Report to Congressional Requesters

United States General Accounting Office 

GAO

June 2004 MILITARY AIRCRAFT

DOD Needs to 

Determine Its Aerial 

Refueling Aircraft 

Requirements 

GAO-04-349 
www.gao.gov/cgi-bin/getrpt?GAO-04-349.

To view the full product, including the scope 

and methodology, click on the link above. 

For more information, contact Neal Curtin at 

(757) 552-8100 or curtinn@gao.gov.. 

Highlights of GAO-04-349, a report to 

congressional requesters 

June 2004

MILITARY AIRCRAFT

DOD Needs to Determine Its Aerial 

Refueling Aircraft Requirements 

The current refueling force has successfully supported the needs of U.S. 

combat and mobility air forces during peacetime and wartime operations but 

future support costs will continue to rise as the fleet continues to age, 

according to the Air Force. Congress authorized the Air Force to acquire 100 

KC-767A aerial refueling aircraft in November 2003 as the first step in 

replacing the 538-plane KC-135 fleet but it could take up to 30 years to 

replace the rest based on the estimated production rate for the first 100 

aircraft. Thus, the Air Force will need to continue maintaining and 

modernizing some of the remaining aircraft for up to 3 decades. Some of 

those aircraft could be 70 to 80 years old when they are eventually replaced. 

DOD does not know how many or what type of aircraft are needed to meet 

future refueling needs because its requirements study is out of date. The 

most recent study, Tanker Requirements Study-05, was done in 2001 and 

identified the number of aircraft needed to carry out a two-major-theaterwar strategy. However, that strategy has been superceded by a new 

capabilities-based approach contained in the 2001 Quadrennial Defense 

Review. In addition, significant changes taking place in operational 

concepts and force structure could substantially affect future refueling 

requirements. As a result, the Air Force does not have a clear picture of 

future needs that could guide its replacement and investment decisions. 

GAO outlines three broad options (see table below) to meet the Air Force’s 

long-term aerial refueling requirements. DOD could adopt one or a 

combination of these approaches. GAO is not taking a position on which 

option(s) would be most suitable. The Air Force was recently directed by 

DOD to conduct and complete by August 2005 an analysis of alternatives for 

replacing the current capability. However, at the time of our audit work, the 

Air Force did not plan to study the option of using contractor-provided aerial 

refueling services as part of its analysis of alternatives. 

Options for Meeting Aerial Refueling Requirements 

Option Considerations 

Acquire new aircraft 

This could be a commercial derivative or new development; 

could consider various types and sizes of aircraft, including 

potential unmanned aircraft of the future. 

Acquire used aircraft and convert to 

tankers 

Numerous types of used commercial aircraft are available, 

but the condition and age of the planes, along with the cost 

to convert them to tankers, would need careful study. 

Contract for refueling services 

The Navy uses contracting on a limited basis. Contracting 

could meet some portion of refueling needs. 

Source: GAO. 

With the heavy pace of operations 

in support of the war on terrorism, 

the Department of Defense (DOD) 

and the Air Force have become 

increasingly concerned about their 

aging aerial refueling aircraft. We 

last reviewed the aerial refueling 

fleet in 1996 and found that KC-135 

aircraft were aging and becoming 

increasingly costly to maintain and 

operate. In December 2001, we 

began new work on the Air Force’s 

requirements for refueling aircraft. 

However, we suspended our work 

several times to provide testimony 

and other products on the 

condition of the current fleet and 

Air Force plans to accelerate 

replacement. We were asked to 

review (1) the extent to which the 

current fleet has met aerial 

refueling needs, and the cost and 

effort to operate and sustain the 

fleet, (2) DOD's current refueling 

requirements, and (3) options to 

meet future aerial refueling needs. 

We recommend that the Secretary 

of Defense (1) conduct a study to 

determine the current and 

projected aerial refueling 

requirements, and (2) direct that 

the planned analysis of alternatives 

be a comprehensive study of all 

reasonably available options or 

options currently being tested, 

including using contractorprovided aerial refueling services. 

DOD concurred with each 

recommendation and had begun 

the studies at the time of this 

report. 
Page i GAO-04-349 Military Aircraft 

Letter 1

Results in Brief 3

Background 4

Current Force Has Met Refueling Needs but at Increasing Cost and 

Effort 9

Air Force’s Aerial Refueling Requirements Are Outdated 17

Three Options Exist to Meeting the Air Force’s Future Aerial 

Refueling Requirements 24

Conclusions 29

Recommendations for Executive Action 29

Agency Comments and Our Evaluation 30

Appendix I Scope and Methodology 31 

Appendix II Comments from the Department of Defense 33 

Appendix III GAO Contact and Staff Acknowledgments 35 

Related GAO Products 36 

Tables 

Table 1: Air Force Aerial Refueling Statistics for Major Conflicts 

Since 1991 10

Table 2: Distribution of Flying Hours for the KC-135 Fleet 

(Fiscal Years 1996-2002) 10

Table 3: KC-135 Operating and Support Costs (Fiscal Years 

1996-2002) 13

Table 4: Number of Air Force Aerial Refueling Aircraft in the Fleet 

Expressed as KC-135R Aircraft Equivalents 19

Table 5: Changes to National Strategies and Operational Concepts 

That Could Lead to Changed Aerial Refueling 

Requirements 21

Contents 
Page ii GAO-04-349 Military Aircraft 

Figures 

Figure 1: KC-10 Aerial Refueling Aircraft Preparing to Refuel an 

F-16 Fighter 5

Figure 2: KC-135 Aerial Refueling Aircraft 6

Figure 3: Removal and Replacement of KC-135 Fuselage Skin 12

Figure 4: Example of a Cracked Frame Component That Was 

Replaced During Programmed Depot Maintenance 14

Figure 5: Trend in the Number of Depot Flow Days for 

Programmed Depot Maintenance Per KC-135 Aircraft 

(Fiscal Years 1991-2000) 16

Abbreviation 

DOD Department of Defense 

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Page 1 GAO-04-349 Military Aircraft 

June 4, 2004

The Honorable Duncan Hunter 

Chairman 

Committee on Armed Services 

House of Representatives 

The Honorable Joel Hefley 

Chairman 

Subcommittee on Readiness 

Committee on Armed Services 

House of Representatives 

Aerial refueling is critical to U.S. national security strategy, allowing 

bomber, fighter, and transport aircraft to rapidly deploy and operate 

globally, stay airborne longer, and carry more weapons, equipment, and 

supplies. The Air Force has most of the Department of Defense’s (DOD) 

refueling capability in 59 large KC-10 and 538 KC-135 aerial refueling 

aircraft. The KC-135 aircraft averages about 43 years of age—the oldest 

aircraft in the military inventory. Following the terrorist attacks of 

September 11, 2001, and the start of the global war on terrorism, DOD and 

the Air Force have become increasingly concerned about possible agerelated problems that could ground the refueling fleet. The Air Force 

believes the national security strategy cannot be executed without aerial 

refueling. 

We last reviewed the aerial refueling fleet in 19961

 and concluded that the 

KC-135 aircraft were aging and becoming increasingly costly to maintain 

and operate. We also pointed out that DOD had a need for more mobility 

aircraft to transport troops and equipment to theaters of operations. 

Consequently, we recommended that when DOD considers a replacement 

for the KC-135 aircraft, it develop a multi-role aircraft that could do aerial 

refueling or airlift operations. DOD responded that it could operate the 

KC-135 aircraft for another 35 years, to approximately 2030, when they 

would be 70 to 80 years old. However, since 2001, DOD and the Air Force 

have accelerated plans to begin replacing the KC-135 aircraft. They will be 

expensive to replace and will likely require many years of effort given the 

number of aircraft to be replaced and the high cost of military aircraft. In 

 1

 U.S. General Accounting Office, U.S. Combat Air Power: Aging Refueling Aircraft Are 

Costly to Maintain and Operate, GAO/NSIAD-96-160 (Washington, D.C.: Aug. 8, 1996). 

United States General Accounting Office 

Washington, DC 20548 
Page 2 GAO-04-349 Military Aircraft 

December 2001, we were requested to review the Air Force’s requirements 

for aerial refueling aircraft and options to meet those requirements. We 

received the request and began the work before the Air Force announced 

that it planned to lease Boeing 767 aircraft modified for aerial refueling. 

