mojave Airport in California. The latest block upgrade to the KC-135 is Block 40.5 which allows the KC-135 to comply with Global air-traffic management. The KC-135 Block 45 program is expected to come online in 2014 and addresses non-procurable instrument upgrades as well as a new autopilot system.

Re-engining
All KC-135s were originally equipped with Pratt & Whitney J-57-P-59W turbojet engines which produced 10000 lbf of thrust dry, and approximately 13000 lbf of thrust wet. Wet thrust is achieved through the use of water injection on takeoff. 670 USgal of water are injected into the engines over the course of two and a half minutes. This water allows a second set of fuel injectors to activate without melting the turbine buckets. The water turns to steam and is ejected out the rear of the engine, increasing the exhaust mass and increasing thrust. The engine runs somewhat hotter, with more engine noise.

In the 1980s the first modification program re-engined 157 Air Force Reserve (AFRES) and Air National Guard (ANG) tankers with the Pratt & Whitney TF-33-PW-102 engines from 707 airliners retired in the late 1970s and early 1980s. The re-engined tanker, designated the KC-135E, was 14% more fuel efficient than the KC-135A and could offload 20% more fuel on long duration flights. (The difference is that the A-model weighed only 104000 lb empty, while the E-model weighed 115000 lb empty. But the maximum takeoff weight was not increased for the E-model.  Therefore, the A-model could takeoff with 200000 lb of fuel, while the E-model could only takeoff with 190000 lb of fuel.)  Only the KC-135E aircraft were equipped with thrust-reversers for takeoff aborts and shorter landing roll-outs. The KC-135E fleet has since either been re-engined into the R-model configuration or placed into long term storage ("XJ"), as Congress has prevented the Air Force from formally retiring them. The final KC-135E, tail number 56-3630, was delivered by the 101st Air Refueling Wing of the Maine Air National Guard to the 309th Aerospace Maintenance and Regeneration Group (AMARG) at Davis-Monthan Air Force Base in September 2009.



The second modification program re-engined 500 aircraft with new CFM International CFM56 (military designation: F108) engines produced by General Electric and Snecma. The CFM-56 turbofans are capable of producing approximately 22500 lbf of thrust, nearly a 100% increase in thrust compared to the original J-57 engines. The re-engined tanker, designated either the KC-135R (modified KC-135A or E) or KC-135T (modified KC-135Q), can offload up to 50% more fuel (on a long duration sortie), is 25% more fuel efficient, costs 25% less to operate and is 96% quieter than the KC-135A (sideline noise levels at takeoff were reduced from 126 to 99 decibels).

The KC-135R's operational range is 60% greater than the KC-135E for comparable fuel offloads, providing a wider range of basing options.

No longer in consideration, upgrading the remaining KC-135E into KC-135R would have cost about US$3 billion, about $24 million per aircraft. According to Air Force data, the KC-135 fleet had a total operation and support cost in fiscal year 2001 of about $2.2 billion. The older E model aircraft averaged total costs of about $4.6 million per aircraft, while the R models averaged about $3.7 million per aircraft. Those costs include personnel, fuel, maintenance, modifications, and spare parts.

Further upgrades and derivatives


This program adds refueling pods to the KC-135's wings. The pods allow refueling of U.S. Navy, U.S. Marine Corps and most NATO tactical jet aircraft while keeping the tail-mounted refueling boom. The pods themselves are Flight Refueling Limited (FRL) MK.32B model pods. This allows the tanker to refuel two receivers at the same time, which increases throughput compared to the boom drogue adapter.

A number of KC-135A and KC-135B aircraft have been modified to EC-135, RC-135 and OC-135 configurations for use in several different roles.

Design


The KC-135R has four turbofan engines, mounted under 35-degree swept wings, which power it to takeoffs at gross weights up to 322500 lb. 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. A boom operator stationed in the rear of the aircraft controls the boom while lying prone. 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 83000 lb of cargo.

Introduction into service


The KC-135 was initially purchased to support bombers of the Strategic Air Command, but by the late 1960s, in the Southeast Asia theater, the KC-135 Stratotanker's ability as a force multiplier came to the fore. Midair refueling of F-105 and F-4 fighter-bombers as well as B-52 bombers brought far-flung bombing targets within reach, and allowed fighter missions to spend hours at the front, rather than just a few minutes, due to their limited fuel reserves. KC-135 crews refueled both Air Force and Navy / Marine Corps aircraft, though they would have to change to probe and drogue adapters depending upon the mission. Crews also helped to bring in damaged aircraft which could fly while being fed by fuel to a landing site. KC-135s continued their tactical support role in later conflicts such as Desert Storm and current aerial strategy.

