GAO

United States General Accounting Office

Report to the Chairman, Subcommittee 

on Military Readiness, Committee on 

Armed Services, House of 

Representatives

June 2000 MILITARY 

READINESS

Air Transport 

Capability Falls Short 

of Requirements

GAO/NSIAD-00-135

Page 1 GAO/NSIAD-00-135 Military Readiness

Contents

Letter 5

Appendixes Appendix I: Airlift and Refueling Aircraft 22

Appendix II: Current Airlift and Aerial Refueling Capability 27

Appendix III: Aging of the Mobility Aircraft Contributes to Lower 

Mission Capable Rates 36

Appendix IV: Not Mission Capable for Supply and Cannibalization 

Rates Generally Exceed Air Mobility Command 

Standards 42

Appendix V: Scope and Methodology 49

Appendix VI: Comments From the Department of Defense 51

Appendix VII: GAO Contacts and Staff Acknowledgments 60

Tables Table 1: Airlift and Aerial Refueling Shortfall Based on Average 

Mission Capable Rates 10

Table 2: Air Mobility Command Airlift and Aerial Refueling Aircraft 

Mission Capable Rates 11

Table 3: Average Age and Number of Aircraft in Depot Maintenance 

Compared to Air Mobility Command’s Planned Numbers 

in Fiscal Year 1999 13

Table 4: Aircraft Average Not Mission Capable for Supply and 

Cannibalization Rates Compared to Air Mobility Command 

Standard Rates for Fiscal Year 1999 14

Table 5: Air Mobility Command Initiatives and Related Funding 

Dollars in Billions 17

Table 6: Air Mobility Command Airlift and Aerial Refueling 

Aircraft Data 30
Contents

Page 2 GAO/NSIAD-00-135 Military Readiness

Figures Figure 1: Relative Size of Various Airlift and Tanker Aircraft 8

Figure 2: Amount Funded Versus Required for Spare Parts for 

Fiscal Years 1991-99 15

Figure 3: C-5 Aircraft 22

Figure 4: C-141 Aircraft 23

Figure 5: C-17 Aircraft 24

Figure 6: KC-135 Aircraft 25

Figure 7: KC-10 Aircraft 26

Figure 8: Airlift Requirement Through Fiscal Year 2006 and 

Projected Shortfall 28

Figure 9: Aerial Refueling Requirement Through Fiscal Year 2021 29

Figure 10: C-5 Aircraft Required and Mission Capable, Fiscal Years 

1997-99 31

Figure 11: KC-135 Air Mobility Command Aircraft Required and 

Mission Capable, Fiscal Years 1997-99 32

Figure 12: KC-10 Aircraft Required and Mission Capable, Fiscal Years 

1997-99 33

Figure 13: Age of the C-5 Fleet as of December 1999 37

Figure 14: Age of the KC-135 Fleet as of September 1999 38

Figure 15: Age of the KC-10 Fleet as of January 2000 39

Figure 16: C-5 Average Depot Maintenance Days Fiscal Years 

1989-99 40

Figure 17: KC-135 Average Depot Maintenance Days Fiscal Years 

1992-99 41

Figure 18: C-5 NMCS Rates Compared to the Air Mobility Command 

Standard for Fiscal Years 1997-99 43

Figure 19: C-5 Cannibalizations per 100 Sorties Compared to the Air 

Mobility Command Standard for Fiscal Years 1997-99 44

Figure 20: KC-135 NMCS Rates Compared to the Air Mobility 

Command Standard for Fiscal Years 1997-99 45

Figure 21: KC-135 Cannibalizations Per 100 Sorties Compared to 

the Air Mobility Command Standard for Fiscal Years 

1997-99 46

Figure 22: KC-10 NMCS Rates Compared to the Air Mobility 

Command Standard for Fiscal Years 1997-99 47

Figure 23: KC-10 Cannibalizations Per 100 Sorties Compared to 

the Air Mobility Command Standard for Fiscal Years 

1997-99 48
Contents

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Abbreviations

AMC Air Mobility Command

DOD Department of Defense

MPF/D million pounds of fuel per day

MTM/D million-ton miles per day

NMCS not mission capable for supply
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United States General Accounting Office

Washington, D.C. 20548

National Security and

International Affairs Division

B-284769 Letr

June 22, 2000

The Honorable Herbert H. Bateman

Chairman, Subcommittee on Military Readiness

Committee on Armed Services

House of Representatives

Dear Mr. Chairman:

The National Military Strategy calls for U.S. forces to be able to deploy 

anywhere in the world to protect national interests. Having sufficient 

strategic airlift, sealift, prepositioned supplies and ground transportation is 

critical to the military’s ability to deploy worldwide. In your July 1999 letter 

to the Comptroller General, you raised a concern that U.S. mobility 

capabilities may be inadequate to quickly transport the military forces and 

supplies necessary to execute the National Military Strategy of fighting and 

winning two nearly simultaneous major theater wars. This report is the first 

in a series to assess the ability of U. S. mobility forces to achieve that 

strategy. It addresses the following issues: (1) Are the Air Force’s strategic 

airlift and aerial refueling fleets capable of meeting the requirements for 

winning two nearly simultaneous major theater wars? (2) What are the 

reasons for any shortfalls in strategic airlift and aerial refueling capability? 

(3) What Department of Defense (DOD) efforts are underway to resolve 

these capability shortfalls and what are the issues it faces in doing so? 

Appendix V describes the scope and methodology of our work.