We suspended this work several times to provide testimony and other 

products related to the condition of the current refueling fleet and the 

specific terms of the proposed lease in 2002 and 2003 (see p. 35 of this 

report for a list of GAO aerial refueling aircraft-related products, including 

our testimony statements). We have now completed our work on the 

original request and this report is the result. As requested, we examined, 

(1) the extent to which DOD’s current aerial refueling force has met 

refueling needs, and the cost and effort associated with operating and 

sustaining the current fleet; (2) the most recent aerial refueling 

requirements; and (3) options to enable DOD to meet future aerial 

refueling requirements. Subsequent to this request, in 2002, Congress 

authorized the Secretary of the Air Force to initiate a multi-year pilot 

program to lease up to 100 Boeing 767 aircraft for use as aerial refueling 

aircraft. Subsequent to the hearings, Congress amended the authorization 

to permit the Air Force to lease 20 and purchase 80 aerial refueling 

aircraft. 

To examine the extent to which DOD’s current aerial refueling force has 

met mission requirements, the cost of maintenance, and efforts to sustain 

the fleet, we interviewed DOD and Air Force officials and reviewed key 

documents, comparing mission requirements and aerial refueling aircraft 

availability rates; and obtained a variety of data documenting maintenance 

costs. We did not independently verify the reliability of the cost and 

maintenance data, but we discussed cost estimates with certain internal 

and external organizations knowledgeable about aircraft operating and 

maintenance costs to determine the reasonableness of the data, and we 

determined that the estimates were reasonable. To examine current aerial 

refueling aircraft requirements, we interviewed key DOD and Air Force 

officials and reviewed key requirements documents, including a joint 

instruction calling for a requirements determination study and 

recommending an analysis of alternatives to meeting the requirements, a 

briefing on Tanker Requirements Study-05, and the complete Mobility 

Requirements Study-05. To identify options to enable DOD to meet the 

requirements, we interviewed officials and obtained documents outlining 

three different approaches to meeting refueling requirements that are 

generally considered to be reasonably available in the near term. We 

describe our scope and methodology in appendix I. We conducted this 

work from December 2001 to April 2004 in accordance with generally 

accepted government auditing standards. 
Page 3 GAO-04-349 Military Aircraft 

The current refueling force has met the needs of U.S. forces in peacetime 

and wartime; however, future costs and efforts needed to operate and 

support the existing refueling fleet, especially the KC-135s, will likely 

continue to rise as these aircraft age. Although Congress has authorized 

the Air Force to lease 20 and purchase 80 KC-767A aerial refueling aircraft 

to start replacing the 538-plane KC-135 fleet, the Air Force will likely need 

another 20 to 30 years to replace the rest based on the planned production 

rate of the first 100 aircraft and the likely cost of the planes. Consequently, 

the Air Force will need to maintain and possibly modernize at least some 

of the remaining aircraft for up to 3 decades. Some of those aircraft could 

be between 70 to 80 years old when replaced. 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 (fiscal year 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. 

Currently, the Air Force does not know how many aircraft or the type of 

aircraft needed for the future refueling mission because no up-to-date 

studies exist to validate the number or type needed. Tanker Requirements 

Study-05 is the most recent study, but it specifies the number of refueling 

aircraft needed to support operations contemplated in the outdated 

two-major-theater-war strategy. The current strategy is the 2001 

Quadrennial Defense Review approach to (1) defend the homeland, 

(2) deter aggression by maintaining regionally tailored forces, (3) swiftly 

defeat aggression in two overlapping major conflicts, and (4) decisively 

defeat the adversary in one of two major conflicts. The current strategy, 

combined with the global war on terrorism, and DOD reassessments of 

operational concepts and the force structure may lead to still more 

changes in planned operations and by extension, in refueling support that 

will be required, although no requirements study was planned to replace 

Tanker Requirements Study-05 at the time of our audit work. DOD 

guidance also specifies that an analysis of alternatives is required to 

identify options for meeting requirements.2

 The Fiscal Year 2004 National 

Defense Authorization Act required an analysis of alternatives to identify 

options best suited to meeting current and projected refueling needs by no 

later than March 1, 2004. To comply with the mandated requirement, DOD 

has completed an interim report memorandum dated February 24, 2004, 

 2

 An analysis of alternatives evaluates the operational effectiveness, suitability, and 

estimated costs of alternative systems to meet a mission capability. It assesses the 

advantages and disadvantages of the alternatives being considered, including the sensitivity 

of each alternative to possible changes in key assumptions. 

Results in Brief 
Page 4 GAO-04-349 Military Aircraft 

outlining the framework and parameters it proposes for the Air Force to 

use in an overview study of various options for replacing its aging fleet of 

KC-135 aircraft. However, DOD and the Air Force recognize that the 

February 2004 guidance letter is not an analysis of alternatives. DOD plans 

to issue a separate analysis and report studying the material condition of 

its fleet of KC-135 aerial refueling aircraft by September 2004, followed by 

the analysis of alternatives study to be issued in August 2005. 

At least three options exist to meet future refueling needs. The Air Force 

could (1) directly acquire new aircraft to replace the KC-135 fleet, 

(2) obtain excess commercial aircraft configured for refueling, or 

(3) augment its fleet with contractor-provided refueling. Except for the 

option to directly acquire new aircraft, these options or some combination 

could enable DOD to meet refueling needs without incurring the full cost 

to acquire, operate, and support a new refueling fleet and develop required 

associated infrastructure. DOD’s planned analysis of alternatives will 

review options related to buying new or commercially similar aircraft as 

well as acquiring and modifying used aircraft but was not planned to 

evaluate the potential for contractor-provided refueling, according to the 

memorandum from the Office of the Secretary of Defense to the Air Force 

directing that an analysis of alternatives be done. We are not taking a 

position on which option(s) would be more suitable. 

To provide a current, comprehensive roadmap to guide long-term 

replacement of the current tanker fleet, we recommend that the Secretary 

of Defense (1) conduct a new, validated requirements study to determine 

current and projected aerial refueling requirements and (2) expand the 

planned analysis of alternatives to include all viable options for providing 

aerial refueling including the potential for the use of contractors. DOD 

concurred with each recommendation and had begun the studies at the 

time of this report. 

Aerial refueling is critical to carrying out U.S. national security strategy 

because it allows other aircraft to fly further, stay airborne longer, and 

carry more weapons, equipment, and supplies. The Air Force has stated 

that without aerial refueling, U.S. national security strategy could not be 

executed. While numerous military aircraft are used for refueling, most of 

the U.S. refueling capability is in the Air Force’s 59 KC-10 and 538 KC-135 

aircraft. These large, long-range aircraft are based on commercial aircraft 

modified for aerial refueling. The KC-10 aircraft is based on the DC-10 

commercial aircraft, was built in the 1980s and averages about 20 years in 

age. Figure 1 displays a KC-10 aircraft refueling an F-16 fighter aircraft. 

Background 
Page 5 GAO-04-349 Military Aircraft 

Figure 1: KC-10 Aerial Refueling Aircraft Preparing to Refuel an F-16 Fighter 

In addition to its refueling capability, the KC-10 is a multi-role aircraft and 

can be used to transport air cargo, known as airlift. 

The KC-135 aircraft, similar to the Boeing 707 commercial airliner, was 

built in the 1950s and 1960s, and aircraft still in the fleet average about 43 

years in age. Figure 2 displays a KC-135 refueling aircraft. 

Source: Air Force.
Page 6 GAO-04-349 Military Aircraft 

Figure 2: KC-135 Aerial Refueling Aircraft 

In terms of refueling capacity, the KC-135 aircraft comprise about 

90 percent of the refueling fleet and consequently are the mainstay of the 

U.S. aerial refueling capability.3

 However, their ability to meet current and 

future refueling mission requirements will depend on continued 

maintenance, support, and operations for years to come. 

 3

 There are two basic versions of the KC-135 aircraft today—the KC-135R and the 

KC-135E—both of which were derived from the original KC-135As produced in the 1950s 

and 1960s. The Air Force undertook a two-pronged engine replacement program in the 

mid-1980s to improve the performance of its then 20- to 30-year-old KC-135A refueling fleet. 

First, over 155 Air National Guard and Air Force Reserve tankers were modified with used 

commercial airline engines, which improved their fuel offload capability by 20 percent, and 

their fuel efficiency by 14 percent. These aircraft were redesignated as KC-135Es. During 

this same period, active duty aircraft received new, more powerful, efficient CFM-56 

commercial engines plus about 25 other improvements (such as reinforced floors and wing 

structures and strengthened landing gear), which enabled the modified aircraft—

redesignated as KC-135Rs—to offload 50 percent more fuel, reduce fuel consumption by 

25 percent, and operate 96 percent quieter than the KC-135As. Subsequently, some of the 

KC-135Es were also modified to KC-135Rs, so that as of March 1, 2004, there were 417 

KC-135Rs and 121 KC-135Es. All active duty Air Force units only operate the KC-135Rs, as 

do some Air National Guard and Air Force Reserve units, while all of the KC-135Es are 

assigned to Air National Guard and Air Force Reserve units. Over half of the total 538-plane 

KC-135 fleet is assigned to Air National Guard and Air Force Reserve units. 