The Strategic Air Command (SAC) had the KC-135 Stratotanker in service with Regular Air Force SAC units from 1957 through 1992 and with SAC-gained Air National Guard (ANG) and Air Force Reserve (AFRES) units from 1975 through 1992. Following a major USAF reorganization that resulted in the inactivation of SAC in 1992, most KC-135s were re-assigned to the newly created Air Mobility Command (AMC). While AMC gained the preponderance of the aerial refueling mission, a small number of KC-135s were also assigned directly to United States Air Forces in Europe (USAFE), Pacific Air Forces (PACAF) and the Air Education and Training Command (AETC). All Air Force Reserve Command (AFRC) KC-135s and most of the Air National Guard (ANG) KC-135 fleet became operationally-gained by AMC, while Alaska Air National Guard and Hawaii Air National Guard KC-135s became operationally-gained by PACAF.

Air Mobility Command (AMC) manages more than 481 Stratotankers, of which the Air Force Reserve Command (AFRC) and Air National Guard (ANG) fly 292 in support of AMC's mission as on April 2008.

The KC-135 is joined by the Tupolev Tu-95, the C-130 Hercules, the B-52 Stratofortress, the English Electric Canberra, the Northrop T-38 Talon and the Lockheed U-2 in having over 50 years of continuous service with its original operator.

Research usage


Besides its primary role as an inflight aircraft refueler, the KC-135, designated NKC-135, has assisted in several research projects at the NASA Dryden Flight Research Center at Edwards Air Force Base, California. One such project occurred between 1979 and 1980 when special wingtip "winglets", developed by Richard Whitcomb of the Langley Research Center, were tested at Dryden, using an NKC-135A tanker loaned to NASA by the Air Force. Winglets are small, nearly vertical fins installed on an aircraft's wing tips. The results of the research showed that drag was reduced and range could be increased by as much as 7 percent at cruise speeds. Winglets are now being incorporated into most new commercial and military transport jets, as well as business aviation jets.

NASA also has operated several KC-135 aircraft (without the tanker equipment installed) as their infamous Vomit Comet zero-gravity simulator aircraft. The longest-serving (1973 to 1995) version was KC-135A, AF Ser. No. 59-1481, named Weightless Wonder IV and registered as N930NA.

Replacing the KC-135
As of 2006, the KC-135E fleet was flying an annual average of 350 hours per aircraft and the KC-135R fleet was flying an annual average of 710 hours per aircraft. The KC-135 fleet is currently flying double its planned yearly flying hour program to meet airborne refueling requirements, and has resulted in higher than forecast usage and sustainment costs.

The Air Force projects that E and R models have lifetime flying hour limits of 36,000 and 39,000 hours, respectively. According to the Air Force, only a few KC-135s would reach these limits before 2040, but at that time some of the aircraft would be about 80 years old. The Air Force estimates that their current fleet of KC-135s have between 12,000 to 14,000 flying hours on them-only 33 percent of the lifetime flying hour limit. Nevertheless these aircraft are over 40 years old and maintenance costs are increasing, with airframe corrosion being the worst problem.

Between 1993 and 2003, the amount of KC-135 depot maintenance work doubled, and the overhaul cost per aircraft tripled. In 1996 it cost $8,400 per flight hour for the KC-135, and in 2002 this had grown to $11,000. The Air Force’s 15-year cost estimates project further significant growth through fiscal year 2017. For example, operations and support costs for the KC-135 fleet are estimated to grow from about $2.2 billion in fiscal year 2003 to $5.1 billion (2003 dollars) in fiscal year 2017, an increase of $2.9 billion, or over 130 percent, which represents an annual growth rate of about 6.2 percent. In March 2009 the Air Force indicated that KC-135s would require additional skin replacement to allow their continued use beyond 2018.