Source: Air Force.
Page 7 GAO-04-349 Military Aircraft 

Between 1996 and November 2001, DOD and the Air Force expressed little 

urgency to replace KC-135 aircraft even though the aircraft were 

experiencing age-related problems. For example, the Air Force was 

addressing corrosion, increased operating and support costs, and reduced 

aircraft availability in the mid-1990s, when we last reviewed aerial 

refueling issues.4 In our 1996 report, we stated that (1) the KC-135 aircraft 

was becoming increasingly costly to maintain and operate, 

(2) procurement of a commercial-derivative aircraft could take 4 to 6 years 

and development of a new aircraft could take up to 12 years, and (3) the 

Air Force would need to quickly initiate studies to develop a replacement 

strategy for mobility aircraft used in aerial refueling and airlift. DOD 

responded that “while the KC-135 is an average of 35 years old, its airframe 

hours and cycles are relatively low. With proper maintenance and 

upgrades, we believe the aircraft may be sustainable for another 35 years.” 

Thus, DOD planned to continue operating the aircraft until about 2030, 

when they would be about 70 to 80 years old. 

At that same time, the Air Mobility Command deferred the start of KC-135 

replacement from fiscal year 2007 to fiscal year 2013. Moreover, in 

November 2001, the commander of the Air Mobility Command stated that 

the “Air Mobility Command’s priority is to continue with C-17 acquisition 

and C-5 modernization in the near term. As the airlift priority is met, AMC 

will begin to shift resources to address the next air refueling platform in 

the mid-to-long-term. Air Mobility Strategic Plan 2000 envisions KC-135 

aircraft retirement beginning in 2013 with the concurrent fielding of a 

replacement air refueling platform.” 

In January 2002,5

 Congress authorized a pilot program to lease 100 Boeing 

767 aircraft modified for aerial refueling, subsequently designated the 

KC-767A aircraft. At about the time that Congress authorized the proposed 

lease, the Air Force position on when it wanted to begin retiring KC-135s 

and introducing replacement aircraft shifted from around 2013 to 2006. 

The Air Force stated that the urgency was due to growing operating and 

support costs, declining aircraft availability, and an increasing possibility 

that a fleetwide grounding event would prevent continued operation of the 

 4

 U.S. General Accounting Office, U.S. Combat Air Power: Aging Refueling Aircraft Are 

Costly to Maintain and Operate, GAO/NSIAD-96-160 (Washington, D.C.: Aug. 8, 1996). 

5

 Department of Defense and Emergency Supplemental Appropriations for Recovery from 

and Response to Terrorist Attacks on the United States Act, 2002, Pub. L. No. 107-117, 

§ 8159, 115 Stat. 2230, 2284-85 (2002). 

Prior to 2001 neither DOD 

nor the Air Force 

Expressed an Urgent Need 

for a New Refueling 

Aircraft 
Page 8 GAO-04-349 Military Aircraft 

KC-135 aircraft and thus cripple refueling support to U.S. combat air 

forces. In mid-2003, the Air Force introduced a plan to retire 61 KC-135Es, 

to reduce the support costs while increasing the number of crews, flying 

hours, and utilization rates for the remaining aircraft.6

 The fiscal year 2004 

defense authorization act limited the number of KC-135Es to be retired in 

that fiscal year to 12 aircraft. 

Despite the recently stated urgency of replacing the KC-135 aircraft, the 

Air Force has not requested funds in the fiscal year 2005 budget to buy or 

lease new refueling aircraft. In a traditional procurement, the Air Force 

would need to have programmed any funding to buy the new aircraft. On 

the other hand, a key claimed advantage of the proposed lease was that 

the Air Force could immediately order the KC-767A aircraft for delivery 

beginning in 2006 but would only have to make annual payments to the 

aircraft owner rather than paying the full purchase price. Conversely, if the 

Air Force replaced the refueling aircraft through a purchase, it would have 

had to program sufficient funds to pay the full purchase price by 2006 for 

delivery beginning in 2009. However, neither DOD nor the Air Force 

wanted to reprogram funds from other acquisition programs to accelerate 

refueling aircraft procurement because such action was thought to have 

the potential to disrupt other programs and affect military capability. 

In 2003, the House and Senate Armed Services Committees held hearings 

on the condition of the KC-135 fleet and proposed leasing of 100 KC-767A 

aircraft. Subsequent to the hearings and in the National Defense 

Authorization Act for Fiscal Year 2004, Congress amended the original 

lease provision and authorized the Air Force to lease 20 new KC-767A 

aircraft and purchase 80. A key advantage of this plan is that it offered 

savings of about $5 billion in current dollars over the plan to lease all 100 

aircraft but also requires the Air Force to pay for the 80 aircraft sooner 

than if they were leased. However, at the time of this report, the combined 

lease and purchase had not yet been initiated. DOD has placed the final 

contract signing for the combined lease and purchase on hold until the 

DOD Inspector General completes a review of the actions of Air Force and 

Boeing officials during negotiations, and until the Defense Science Board 

 6

 Seven additional KC-135E aircraft will be moved to back-up aircraft inventory, which 

allows the Air Force to conduct scheduled and non-scheduled maintenance, modifications, 

inspections, and repair on these aircraft without a corresponding reduction of aircraft 

available for operational missions. 

Status of KC-767A Aircraft 

Acquisition 
Page 9 GAO-04-349 Military Aircraft 

completes a review of the condition of the KC-135 fleet, expected in 

September 2004. 

DOD’s aerial refueling force has met the needs of U.S. combat and mobility 

air forces since 1991.7 However, as the fleet ages, the costs and the efforts 

to keep it operating safely are likely to grow. Although the Air Force has 

begun the process to replace all 121 KC-135E aircraft with 100 KC-767A 

aircraft pending final approval, the effort is planned for completion in 2011 

or later. Moreover, this plan does not lead to replacement of any of the 417 

KC-135R aircraft, a process that could last another 20 to 30 years. As a 

result, U.S. combat and mobility air forces are likely to continue to rely on 

some KC-135R aircraft for aerial refueling through at least the 2020 to 2030 

time frame. 

Since 1991, U.S. airpower has been used in combat in the Middle East, the 

Balkans, Afghanistan, and in the United States on homeland defense 

missions. Aerial refueling has played a vital supporting role in these 

operations due to the long distances between bases in the United States 

and elsewhere and the combat theaters, the distances within the theaters 

between bases and operating areas; the need to keep combat aircraft aloft 

for extended periods of time or maintain operations around the clock; and 

the relatively short operating ranges of many combat and support aircraft. 

Nearly every mission flown by combat and support aircraft during these 

conflicts required at least one, and often multiple refuelings from 

U.S. refueling aircraft. Table 1 depicts aerial refueling activity in the last 

four major conflicts. 

 7

 We did not review aerial refueling mission accomplishment for missions prior to 1991; 

however, we are not aware of any shortcomings prior to that date. 

Current Force Has 

Met Refueling Needs 

but at Increasing Cost 

and Effort 

DOD’s Aerial Refueling 

Force Has Met Refueling 

Fleet Needs in Combat and 

Peacetime Operations 
Page 10 GAO-04-349 Military Aircraft 

Table 1: Air Force Aerial Refueling Statistics for Major Conflicts Since 1991 

 Iraq (1991) Kosovo (1999) Afghanistan 2001-02 Iraq 2003

Number of refueling aircraft 306 175 80 185

Sorties 16,865 5,215 15,468 6,193

Flight hours 66,238 52,390 115,417 Not available

Average sortie length (hrs) 3.9 10.0 7.5 Not available

Receiver aircraft 51,696 23,095 50,585 28,899

Fuel off-loaded (lbs) 800.7M 253.8M 1,166M 376.4M

Avg. fuel per sortie (lbs) 47.5K 48.7K 75.4K 60.8K

Source: GAO analysis of Air Force data. 

According to the Air Force, since the terrorist attacks of 

September 11, 2001, the refueling fleet has been increasingly stressed due 

to operational requirements. Table 2 depicts the percentages of the KC-135 

fleet that flew within various ranges of flight hours each year from fiscal 

years 1996 through 2002. 

Table 2: Distribution of Flying Hours for the KC-135 Fleet (Fiscal Years 1996-2002) 

Percentage of KC-135 fleet 

Hours per aircraft 1996 1997 1998 1999 2000 2001 2002

0 3.1 4.2 4.2 5.8 8.3 7.1 4.2

1-99 3.4 5.3 5.4 9.8 11.6 11.3 7.3

100-199 11.9 8.3 8.3 9.3 11.3 9.6 9.1

200-299 16.3 13.4 16.7 18.1 20.1 18.7 12.4

300-399 28.6 34.2 28.1 21.6 22.0 22.0 15.8

400-499 23.1 20.5 21.6 12.9 13.6 18.5 19.5

500-599 7.6 9.4 10.3 7.4 7.8 8.4 15.5

600-699 4.9 4.2 4.2 6.0 3.6 3.5 8.7

700-799 1.1 0.5 0.9 4.7 0.9 0.5 3.5

800-899 0 0 0 2.0 0.7 0.4 1.5

900-999 0 0 0.2 1.1 0 0 1.5

>1000 0 0 0 1.3 0 0 1.3

Source: GAO analysis. 

The cumulative lifetime fleetwide average was about 16,000 hours per 

KC-135 aircraft at the time of our review, less than half of the projected 

limit of 36,000-39,000 hours per aircraft, according to Air Force data. In 

2001, the Air Force projected that the fatigue life for nearly all of the 
Page 11 GAO-04-349 Military Aircraft 

KC-135 aircraft should permit their usage until 2040. However, since 2001, 

the Air Force has become concerned that unknown future problems could 

arise and lead to the grounding of the KC-135 fleet, thereby undermining 

refueling capability. 

While the KC-135 fleet was delivered between 1957 and 1965, significant 

portions of the aircraft have been upgraded or modified since. Thus, while 

the aircraft are considered old, significant improvements have been 

incorporated into the aircraft since, including capability-enhancing 

modifications and replacement of major structural components. For 

example, between 1975 and 1988, the Air Force replaced about 

1,500 square feet of the aluminum skin on the underside of the wings of 

most KC-135 aircraft with an improved aluminum alloy that was less 

susceptible to fatigue. Engine strut fittings were also replaced. 

In addition to such specific large-scale, fleetwide upgrade programs, most 

aircraft have had some other major structural components replaced as 

necessary, and some major components have been replaced on all aircraft. 

Examples of some of these major structural repairs include replacement of 

segments of fuselage skins, floor beams, fuselage bulkheads, and upper 

wing skins. Figure 3 shows replacement of fuselage skin underway on a 

KC-135 aircraft. 

KC-135 Aircraft Has 

Undergone Significant 

Improvements to Remain 

Combat Ready 
Page 12 GAO-04-349 Military Aircraft 

Figure 3: Removal and Replacement of KC-135 Fuselage Skin 

Source: U.S. Air Force.

Skins installed

Skins removed
Page 13 GAO-04-349 Military Aircraft 

As components such as these are replaced, the use of new and improved 

materials, fabrication, and corrosion prevention techniques are being used 

to prevent corrosion and allow for increased service life of the parts. 

KC-135 operations and support costs have risen significantly since 1996. 

As shown in table 3, the actual average cost per flying hour, adjusted to 

constant 2002 dollars, increased from $8,476 per hour in 1996 to $10,955 

per hour in 2002, an increase of 29 percent. 

Table 3: KC-135 Operating and Support Costs (Fiscal Years 1996-2002) 

Constant fiscal year 2002 dollars in millions 

Cost category 1996 1997 1998 1999 2000 2001 2002

Mission personnel $693.6 $671.3 $641.1 $792.9 $780.2 $793.0 $778.2

Unit level consumption 475.4 473.9 514.8 525.7 388.1 485.0 633.8

Depot maintenance total 292.0 306.5 417.8 460.8 390.2 423.9 647.3

Contractor support total 6.0 4.6 8.3 10.8 5.8 13.3 4.2

Sustaining support total 30.1 18.8 23.1 22.9 24.5 24.5 38.4

Indirect support total 111.6 134.7 130.9 220.2 211.9 211.6 298.7

Total 1,608.7 1,609.8 1,736.0 2,033.3 1,800.7 1,951.3 2,400.6

 

Annual flying hoursa 189,827 188,579 189,236 195,851 157,786 165,574 219,136

Cost per flying hour 8,476 8,536 9,173 10,382 11,412 11,785 10,955

Source: GAO analysis of Air Force data. 

a

Excludes hours for four KC-135D aircraft that are scheduled for retirement in fiscal year 2005. 

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. 

To maintain serviceability, each KC-135 aircraft periodically undergoes 

programmed depot maintenance. During this maintenance, crews inspect 

the aircraft, repair or replace structural components and systems, make 

modifications, and strip and reapply paint. Figure 4 shows the location and 

damage to a component of a refueling aircraft’s frame that was discovered 

during program depot maintenance. The part was replaced. 

KC-135 Operating and 

Support Costs Have 

Increased Significantly 

KC-135 Depot Maintenance 

Trends Change 
Page 14 GAO-04-349 Military Aircraft 

Figure 4: Example of a Cracked Frame Component That Was Replaced During Programmed Depot Maintenance 

Source: U.S. Air Force.

Installed frame

(As seen from wheel well)

Frame removed

Cracked flange
Page 15 GAO-04-349 Military Aircraft 

Most KC-135 aircraft are scheduled for depot maintenance every 5 years, 

although aircraft based in locations subject to humid air and/or a salt air 

environment are generally scheduled every 4 years.8

Between mid-1994 and mid-1998, an average of about 100 KC-135 aircraft 

were at a depot at any given time. However, by mid-2000, that number had 

risen to 166 aircraft, about 30 percent of the fleet, due in part to 

modernization programs and the need for more extensive maintenance 

attributed to the aircraft aging. As shown in figure 5, the average number 

of days that each KC-135 spent in depot maintenance, known as “depot 

flow days,” rose sharply during the 1990s but declined significantly in 

fiscal year 2000, due to a variety of short-term initiatives. 

 8

 KC-135 depot maintenance is performed at the Oklahoma City Air Logistics Center at 

Tinker Air Force Base, Oklahoma; the Boeing Aircraft Support Center in San Antonio, 

Texas; and at PEMCO Inc. in Birmingham, Alabama. 
Page 16 GAO-04-349 Military Aircraft 

Figure 5: Trend in the Number of Depot Flow Days for Programmed Depot 

Maintenance Per KC-135 Aircraft (Fiscal Years 1991-2000) 

Between 1991 and 2000, the Air Force doubled the basic depot 

maintenance package, accounting for a significant portion of the increased 

depot flow days. The change increased maintenance time from 16,000 

hours to 32,000 hours9

 on average per aircraft. Moreover, other factors also 

increased maintenance time including: 

• the removal and replacement of major portions of wiring systems 

(5,200 hours per plane); 

• one-time structural changes to prevent corrosion (2,100 hours per 

plane); and 

• unplanned major structural repairs, including replacement of floor 

beams, fuselage bulkheads, and fuselage skins (increased by 6,000 

hours per plane). 

Depot flow days began to decline in fiscal year 1999 but recognizing the 

need to try to further reduce depot flow days and despite the doubling of 

 9

 These hours are calculated by tallying the total number of hours that each maintainer 

worked on an aircraft. 

Depot flow days

Years

Source: Air Force.

0

50

100

150

200

250

300

350

400

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
Page 17 GAO-04-349 Military Aircraft 

the maintenance package, in 2001, the Air Force made improvements to 

depot operations. These changes included: 

• deferring maintenance if warranted based on an inspection of the 

aircraft; 

• increasing the number of maintenance personnel; 

• moving engineers to production to shorten decision-making time on 

whether to remove, repair, or replace a damaged or worn aircraft 

component; 

• and increasing second shift operations. 

As a result, the number of aircraft in the depot decreased from 176 to 89 

between September 2000 and September 2002 with no known degradation 

in aircraft safety and readiness. The Air Force expects the number of 

KC-135s in depot maintenance to continue to decline to 73 aircraft in fiscal 

year 2005, followed by a gradual increase to 89 aircraft in fiscal year 2020. 

The Air Force plans to embark on a program to replace the KC-135 fleet 

without a current study to identify the number or type of aircraft needed 

for the future refueling mission. The most recent study is Tanker 

Requirements Study-05. However, it specifies the number of refueling 

aircraft needed for the outdated two-major-theater-war strategy, which 

was replaced by the 2001 Quadrennial Defense Review. Moreover, 

refueling requirements could change still more due to force transformation 

initiatives, projected changes in operational concepts, the advent of new 

technologies such as unmanned aerial vehicles, and force structure 

changes. Finally, the Air Force also has not conducted a recommended 

analysis of alternatives to identify the approach best suited to meeting 

refueling mission requirements prior to committing to a specific approach. 

Consequently, the Air Force may embark on an expensive program to 

invest in new aircraft without knowing how many it needs and may miss 

an opportunity to meet its needs using the most cost-effective approach. 