The USAF decided to replace the KC-135 fleet. However, the KC-135 fleet is large and will need to be replaced gradually. Initially the first batch of replacement planes was to be an air tanker version of the Boeing 767, leased from Boeing. In 2003, this was changed to contract where the Air Force would purchase 80 KC-767 aircraft and lease 20 more. In December 2003, the Pentagon froze the contract and in January 2006, the KC-767 contract was canceled. This followed public revelations of corruption in how the contract was awarded, as well as controversy regarding the original leasing rather than outright purchase agreement. Then Secretary of Defense Rumsfeld stated that this move will in no way impair the Air Force's ability to deliver the mission of the KC-767, which will be accomplished by continuing upgrades to the KC-135 and KC-10 Extender fleet.

In January 2007, the U.S. Air Force formally launched the KC-X program with a request for proposal (RFP). KC-X is first phase of three acquisition programs to replace the KC-135 fleet. On 29 February 2008, the US Defense Department announced that it had selected the EADS/Northrop Grumman "KC-30" (to be designated the KC-45A) over the Boeing KC-767. On 18 June 2008, the US Government Accountability Office sustained Boeing's protest of the selection of the Northrop Grumman/EADS's tanker. In 2010, the US Air Force restarted the KC-X competition with the release of a revised request for proposal (RFP). After evaluating bids, the USAF selected the Boeing 767 design, with the military designation KC-46, as a replacement in February 2011.

Variants
See Boeing C-135 Stratolifter for further details on the C-135 family.


 * KC-135A
 * Original production version powered by four Pratt & Whitney J57s, 732 built. Given the Boeing model numbers 717-100A, 717-146 and 717-148.


 * NKC-135A
 * Test-configured KC-135A.


 * KC-135B
 * Airborne command post version with 17 built equipped with turbofan engines. Provided with in-flight refueling capability and redesignated EC-135C. Given the model number 717-166.


 * KC-135D
 * All four RC-135As (Pacer Swan) were modified to partial KC-135A configuration in 1979. The four aircraft (serial numbers 63-8058, 63-8059, 63-8060 and 63-8061) were given a unique designation KC-135D as they differed from the KC-135A in that they were built with a flight engineer's position on the flight deck. The flight engineer's position was removed when the aircraft were modified to KC-135 standards but they retained their electrically powered wing flap secondary (emergency) drive mechanism and second air conditioning pack which had been used to cool the RC-135As on-board photo-mapping systems. Later re-engined with Pratt & Whitney TF33 engines and a cockpit update to KC-135E standards in 1990 and are were retired to the 309th AMARG at Davis-Monthan AFB, AZ in 2007.


 * KC-135E
 * Air National Guard and Air Force Reserve KC-135As re-engined with Pratt & Whitney TF-33-PW-102 engines from retired 707 airliners (161 modified). All E model aircraft were retired to the 309th AMARG at Davis-Monthan AFB by September 2009 and replaced with R models.


 * NKC-135E
 * Test-configured KC-135E.


 * KC-135Q
 * KC-135As modified to carry JP-7 fuel necessary for the SR-71 Blackbird, 56 modified, survivors to KC-135T.


 * KC-135R (1960s)
 * 4 JC/KC-135As converted to Rivet Stand (Later Rivet Quick) configuration for reconnaissance and evaluation of above ground nuclear test (55-3121, 59-1465, 59-1514, 58-0126, 58-0126 replaced 59-1465 after 59-1465 crashed in 1965). These aircraft were powered by Pratt & Whitney J57 Engines and were based at Offutt AFB, Nebraska.


 * KC-135R
 * KC-135As and some KC-135Es re-engined with CFM-56 engines, at least 361 converted.


 * KC-135R(RT)
 * Receiver-capable KC-135R Stratotanker, 8 modified with either a Boeing or LTV receiver system and a secure voice SATCOM radio.


 * KC-135T
 * KC-135Q re-engined with CFM-56 engines, 54 modified.


 * EC-135Y
 * An airborne command post modified in 1984 to support CINCCENT. Aircraft 55-3125 was the only EC-135Y.  Unlike its sister EC-135N, it was a true tanker that could also receive in-flight refueling.  Pratt & Whitney TF-33-PW-102.  Currently retired to 309th AMARG at Davis-Monthan AFB, AZ.

Operators

 * Chilean Air Force operates 3, received its first KC-135E in February 2010.
 * French Air Force operates 11 C-135FRs and 3 KC-135s.
 * Republic of Singapore Air Force operates 4 KC-135R tankers, which occasionally also function as VIP transport and aeromedical missions.
 * Turkish Air Force operates 7 KC-135s.
 * Republic of Singapore Air Force operates 4 KC-135R tankers, which occasionally also function as VIP transport and aeromedical missions.
 * Turkish Air Force operates 7 KC-135s.
 * Turkish Air Force operates 7 KC-135s.
 * Turkish Air Force operates 7 KC-135s.