The KC-135 aircraft design and fleet size has evolved from 

post-World War II requirements to that needed to carry out the 

U.S. strategy of containment of the former Soviet Union. The Air Force 

acquired more than 700 KC-135 aircraft between 1957 and 1965, principally 

to refuel bombers that would have carried out the strategic nuclear war 

plan. Thus, the KC-135 aircraft was equipped with a boom to provide high 

refueling rates that strategic bombers needed. In that role, the refueling 

aircraft spent 30 percent of their time on nuclear alert ready for takeoff 

Air Force’s Aerial 

Refueling 

Requirements Are 

Outdated 

Current Refueling Force Is 

a Cold War Legacy 
Page 18 GAO-04-349 Military Aircraft 

but were not actually flown much. In the post-Cold War era, the aerial 

refueling aircraft mission has changed to the support of global operations 

of all strike and cargo aircraft, but the KC-135 fleet was reduced to 538 

aircraft from over 700. 

The most recent study effort addressing Air Force aerial refueling 

requirements is Tanker Requirements Study-05, which was issued in 

February 2001. According to Air Force officials, the purpose of the study 

was to determine the number of tanker aircraft and aircrews needed to 

support the National Military Strategy of conducting two nearly 

simultaneous major theater wars in Korea and in Southwest Asia. The 

study also included the refueling requirements to support the strategic 

nuclear plan, certain special operations, and smaller-scale contingencies. 

The study identified shortages of both aircrews and aircraft in certain 

scenarios. 

Tanker Requirements Study-05 concluded that up to 1,033 aircrews were 

needed, depending on the scenario. When we applied the KC-10 and 

KC-135 crew ratios to the number of aircraft in the inventory, we derived a 

total of over 840 aircrews, a shortage of about 190 crews. The KC-10 crew 

ratio is 2.0 crews per active duty aircraft and 1.5 crews per reserve 

component aircraft while the KC-135 crew ratio is 1.36 crews per active 

duty aircraft and 1.27 crews per reserve component aircraft. However, 

even this level was insufficient in Operation Desert Storm when the Air 

Force needed 1.5 crews per KC-135 aircraft, and in Operation Allied Force 

when it needed 1.8 crews per KC-135 aircraft. To meet the immediate 

mission requirements of these operations, the Air Force deployed more 

crews from their home bases without their aircraft. While this permitted 

the Air Force to meet the immediate needs of the specific operation, it also 

significantly undermined the refueling capability that would normally be 

available for other concurrent contingencies. 

Tanker Requirements Study-0510 also concluded that, depending on the 

scenario, the Air Force needed up to 607 KC-135R-equivalent11 aircraft to 

 10 We did not evaluate the validity of the study’s analysis. 

Most Recent Study 

Reflects Now Outdated 

Two-Major-Theater-War 

Strategy 
Page 19 GAO-04-349 Military Aircraft 

meet aerial refueling requirements in 2005 and uses such equivalencies to 

evaluate its refueling capacity. When we applied the equivalencies to the 

fleet in March 2004, acknowledging that some aircraft will not be available 

due to aircraft needed for training (24) and aircraft in depot maintenance 

(98), the Air Force had the equivalent of 507 KC-135R available aircraft, as 

shown in table 4. 

Table 4: Number of Air Force Aerial Refueling Aircraft in the Fleet Expressed as KC-135R Aircraft Equivalents 

Aircraft 

Number in 

the fleet in 

March 2004 

Used in 

traininga

In depot 

maintenancea

Number in the 

fleet available

Equivalency 

factor 

Number in fleet in 

2004 as an 

equivalency 

of the KC-135R

KC-135E 121 20 101 0.84 85

KC-135R 417 24 70 323 1.00 323

KC-10 59 8 51 1.95 99

Total 597 24 98 475 na 507

Source: Air Force. 

a

Estimated number of aircraft expected to be unavailable for operations in 2004. As we pointed out 

previously in this report, the Air Force expects the number of KC-135 aircraft in depot to decrease to 

73 by fiscal year 2005 and gradually increase to 89 in fiscal year 2020. Thus between 335 and 351 

KC-135 aircraft could be available for operations between 2005 and 2020. 

Major changes in U.S. national security strategy and changes in 

operational concepts could have a significant effect on the type and 

number of aerial refueling aircraft needed. 

Prior to 2001, U.S. national security strategy was based on the longstanding two major theater war threat-based model, which focused on 

specific adversaries and geographic locations. Tanker Requirements 

Study-05 is based on this approach. In 2001, the Quadrennial Defense 

Review shifted defense planning to a “capabilities-based” construct based 

 11“Tanker equivalents” reduces the differing capabilities of various refueling aircraft to a 

common standard. Tanker Requirements Study-05 established the range and offload 

capability of the KC-135R as the standard, thus its equivalency is one. A KC-135E can 

offload less fuel than can a KC-135R because the E model carries less fuel and its engines 

are not as fuel-efficient. Therefore, its equivalency to a KC-135R is 0.84 to 1.00. The KC-10, 

on the other hand, has a greater fuel capacity than the KC-135R. Thus, its equivalency is 

1.95 to 1.00. 

New Strategies and 

Changing Operational 

Concepts Could Affect 

Aerial Refueling 

Requirements 

2001 Quadrennial Defense 

Review Promulgated New 

Defense Strategy 
Page 20 GAO-04-349 Military Aircraft 

on the assumption that the United States cannot know which specific 

nation or group may pose a future threat, although defense planners can 

anticipate the range of capabilities an adversary might employ. 

Under the strategy articulated in the Quadrennial Defense Review, U.S. 

forces must: 

• defend the U.S. domestic population, territory, and critical defenserelated infrastructure against attacks from outside U.S. borders; 

• deter aggression and coercion by maintaining regionally tailored forces 

forward stationed and deployed in Europe, Northeast Asia, the East 

Asian littoral, and the Middle East/Southwest Asia; 

• swiftly defeat aggression against U.S. allies and friends in two 

overlapping major conflicts; and 

• decisively defeat the adversary in one of two major conflicts by 

imposing U.S. will and removing any future threat from that adversary. 

The revised strategy significantly broadens the scope of potential theaters 

of operations. Moreover, Air Force officials believe that the Quadrennial 

Defense Review approach represents a significant increase in potential 

mission requirements and carries with it a concomitant increase in 

refueling requirements. At the same time, increasing domestic operations 

in defense of the U.S. homeland may also impose substantial aerial 

refueling requirements not previously contemplated. As shown in table 5, 

in addition to changes in U.S. national security strategy, changes in 

(1) overseas basing rights, (2) operational concepts, (3) the extent of use 

of precision-guided munitions, (4) joint operations, and (5) technology 

could also change refueling requirements. 
Page 21 GAO-04-349 Military Aircraft 

Table 5: Changes to National Strategies and Operational Concepts That Could Lead to Changed Aerial Refueling 

Requirements 

Change Discussion 

Changes in strategy If changes to U.S. national security strategies occur, including the 2005 Quadrennial Defense 

Review, refueling requirements could also change. For example, “anti-access environments” 

may exist whereby both the tanker and receiver aircraft would be required to fly longer 

distances, causing the tanker to have less fuel to offload and the receiver aircraft to require more 

fuel. 

Overseas basing The potential loss of overseas basing rights without a concomitant increase in basing rights 

elsewhere or contemplated overseas force realignments could force U.S. combat and support 

aircraft to operate from bases at greater distances from theaters of operations and consequently 

require additional aerial refueling to meet combat and support mission requirements. 

Operational concepts Refueling requirements could change if individual aircraft in the new refueling fleet can remain 

longer at aerial refueling rendezvous points and themselves be aerially refueled. 

Precision-guided munitions Increased reliance on precision-guided munitions could change refueling requirements if 

standoff distances increase for combat aircraft, thereby decreasing distances from the 

operational base to the munitions’ launch location, and if precision munitions’ success rate 

increases sufficiently to reduce the number of sorties needed to bring the same effects on target.

Mixed receivers on joint operations The Air Force uses one type of refueling system known as a “boom and receptacle,” while Navy, 

Marine Corps, and many allied aircraft use another system, known as “hose and drogue.” 

Consequently, increasing reliance on joint operations leads to increased requirements for both 

boom and receptacle, and hose and drogue off load capabilities. If the refueling fleet can operate 

either type of offload mechanism on a single mission, refueling requirements could be still 

different. 

Emerging technologies Some emerging technologies such as unmanned aerial vehicles have much longer ranges than 

manned systems and may lead to changed refueling requirements. 

Source: GAO analysis. 

Other aircraft acquisition and modification programs may also affect 

future aerial refueling requirements. For example, Air Force officials 

believe that newer aircraft will be increasingly fuel efficient, possibly 

increasing their ranges and potentially reducing the number of refueling 

aircraft needed. In its 2003 report on re-engining the B-52 bomber fleet, the 

Defense Science Board examined the effect of more fuel-efficient engines 

on missions flown from Diego Garcia during Operation Enduring 

Freedom. Assuming that more efficient engines would increase the B-52s 

range by at least 25 percent, the Board found that the Air Force could 

reduce the size of the refueling fleet on Diego Garcia by one-third.12

 12 Department of Defense, Office of the Under Secretary of Defense for Acquisition, 

Technology and Logistics; Defense Science Board Task Force on B-52H Re-Engining

(Washington, D.C.: Dec. 2002). 

Other Factors Could Impact 

Requirements 
Page 22 GAO-04-349 Military Aircraft 

In addition, the Air Force may be expected to refuel fewer aircraft in the 

future potentially leading to a reduction in refueling aircraft requirements. 

For example, in its fiscal year 2004 budget submission, the Navy proposed 

a new Navy-Marine Corps Tactical Air Integration plan that is to more fully 

integrate the Navy and Marine Corps strike fighter forces between fiscal 

years 2003 and 2012. If implemented, Navy and Marine Corps strike fighter 

forces would be reduced from 872 to 562 aircraft, significantly reducing 

the number of aircraft needing aerial refueling. 

Initially, the Air Force plans to begin replacing its KC-135E aircraft, about 

130 planes, with 100 new KC-767A aircraft. The KC-767A, like most 

modern aircraft, will have advantages and capabilities not found on the 

KC-135s. In theory, these capabilities permit recapitalization of the 

refueling fleet with fewer but more efficient aircraft without degrading 

refueling capability. These capabilities could be added to new aircraft 

during construction or during refurbishment and conversion of used 

aircraft. 

• New aircraft can be equipped with engines that are considerably more 

powerful, yet more fuel efficient, maintainable, and less costly than 

those powering the KC-135Es. This enables larger aircraft to operate 

from shorter runways and to carry a greater payload (fuel, cargo, 

and/or passengers) longer distances than the KC-135R aircraft. This 

would allow new aircraft with characteristics similar to the KC-767A, to 

operate from four times as many runways and offload up to 20 percent 

more fuel than the KC-135E aircraft. 

• Refueling aircraft that are equipped to refuel both hose and drogue and 

boom and receptacle-type receiver aircraft on the same flight would 

enhance joint operations because a single refueling aircraft could 

refuel both Air Force and Navy aircraft without first landing and 

changing equipment or requiring two differently equipped aircraft to 

operate simultaneously. All of the KC-10 and 20 of the KC-135 refueling 

aircraft currently have this capability. 

• Refueling aircraft that can be aerially refueled themselves serve as 

force multipliers in the sense that they can remain airborne for much 

longer missions than the KC-135s and potentially support many more 

receiver aircraft. 

• Refueling aircraft that are equipped with wing-mounted refueling pods 

could refuel two Navy-allied receiver aircraft simultaneously. 

Greater Efficiencies of a 

Modern Refueling Aircraft 

Could Lead to Reduced 

Requirements 
Page 23 GAO-04-349 Military Aircraft 

• Refueling aircraft derived from commercial aircraft designs can be 

maintained according to commercial maintenance practices, which 

generally results in the aircraft spending less time in maintenance at 

any given time and consequently, being available for missions more 

often than the KC-135 aircraft. 

The national security strategy and defense planning guidance have 

changed considerably since Tanker Requirements Study 05 was 

completed. In addition, DOD Instruction 5000.2,13 which governs defense 

acquisition programs, identifies the basic process acquisition programs 

should follow, beginning with and based upon the overarching national 

security strategy, any existing national military strategies, and joint 

concepts of operations. Generally, a series of analyses should be 

conducted to identify: what is needed to achieve military objectives; 

current capabilities; gaps or shortcomings; and potential solutions. 

However, at the time of our work, DOD did not plan to conduct a new 

requirements study or replace Tanker Requirements Study 05. The 

guidance also recommends that DOD conduct an analysis of alternatives 

to evaluate the operational effectiveness, operational suitability, and 

estimated costs of alternative approaches to meet a mission capability. 

The analysis assesses the advantages and disadvantages of alternatives 

being considered to satisfy capabilities, including the sensitivity of each 

alternative to possible changes in key assumptions or variables. 

The Air Force did not comprehensively reassess aerial refueling 

requirements following the most recent Quadrennial Defense Review, nor 

did it conduct a comprehensive analysis of alternatives before it proposed 

to lease 100 KC-767A aerial refueling aircraft in 2003. Consequently, as a 

result of congressional concerns about this matter, the National Defense 

Authorization Act for Fiscal Year 2004 required that DOD complete an 

analysis of alternatives by March 2004. DOD issued a memorandum dated 

February 24, 2004, containing a preliminary report and outlining the 

framework and parameters for the Air Force overview study of various 

options for replacing its aging fleet of KC-135 refueling aircraft. In 

addition, DOD has contracted for a study of the material condition of its 

 13 DOD Instruction 5000.2, “Operation of the Defense Acquisition System,” May 12, 2003, 

implements DOD Directive 5000.1, “The Defense Acquisition System,” dated May 12, 2003. 

One of the stated purposes of 5000.2 is to “establish a simplified and flexible management 

framework for translating...approved mission needs and requirements, into stable, 

affordable, and well-managed acquisition programs that include weapon systems.” 

Updated requirements 

study and analysis of 

alternatives were not 

planned at the time of our 

work 
Page 24 GAO-04-349 Military Aircraft 

fleet of KC-135 aerial refueling aircraft with a report due by September 

2004. Finally, to fully comply with the congressional reporting requirement 

and the DOD February 2004 memorandum, the Air Force plans to issue an 

analysis of alternatives in August 2005. 

Replacing over 500 KC-135s will likely cost tens of billions of dollars, and 

the time period over which this will be done could last several decades, a 

period in which aircraft technology and aerial refueling needs, as well as 

U.S. national security and military strategies and operational concepts 

could change significantly. Just as conditions in the first decade of the 21st 

century are dramatically different than they were in the mid-1950s when 

the KC-135s were introduced, so too will conditions be far different 30 to 

40 years from now. As the Air Force begins to modernize its aerial 

refueling fleet, it has three alternatives available that have either been used 

previously or were being tested at the time of our report. The most 

obvious alternative is to acquire one or more variants of new commercial 

aircraft and convert them to refueling aircraft. A second option is to 

acquire used commercial aircraft and convert them into refueling aircraft. 

Thirdly, the Air Force could contract for a portion of its aerial refueling 

needs as a service. The most cost-effective solution may be a combination 

of these or other options that would be closely examined in a 

comprehensive analysis of alternatives, although the Air Force’s analysis 

of alternatives was not planned to review the option of contractorprovided aerial refueling. 

Three Options Exist 

to Meeting the Air 

Force’s Future Aerial 

Refueling 

Requirements 
Page 25 GAO-04-349 Military Aircraft 

The Air Force could acquire one or more variants of new production 

aircraft and convert them to refueling aircraft either through purchase, 

lease, or a combination of the two.14 These new aircraft could consist of a 

mixed force comprised of small, medium, and large aircraft suitable for 

supporting a wide range of refueling operations. For example, in some 

instances, U.S. airpower may be needed in parts of the world where there 

are few suitable overseas airfields from which to operate large refueling 

aircraft. In such cases, smaller tactical refueling aircraft capable of 

operating from short, unimproved airfields close to the battlefield may be 

desirable. In other instances, U.S. aircraft may be denied access to 

airfields close to the battlefield, requiring combat aircraft to fly extremely 

long distances with multiple aerial refuelings and large amounts of fuel. In 

these instances, large strategic refueling aircraft capable of offloading 

large amounts of fuel may be desirable. Regardless of the ultimate aircraft 

mix, the overall cost to procure these planes could be extremely 

expensive. If the Air Force could buy new refueling aircraft at the 

$131 million price negotiated with the Boeing Company in 2003, it would 

spend about $71 billion (in 2003 dollars), excluding support and other 

costs, to replace all of the KC-135 fleet on a one-for-one aircraft basis. On 

the other hand, if the Air Force leased some of these aircraft over a long 

period of time—10 years for example—its cost per aircraft could be about 

$80 million to $125 million.15 While purchasing costs less than leasing if the 

aircraft is retained for its full service life of 20 to 30 years, leasing could 

have merit in some instances—for example to temporarily fill a known 

capability gap before a significantly improved technologically-advanced 

new aircraft can be produced. 

Currently, the aircraft most discussed as the initial replacement for some 

of the KC-135 fleet is the Boeing KC-767A. Section 8159 of the Department 

of Defense Appropriations Act for Fiscal Year 200216 authorized the Air 

 14 In 1996, we recommended that the Air Force consider a multi-role aircraft that could 

conduct either aerial refueling or airlift operations as a replacement for the KC-135. See 

U.S. General Accounting Office, U.S. Combat Air Power: Aging Refueling Aircraft Are 

Costly to Maintain and Operate, GAO/NSIAD-96-160 (Washington, D.C.: Aug. 8, 1996). 