 * NASA (until 2004)
 * United States Air Force operates 417 KC-135s (183 Active Duty, 64 Air Force Reserve, and 170 Air National Guard).
 * United States Air Force operates 417 KC-135s (183 Active Duty, 64 Air Force Reserve, and 170 Air National Guard).


 * Air Combat Command
 * USAF Weapons School - Nellis Air Force Base, Nevada
 * 509th Weapons Squadron - Fairchild Air Force Base, Washington
 * Air Education and Training Command
 * 97th Air Mobility Wing – Altus AFB, Oklahoma
 * 54th Air Refueling Squadron
 * Air Mobility Command
 * 6th Air Mobility Wing – MacDill AFB, Florida
 * 91st Air Refueling Squadron
 * 99th Air Refueling Squadron – Birmingham IAP/ANGB (Active Associate unit)
 * 911th Air Refueling Squadron – Seymour Johnson AFB, North Carolina(Active associate unit)
 * 22d Air Refueling Wing – McConnell AFB, Kansas
 * 344th Air Refueling Squadron
 * 349th Air Refueling Squadron
 * 350th Air Refueling Squadron
 * 384th Air Refueling Squadron
 * 64th Air Refueling Squadron - Pease ANGB, New Hampshire (Active associate unit)
 * 92d Air Refueling Wing – Fairchild AFB, Washington
 * 92d Air Refueling Squadron
 * 93d Air Refueling Squadron
 * 912th Air Refueling Squadron - March ARB, California (Active associate unit)
 * 375th Air Mobility Wing – Scott AFB, Illinois
 * 906th Air Refueling Squadron (Active associate unit)
 * Pacific Air Forces
 * 18th Wing – Kadena AB, Japan
 * 909th Air Refueling Squadron
 * United States Air Forces in Europe
 * 100th Air Refueling Wing – RAF Mildenhall, England
 * 351st Air Refueling Squadron
 * Air Force Reserve Command
 * 434th Air Refueling Wing – Grissom ARB, Indiana
 * 72d Air Refueling Squadron
 * 74th Air Refueling Squadron
 * 452d Air Mobility Wing – March ARB, California
 * 336th Air Refueling Squadron
 * 459th Air Refueling Wing – Andrews AFB, Maryland
 * 756th Air Refueling Squadron
 * 507th Air Refueling Wing – Tinker AFB, Oklahoma
 * 18th Air Refueling Squadron – McConnell AFB, Kansas
 * 465th Air Refueling Squadron
 * 916th Air Refueling Wing – Seymour Johnson AFB, North Carolina
 * 77th Air Refueling Squadron
 * 927th Air Refueling Wing – MacDill AFB, Florida
 * 63d Air Refueling Squadron


 * Air National Guard
 * Alabama Air National Guard
 * 117th Air Refueling Wing – Birmingham IAP/ANGB
 * 106th Air Refueling Squadron
 * Alaska Air National Guard
 * 168th Air Refueling Wing – Eielson AFB
 * 168th Air Refueling Squadron
 * Arizona Air National Guard
 * 161st Air Refueling Wing – Sky Harbor IAP/ANGB
 * 197th Air Refueling Squadron
 * Hawaii Air National Guard
 * 154th Wing – Hickam AFB
 * 203d Air Refueling Squadron
 * Illinois Air National Guard
 * 126th Air Refueling Wing – Scott AFB
 * 108th Air Refueling Squadron
 * Iowa Air National Guard
 * 185th Air Refueling Wing – Sioux Gateway ANGB
 * 174th Air Refueling Squadron
 * Kansas Air National Guard
 * 190th Air Refueling Wing – Forbes Field ANGB
 * 117th Air Refueling Squadron
 * Maine Air National Guard
 * 101st Air Refueling Wing – Bangor IAP/ANGB
 * 132d Air Refueilng Squadron
 * Michigan Air National Guard
 * 127th Wing – Selfridge ANGB
 * 171st Air Refueling Squadron
 * Mississippi Air National Guard
 * 186th Air Refueling Wing – Key Field ANGB
 * 153d Air Refueling Squadron
 * Nebraska Air National Guard
 * 155th Air Refueling Wing – Lincoln ANGB
 * 173rd Air Refueling Squadron
 * New Hampshire Air National Guard
 * 157th Air Refueling Wing – Pease ANGB
 * 133d Air Refueling Squadron
 * New Jersey Air National Guard
 * 108th Air Refueling Wing – McGuire AFB
 * 141st Air Refueling Squadron
 * 150th Air Refueling Squadron
 * Ohio Air National Guard
 * 121st Air Refueling Wing – Rickenbacker ANGB
 * 145th Air Refueling Squadron
 * 166th Air Refueling Squadron
 * Pennsylvania Air National Guard
 * 171st Air Refueling Wing – Pittsburgh International Airport/Pittsburgh ARS
 * 146th Air Refueling Squadron
 * 147th Air Refueling Squadron
 * Tennessee Air National Guard
 * 134th Air Refueling Wing – McGhee Tyson ANGB
 * 151st Air Refueling Squadron
 * Utah Air National Guard
 * 151st Air Refueling Wing – Salt Lake City International Airport/ANGB
 * Washington Air National Guard
 * 141st Air Refueling Wing – Fairchild AFB
 * 116th Air Refueling Squadron
 * Wisconsin Air National Guard – General Mitchell International Airport
 * 128th Air Refueling Wing