15 Based on a lease rate for wide-body aircraft of one-half to eight-tenths of 1 percent per 

month of the estimated purchase price, multiplied by duration of the lease. This formula 

was presented by an expert in commercial leasing at a July 23, 2003, hearing held by the 

Committee on Armed Services, House of Representatives. 

16 Department of Defense and Emergency Supplemental Appropriations for Recovery from 

and Response to Terrorist Attacks on the United States Act, 2002, Pub. L. No. 107-117, 

§ 8159, 115 Stat. 2230, 2284-85 (2002). 

Acquiring New Aircraft 
Page 26 GAO-04-349 Military Aircraft 

Force to lease up to 100 aerial refueling aircraft, which the Air Force tried 

to do in 2003 when it sought congressional approval of its leasing plan. 

Subsequent to the hearings and in the National Defense Authorization Act 

for Fiscal Year 2004, Congress amended the original lease provision and 

authorized the Air Force to lease 20 new KC-767A aircraft and purchase 

80.17 The KC-767A has about the same fuel capacity as the KC-135R and is 

larger and heavier, but more fuel-efficient. Another current aerial refueling 

aircraft candidate is the Airbus A330 aircraft. The A330 is considerably 

larger than the KC-767A and has about 20 percent greater fuel capacity. It 

was being considered as the replacement refueling aircraft in the United 

Kingdom at the time of this report. Another Airbus model, the A310 is 

being operated with five international air forces, with the first aerial 

refueling version expected to be operational with the German Air Force in 

the first half of this year. In addition, two other aircraft are being 

developed that could potentially serve as future refuelers. Airbus is 

developing the A380, which is somewhat larger than the Boeing 747 and is 

expected to enter passenger service in 2006. Airbus claims the A380 will 

burn 13 percent less fuel but carry about 35 percent more passengers. 

Boeing has begun developing the 7E7, which will be closer in size to the 

A330. Boeing claims the 7E7 will be 20 percent more efficient than current 

aircraft. 

Also, future unmanned aerial refueling vehicles may be another acquisition 

option to be considered by the Air Force and is denoted as a possible 

option to study in DOD’s February 2004 guidance to the Air Force. The 

Unmanned Aerial Vehicles Roadmap released by DOD in March 2003 

suggests the possibility of such unmanned aerial refueling vehicles being 

in the Air Force’s inventory in the 2015-2020 time period.18 The 

development and deployment of such vehicles would permit their 

remaining at an aerial refueling rendezvous point for long durations 

without entering a combat zone. In addition, such a collection of 

unmanned aerial refueling vehicles may be smaller in size than the aerial 

refueling aircraft now being considered and may better meet the needs of 

the Air Force in certain unique operations. 

 17 National Defense Authorization Act for Fiscal Year 2004, Pub.L. No. 108-136, § 135, 

117 Stat. 1392, 1413-14 (2003). 

18 U.S. Department of Defense, Unmanned Aerial Vehicles Roadmap, 2002-2027 

(Washington, D.C.: December 2002). 
Page 27 GAO-04-349 Military Aircraft 

The Air Force could augment its refueling fleet by acquiring some used 

aircraft from among the over 1,500 commercial airliners in storage at the 

time of our report.19 Under this approach, the Air Force would convert 

them to aerial refueling aircraft. Some of these aircraft are relatively new 

or have not been used extensively, while others are older and have been 

used extensively. However, with extensive refurbishment and conversion 

into a refueling and cargo-capable aircraft, these aircraft could be suitable, 

given the relatively few hours refueling aircraft fly each year when 

compared to commercial aircraft. Possible limitations are that it is not 

known whether the owners would sell the aircraft, the cost to convert 

them could be high, and introduction of differing aircraft types into the 

fleet could complicate maintenance and logistics because different spare 

parts would need to be stockpiled and maintenance crews would need 

different types of training. 

Under this concept the Air Force would maintain a core aerial refueling 

capability and augment it with contractor-provided refueling services that 

could be activated on short notice—an aerial refueling Civil Reserve Air 

Fleet—to meet additional anticipated aerial refueling demands that may 

exceed its own capacity. We envision that this approach could be similar 

to the Civil Reserve Air Fleet program in which commercial airlines agree 

in advance to make some of their aircraft and crews available to DOD 

when needed to transport troops to a theater of operations in wartime. In 

addition, contractor refuelers could be used to meet some of the noncombat aerial refueling demands such as proficiency training for receiver 

aircraft aircrews, supporting the deployment of aircraft during periodic Air 

Force Air Expeditionary Force rotations, and other planned aircraft 

movements. Currently, these types of support missions can add a 

considerable amount of additional time that active duty and reserve 

component refueling aircrews must spend away from their home bases. 

Before joining the program’s pool of eligible aircraft, the aircraft would be 

structurally modified, and basic aerial refueling equipment including 

additional fuel tanks, lines, and pumps, would be installed, most likely at 

government expense. Some of this equipment, such as external refueling 

booms and pods, and militarily-unique avionics could be designed so that 

 19 Speednews.com, a commercial aviation Web site, reported that there were 475 wide-body 

jets in storage in December 2003 and 1,147 narrow-body jets. Of the wide-body aircraft, 

there were 119 B-747s, 71 B-767s, 81 DC-10s, and 26 MD-11s. 

Acquire Used Aircraft 

Obtain Refueling Services 

from a Contractor 
Page 28 GAO-04-349 Military Aircraft 

it can be quickly added or removed depending on whether the aircraft is to 

be operated in a military or civilian capacity. The aircraft owners would 

most likely operate these aircraft for commercial airfreight business when 

not needed for aerial refueling. 

Contractor-owned aircraft would not necessarily have to be used in the 

combat theater, but could nevertheless provide significant refueling 

support, and free up military refueling aircraft to be used in combat areas. 

For example, these aircraft could be used to provide the “air bridge” 

refueling to support the movement of fighters, bombers, and transport 

aircraft from home bases in the United States or elsewhere to the combat 

theater of operations but never enter the theater.20 DOD and the Air Force 

did not plan to include the option of contractor-provided aerial refueling in 

its analysis of alternatives, at the time of our review. 

The Navy is conducting a pilot program to examine the feasibility of using 

contractor-provided aerial refueling services to meet some of its aerial 

refueling needs. The Navy refueling aircraft is a Boeing 707, the same 

aircraft on which the Air Force’s current workhorse KC-135 is based. At 

times, Air Force refueling aircraft have not been available to support Navy 

training due to the lower priority placed on Navy training by the Air Force, 

and sometimes training plans changed on relatively short-notice; hence, 

the Navy sought alternatives and developed the pilot program. According 

to a Center for Naval Analyses study, the Navy’s contractor has enhanced 

aircraft carrier training. The study reported that having an aerial refueling 

aircraft controlled by and dedicated to the Navy provided flexibility during 

periods of high-operational tempo, and saved time and fuel as Navy 

aircraft flew coast to coast to conduct training. Moreover, Navy officials 

have stated that at least in the early stages of its pilot program, mission 

availability rates have been excellent for operations performed in the 

continental United States and in supporting training exercises in Puerto 

Rico. The presence of a large dedicated refueling aircraft during training 

has also enabled Navy aircraft to rely less on their own refuelingcapability, currently S-3B and F/A-18F fighter aircraft that can refuel other 

fighters, and allow those aircraft, especially the F/A-18D/Es to focus on 

their primary combat missions. While Navy officials expressed positive 

views about their experience to date with contractor-provided aerial 

refueling, they also said that landing privileges at military bases, peacetime 

 20 The Air Force used 100 refueling aircraft during Operations Desert Shield and Desert 

Storm to support the Atlantic and Pacific “air bridges.” 
Page 29 GAO-04-349 Military Aircraft 

and wartime communication requirements, reliability, and other issues 

would need to be worked out if this approach were used on a large scale. 

The Air Force is embarking on a program that could cost billions of dollars 

to replace the existing KC-135 fleet without knowing how many or what 

types of replacement aircraft it needs, because it does not have a current 

requirements study. Consequently, the Air Force could miss opportunities 

to meet its refueling needs in the most cost-effective manner; it does not 

have a roadmap to guide it as it makes investment decisions about tanker 

replacement. The Air Force could begin its tanker replacement program 

along the lines of the lease-buy program approved by Congress last year 

without such a roadmap, but we believe that long-term replacement 

decisions for the remainder of the tanker fleet should be based on a sound, 

comprehensive requirements study reflecting the most up-to-date analysis 

possible of the future environment. 