Note Italy has been reported in some sources as operating several KC-135s, however these are actually Boeing 707-300s converted to tanker configuration.

Israel was offered KC-135s again in 2013, after turning down the ancient aircraft twice due to expense of keeping them flying. The IAF again rejected the offered KC-135Es, but said that it would consider as many as a dozen of the newer KC-135Rs.

Accidents

 * On 27 June 1958, USAF KC-135A, serial number 56-3599, stalled and crashed at Westover Air Force Base after the crew failed to retract the flaps on takeoff, killing all 15 on board. The aircraft was attempting a world speed record between New York and London.
 * On 31 March 1959, USAF KC-135A, 58-0002, entered a thunderstorm near Killeen, Texas. Two engines separated and one of the engines struck the tail, causing loss of control. The aircraft crashed on a hillside, killing all four crew on board. The aircraft had been delivered just six weeks before the accident.
 * On 15 October 1959, USAF KC-135A, 57-1513, collided in mid-air with B-52F 57-0036 at 32,000 feet over Leitchfield, Kentucky, killing all six on board both aircraft.
 * On 3 February 1960, USAF KC-135A, 56-3628, crashed on takeoff in extremely gusty crosswind conditions at Roswell-Walker AFB, NM. The airplane skidded into two other KC-135 tankers (57-1449 and 57-1457) and a hangar and burst into flames.  The aircraft was on a training flight, but the instructor pilot was occupying the jump seat instead of one of the pilot seats as directed by the local commander.  The destruction of three aircraft, along with six fatalities among the crew and an additional two on the ground made this a unique mishap.
 * On 18 November 1960, USAF KC-135A, 56-3605, crashed on landing at Loring Air Force Base due to an excessive sink rate, killing one of 17 on board.
 * On 9 May 1962, USAF KC-135A, 56-3618, crashed on takeoff from Loring Air Force Base due to engine failure, killing all six on board.
 * On 10 September 1962, USAF KC-135A, 60-0352 on a flight from Ellsworth Air Force Base to Fairchild Air Force Base crashed into a mountain just 20 miles (32 km) northeast of Spokane, Washington. The flight hit fog on approach to the airbase and hit Mount Kit Carson, a 5271 ft mountain. The crash killed all four crew and 40 passengers on board.
 * On 27 February 1963, USAF KC-135A, 56-3597, crashed on takeoff at Eielson Air Force Base due to engine separation, killing all seven on board; two on the ground died when debris from the crash struck a guard house and nearby waiting room.
 * On 21 June 1963, USAF KC-135A-BN Stratotanker, 57-1498 out of Westover AFB crashed on approach during a training flight in a wooded area near Belchertown, MA. One of the four occupants was killed.
 * On 28 August 1963, USAF KC-135A, 61-0322, collided in mid-air with KC-135A 61-0319 in the so-called Bermuda Triangle, killing all 11 on board both aircraft.
 * On 8 July 1964, USAF KC-135A, 60-0340, collided in mid-air with F-105 Thunderchief 61-0091 during in-flight refueling over Death Valley, California, killing all five on board both aircraft.
 * On 4 January 1965, USAF KC-135A, 61-0265, crashed on climbout from Loring Air Force Base after two engines separated, killing all four on board.
 * On 16 January 1965, USAF KC-135A 57-1442, crashed after an engine failure shortly after take off from McConnell Air Force Base, Kansas. The fuel laden plane crashed at a street intersection and caused a huge fire. A total of 30 were killed, including 23 on the ground and the seven member crew.
 * On 26 February 1965, USAF KC-135A, 63-8882, collided in mid-air with B-47E 52-0171 over the Atlantic Ocean, killing all eight on board both aircraft.
 * On 3 June 1965, USAF KC-135A, 63-0842, lost electrical power on takeoff and crashed at Walker Air Force Base, killing all five on board.
 * On 19 May 1966, USAF KC-135A, 57-1444, of 4252nd Strategic Wing, crashed on takeoff from Kadena Air Base, killing all 11 on board as well as a motorist on nearby Highway 16. The aircraft was bound for Yokota Air Base to repair a KC-135 when it lifted off too soon during a heavy-weight takeoff.
 * On 17 January 1966, a fatal collision occurred between a B-52G, 58-0256, and a KC-135A, 61-0273, flying out of Moron AB, Spain while flying over Palomares, Spain.  The B-52G was on an Operation Chrome Dome mission, which required multiple air refuelings.    The mishap caused both aircraft to break up in mid-air and killed all four crewmembers on the KC-135A and three of the seven on the B-52G, while causing radiological contamination as well as a nuclear weapon which had to be recovered from the sea nearby.
 * On 19 January 1967, USAF KC-135A, 56-3613, crashed into Shadow Mountain (elevation 4,340 ft MSL) while descending towards Fairchild Air Force Base, killing all nine on board.
 * On 17 July 1967, USAF KC-135R, 59-1465, stalled and crashed near Offutt Air Force Base after the pilot overrotated the aircraft during takeoff, causing a stall and killing one of five on board in the subsequent crash.
 * On 17 January 1968, USAF KC-135A, 58-0026, stalled and crashed at Minot Air Force Base after the pilot, 15th Air Force Vice Commander MGen Charles Eisenhart, overrotated the aircraft during takeoff in a snowstorm, killing all 13 on board. This accident was instrumental in the decision to refit the KC-135 fleet with the Collins FD-109(V) integrated flight director system, in place of the earlier "round dial" cockpit layout.
 * On 30 July 1968, USAF KC-135A, 56-3655, crashed on Mount Lassen after the vertical stabilizer broke off after a sharp turn while practicing an emergency descent, killing all nine on board.
 * On 1 October 1968, USAF KC-135A, 55-3138, struck concrete and steel light poles on takeoff and crashed at U-Tapao Airport, Thailand after a loss of power in an engine and resultant loss of control, killing all four on board.
 * On 22 October 1968, USAF KC-135A, 61-0301, flew into a mountain while descending to Ching Chuan Air Base, Taiwan, killing all six on board.
 * On 19 December 1969, USAF KC-135A, 56-3629, crashed into the sea on climbout from Ching Chuan Kang Air Base due to low-level windshear, killing all four on board.
 * On 3 June 1971, USAF KC-135Q, 58-0039, exploded in mid-air and crashed at Centenera, Spain, killing all five on board.
 * On 8 March 1973, USAF KC-135A, 63-7989, collided with KC-135 63-7980 on the ramp at Lockbourne Air Force Base and caught fire, killing two of five on board.
 * On 6 February 1976, USAF KC-135A, 60-0368, flew into a mountain while descending to Torrejon Air Base, Spain, killing all seven on board. The aircraft was assigned to the 410th BMW/46th AREFS at K.I. Sawyer AFB, Michigan, but, as is often the case on Tanker Task Force deployed operations, the flight crew was from another SAC unit at Seymour-Johnson AFB, NC.  Only two aircraft crew chiefs onboard were from K I Sawyer AFB, MI.
 * On 26 September 1976, USAF KC-135A, 61-0296, crashed while on approach to Wurtsmith Air Force Base, Michigan, killing 15 passengers and flight crew on board. The aircraft was flying a "First Team" mission taking 10 passengers to HQ-Strategic Air Command for briefings and orientation.  The crew became distracted by a cabin pressurization problem after an intermediate stop and descended into a wooded area about 12 miles southwest of Alpena, Michigan.  There was one survivor, reportedly a crew chief who was in the boom operator aft station (boom pod) at the time of the crash.
 * On 13 March 1982, Arizona ANG KC-135A, 57-1489. collided in mid-air with a civilian Grumman-American AA-1 Yankee near Luke AFB, AZ. The collision, which occurred as the tanker descending on an IFR flight plan through an undercast and was struck by the civilian aircraft operating VFR just below the cloud deck, caused the tail of the KC-135 to be severed by the force of the impact.  The two civilians on the AA-1 and four military personnel on the KC-135 were killed, included among the dead was the squadron commander of the 197th AREFS, Lt Col James N. Floor.