Also, at least three options exist for meeting DOD’s aerial refueling needs, 

but without a comprehensive analysis of alternatives, the Air Force would 

not know what option or combination of options are best suited to 

meeting the requirements. As a result, the Air Force would not have a 

sufficient basis on which to make its investment decision. Thus, we agree 

with the February 2004 DOD initiative for the Air Force to conduct an 

analysis of alternatives study for meeting the aerial refueling requirements. 

We believe, however, that the planned analysis of alternatives would be 

more effective and useful if it included all potential options, especially the 

possibility of meeting at least a portion of tanker needs through the use of 

contractor-provided refueling. 

To provide a current, comprehensive roadmap to guide long-term 

replacement of the current tanker fleet, we recommend that the Secretary 

of Defense conduct a new, validated requirements study to determine the 

current and projected aerial refueling requirements. 

We also recommend that the Secretary of Defense direct that the Air 

Force’s planned analysis of alternatives be a comprehensive study of all 

reasonable options, including using contractor-provided aerial refueling 

services to meet some portion of its aerial refueling needs. 

Conclusions 

Recommendations for 

Executive Action 
Page 30 GAO-04-349 Military Aircraft 

We received written comments on a draft of this report from the Director 

of Defense Systems in the Office of the Undersecretary of Defense for 

Acquisition, Technology, and Logistics. In its comments, DOD concurred 

with each of our recommendations. First, DOD indicated that a Mobility 

Capabilities Study was underway at the time of our report to determine 

aerial refueling requirements. Second, DOD indicated that the analysis of 

alternatives would include consideration of contractor-provided aerial 

refueling as a potential alternative. DOD’s comments are printed in their 

entirety in appendix II. 

In addition, DOD provided technical comments which we incorporated in 

our report where appropriate. 

We are sending copies of this report to other appropriate congressional 

committees, the Secretary of Defense, the Secretary of the Air Force, and 

the Director, Office of Management and Budget, and it will be available at 

no charge on GAO’s Web site at http://www.gao.gov. If you or your staff 

have any questions about this report, please contact me at (202) 512-4914. 

Key contributors to this report are listed in appendix III. 

Neal P. Curtin 

Director, Defense Capabilities 

 and Management 

Agency Comments 

and Our Evaluation 
Appendix I: Scope and Methodology 

Page 31 GAO-04-349 Military Aircraft 

Our objectives were to examine (1) the extent to which DOD’s current 

aerial refueling force has met aerial refueling needs, and the cost and 

effort associated with operating and sustaining the current aircraft fleet; 

(2) the most recent aerial refueling requirements; and (3) options to enable 

DOD to meet future aerial refueling requirements. 

To examine the extent to which DOD’s current aerial refueling force has 

met refueling needs, we conducted interviews with DOD and Air Force 

officials and obtained documents showing the services’ refueling needs in 

recent operations and the mission capable rates achieved of the current 

refueling fleet. In addition, to examine the cost and effort to operate and 

maintain the existing aerial refueling fleet, we interviewed officials and 

obtained documents from the Office of the Chief of Air Force Acquisition, 

Global Reach Program. We also visited the Air Force’s Air Mobility 

Command at Scott Air Force Base, Illinois, and the Air Force’s Oklahoma 

Air Logistics Center at Tinker Air Force Base and interviewed key aerial 

refueling aircraft operations, maintenance, and program analysis officials. 

At both locations, we reviewed cost and maintenance documents. We did 

not independently verify the reliability of the cost and maintenance data 

provided to us however, we discussed cost estimates with certain external 

organizations, including the Institute of Defense Analyses, the American 

Transport Association, and other organizations and determined the data 

that we had obtained was reasonable. We also reviewed testimony by 

DOD, Air Force, and other officials before a variety of congressional 

committees considering the proposed lease of 100 KC-767A aerial refueling 

aircraft. 

To examine the most recent aerial refueling requirements, we met with 

officials from the Office of the Secretary of the Air Force, and 

U.S. Transportation Command officials responsible for determining 

refueling requirements and operating costs and obtained key requirements 

documents including DOD Instruction 5000.2, “Operation of the Defense 

Acquisition System,” Chairman of the Joint Chiefs of Staff Instruction 

3170.01C, “Joint Capabilities Integration and Development System,” June 

24, 2003, and other documents showing the characteristics, missions, 

requirements, employment concepts, and costs of operation of the 

refueling aircraft. We also reviewed a briefing on Tanker Requirements 

Study-05 and the complete Mobility Requirements Study-05, and other Air 

Force briefings, and related documents. To gain a better perspective of air 

refueling operations and requirements, we discussed with appropriate Air 

Force and DOD officials the services’ policies, priorities, and procedures 

for using, modernizing, and maintaining their refueling aircraft inventory. 

Moreover, we obtained information documenting required KC-135 

Appendix I: Scope and Methodology 
Appendix I: Scope and Methodology 

Page 32 GAO-04-349 Military Aircraft 

maintenance and planned modifications to the aircraft. We also reviewed 

several studies and reports addressing various aerial refueling fleet topics, 

including those developed in recent major combat operations. We also 

reviewed a report from the Congressional Budget Office that estimates 

refueling aircraft maintenance and replacement costs. In addition, we 

discussed aerial refueling issues with representatives of several research 

organizations including the Institute of Defense Analyses and The Rand 

Corporation, and major military aircraft manufacturers including The 

Boeing Company and Lockheed-Martin. When analyzing the problems of 

maintaining aging aircraft, we concentrated on the Air Force’s KC-135 

aircraft because it makes up the bulk of the DOD’s aerial refueling 

inventory. 

Finally, to examine options to enable DOD to meet its aerial refueling 

requirements, we met with officials from the Office of the Secretary of 

Defense (Comptroller); Office of Air Force Acquisition, Global Reach 

Programs; the Air Force’s Air Logistics Center at Tinker Air Force Base; a 

contractor who was providing refueling services to the Navy at the time of 

our review; the Office of Management and Budget; the Air Transport 

Association; several major U.S. commercial airlines; and the United 

Kingdom’s Ministry of Defense, which was preparing to lease aerial 

refueling aircraft at the time of our review. We used our 1996 report on 

aging refueling aircraft and related accelerating operation and 

maintenance cost problems to suggest ways for DOD to consider 

recapitalizing its aerial refueling fleet. Moreover, we reviewed documents 

and briefings from many of these same organizations to identify options 

available to the Air Force and DOD to meet current and projected aerial 

refueling requirements. 

We performed our work from December 2001 through April 2004 in 

accordance with generally accepted government auditing standards. 
Appendix II: Comments from the Department 

of Defense 

 Page 33 GAO-04-349 Military Aircraft 

Appendix II: Comments from the Department 

of Defense 
Appendix II: Comments from the Department 

of Defense 

 Page 34 GAO-04-349 Military Aircraft 
Appendix III: GAO Contact and Staff 

Acknowledgments 

Page 35 GAO-04-349 Military Aircraft 

Brian J. Lepore (202) 512-4523 

In addition to the person named above, William C. Meredith; Kenneth W. 

Newell; Joseph J. Faley; Tim F. Stone; Fred S. Harrison; Norman L. Jessup, 

Jr.; James K. Mahaffey; Ann M. Dubois; Charles Perdue; and Kenneth E. 

Patton also made major contributions to this report. 

Appendix III: GAO Contact and Staff 

Acknowledgments 

Contact 

Acknowledgments 
Related GAO Products 

Page 36 GAO-04-349 Military Aircraft 

Military Aircraft: Observations on DOD’s Aerial Refueling Aircraft 

Acquisition Options. GAO-04-169R. Washington, D.C.: October 14, 2003. 

Military Aircraft: Institute for Defense Analysis Purchase Price 

Estimate for the Air Force’s Aerial Refueling Aircraft Leasing Proposal. 

GAO-04-164R. Washington, D.C.: October 14, 2003. 

Military Aircraft: Observations on the Proposed Lease of Aerial 

Refueling Aircraft by the Air Force. GAO-03-923T. Washington, D.C.: 

September 4, 2003. 

Military Aircraft: Observations on the Air Force Plan to Lease Aerial 

Refueling Aircraft. GAO-03-1143T. Washington, D.C.: September 3, 2003. 

Military Aircraft: Considerations in Reviewing the Air Force Proposal 

to Lease Aerial Refueling Aircraft. GAO-03-1048T. Washington, D.C.: July 

23, 2003. 

Military Aircraft: Information on Air Force Aerial Refueling Tankers. 

GAO-03-938T. Washington, D.C.: June 24, 2003. 

Air Force Aircraft: Preliminary Information on Air Force Tanker 

Leasing. GAO-02-724R. Washington, D.C.: May 15, 2002. 

U.S. Combat Air Power: Aging Refueling Aircraft Are Costly to Maintain 

and Operate. GAO/NSIAD-96-160. Washington, D.C.: August 8, 1996. 

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