 * On 19 March 1982, USAF KC-135A, 58-0031, exploded in mid-air at 13,700 feet and crashed at Greenwood, Illinois, due to a possible overheated fuel pump, killing all 27 on board.
 * On 17 June 1986, USAF KC-135A,63-7983, crashed into the nearby hills of Howard AFB, Panama after a failed landing attempt. All four crew members on-board were killed. The crew and tanker were based out of Grissom Air Force Base in Indiana.
 * On 13 March 1987, USAF KC-135A, 60-0361, crashed at Fairchild Air Force Base after encountering wake turbulence from a B-52, while practicing a low-level refueling display. The aircraft rolled 80 degrees to the left, which stalled both left side engines (#1 and #2).  The crew was able to recover to wings level, but were too low and impacted the ground in an open area of the base.  The accident killed all six on board and one person on the ground.
 * On 20 September 1989, USAF KC-135E, 57-1481, exploded on the ground at Eielson Air Force Base due to an overheated fuel pump, killing two of seven on board. The crew was shutting down the engines when the explosion occurred.
 * On 4 October 1989, a KC-135A Stratotanker, 56-3592, from en route from Loring Air Force Base crashed into a hill along the west side of Trans-Canada Highway 2 2 mi north of Perth-Andover, New Brunswick in Carlingford, New Brunswick due to an overheated fuel pump, killing all four crew members. After five accidents involving fuel pump overheating, crews were to keep 3000 pounds of fuel in the tank.
 * On 31 January 1989, a USAF KC-135A, 63-7990, crashed on takeoff from Dyess AFB, TX after the water-injection system for the Pratt & Whitney J-57 engines failed and the remaining "dry" thrust was insufficient for flight at the takeoff gross weight. The mission was scheduled as a non-stop flight to Hickam AFB/Honolulu HI with an en route F-16 air refueling mission.  In addition to the 7 crewmembers, 12 passengers, including military spouses, retired military members and one child, were killed.   The aircraft was based at K I Sawyer AFB, MI.
 * On 13 January 1999, a Washington Air National Guard KC-135E, 59-1452, crashed on approach in Geilenkirchen, Germany due to the horizontal stabilizer being in a 7.5 nose-up trim condition, killing 4 crew members.
 * On 26 September 2006, a USAF KC-135R, 63-8886, was damaged beyond economical repair when it was struck by a Tupolev 154 of Altyn Air EEX-85718) while stopped on a taxiway after landing at Manas Airbase. The Tu-154 was taking off and its right wing struck the fairing of the KC-135R No. 1 engine.  The force of the impact nearly severed the No. 1 engine, but destroyed a portion of the left wing and the resulting fire caused extensive damage to the KC-135. The Tu-154 lost about 6 feet of its right wingtip, but was able to get airborne and return to the airport for an emergency landing. The tanker crew had been directed to use a taxiway which was not usable for night operations and the controller failed to note that they reported "holding short" of that taxiway, rather than "clear of" that point. The crew of the KC-135 evacuated the aircraft without serious injuries.
 * On 3 May 2013, a Fairchild AFB, WA air crew flying a McConnell AFB, Ks (USAF) KC-135R, 63-8877, crashed about 8 minutes after taking off from Manas Airbase in Kyrgyzstan, killing three crew members. The aircraft was at cruise altitude about 200 km west of Bishkek when it lost altitude and crashed in a mountainous area near the village of Chorgolu, close to the border between Kyrgyzstan and Kazakhstan. Videotape evidence seems to indicate that the fuselage was in flames as it descended from the clouds overhead, although the tail and some wreckage (left wing, vertical stabilizer, one engine, boom and boom drogue adapter) were not blackened by fire and landed some distance away.  This may indicate an inflight explosion or structural failure, possibly related to thunderstorms in the area.  l  Although one of the last -135 aircraft built, this airframe was 48 years and 10 months old at the time of its loss.