Results in Brief DOD does not have sufficient airlift and aerial refueling capability to meet 

the two major theater war requirements because many aircraft needed to 

carry out wartime activities are not mission ready. For example, during 

fiscal years 1997 through 1999, on average only 55 percent of the C-5 fleet, 

the Air Force’s largest cargo aircraft, was mission capable1

—significantly 

short of the 75 percent expected for wartime. In total, we estimate DOD is 

short (1) over 29 percent of the needed military airlift capability and 

(2) nearly 19 percent of the needed refueling aircraft. While the shortfalls 

1

Mission capable means an aircraft can perform at least one and potentially all of its 

designated mission activities.
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do not mean the United States cannot win two major theater wars, the 

Office of the Joint Chiefs of Staff estimates that due to airlift shortfalls, 

military forces would arrive later than originally planned, thereby 

increasing the risk that war plans would not be executed in a timely 

manner and possibly increasing casualties.

Air Force Headquarters officials attribute the shortfalls in airlift and aerial 

refueling capability primarily to the age of the aircraft and spare parts 

shortages. Aircraft used for airlift are the C-5, C-141, and C-17; KC-135 

aircraft are used for aerial refueling; and KC-10 aircraft are used for both 

missions. (See app. I for descriptions of each aircraft.) The C-5 fleet, which 

ranges in age from 10 to 30 years, averages about 21 years old and the 

KC-135 fleet averages 39 years old. In recent years, the mission capability of 

these aging aircraft has declined primarily because of the increasing 

number of aircraft that need depot maintenance. Air Force data also show 

that C-5 and KC-135 aircraft have suffered lower mission capability due to 

shortages of spare parts.

The Air Mobility Command is considering spending $18 billion through 

fiscal year 2012 on airlift and aerial refueling aircraft. Its plans include 

buying C-17s and upgrading the C-5 and KC-135 aircraft. However, the 

results of ongoing DOD studies reevaluating airlift and refueling 

requirements and alternatives could increase future requirements, change 

budget priorities, and lead to the procurement of more aircraft.

In written comments on a draft of this report, DOD acknowledged that 

there are airlift and aerial refueling shortfalls but disagreed with our 

method of computing aircraft mission capable rates. It also disagreed that 

these shortfalls would limit DOD’s ability to meet the two major theater 

war requirements. Our calculations of aircraft mission capable rates, 

however, are consistent with Air Force war planning and DOD readiness 

reporting guidance. Our conclusion that DOD’s ability to meet two major 

theater war requirements could be limited by airlift shortfalls is consistent 

with DOD’s Quarterly Readiness Report to the Congress. We have included 

DOD’s comments throughout the report where appropriate.

Background The ultimate test for the military, according to the National Military 

Strategy, is for the United States to be able to win two major theater wars 

occurring nearly simultaneously. Air mobility would deliver the bulk of the 

initial time critical forces and supplies, and it is the cornerstone for the 

nation’s security strategy for the foreseeable future.
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Currently, DOD expects the U.S. Air Force, the Air National Guard, and the 

Air Force Reserves to use the C-5, C-141, C-17, and some KC-10 aircraft to 

carry many of the first forces overseas and support wartime operations. 

The military’s KC-135 and the KC-10 aircraft are expected to refuel these 

airlift aircraft in transit. The Air Force’s Air Mobility Command is 

responsible for managing and overseeing the readiness of the air mobility 

force. Figure 1 shows the relative size of the individual aircraft. 
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Figure 1: Relative Size of Various Airlift and Tanker Aircraft

Source: GAO.

Feet

C-5

C-17

C-141

KC-10

KC-135

240 200 160 120 80 40 0
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The total annual funding for operating, maintaining, and buying new airlift 

and aerial refueling aircraft increased from $8.95 billion in fiscal year 1988 

to $12.42 billion in fiscal year 1999 (constant 2000 dollars). As a percentage 

of DOD’s budget, the amount for airlift and aerial refueling has doubled 

since fiscal year 1988, from 2.3 to 4.6 percent, a small portion when 

compared to other major military functions such as tactical air forces (over 

11 percent) and land forces (over 18 percent). By fiscal year 2005, DOD 

projects airlift and aerial refueling funding will decrease to $11.85 billion 

(4.2 percent of DOD’s budget) because of a decline in the amount budgeted 

for procurement. Most of the procurement funds in recent years have gone 

toward purchasing C-17 aircraft and will continue to do so through fiscal 

year 2005.

DOD Does Not Have 

Sufficient Airlift and 

Aerial Refueling 

Capability

DOD does not have sufficient airlift and aerial refueling capability to meet 

the estimated two major theater war requirements. According to DOD, 

shortfalls are attributable to a combination of factors, including actual 

mission capable rates below Air Mobility Command standards, more 

aircraft in depot for longer periods than planned (which is factored into 

mission capable rate), and a temporary loss of capability as C-17s replace 

C-141s. As shown in table 1, based on average mission capable rates, 

military airlift is over 29 percent short of the million-ton miles per day 

(MTM/D)2

 requirement. Furthermore, the average number of refueling 

aircraft mission capable is nearly 19 percent short. Measured differently, 

the aerial refueling shortfall equals about 14 percent of the 106.1 million 

pounds of fuel per day (MPF/D)3

 total capacity.

2

MTM/D is a measure of airlift capacity that Air Mobility Command computes using a 

formula that is the product of the mission aircraft’s (available hours per day) (the nautical 

miles per hour) (the expected average load) (a factor that accounts for returning empty) and 

is divided by a million miles. It represents the fully mobilized wartime capability of all cargo 

airlift, including active duty, Air National Guard, Air Force Reserve, and civilian.

3

MPF/D is an Air Mobility Command measure of fuel offload capability cited in its Strategic 

Master Plan. It is computed using a formula that is the product of the aircraft (inventory) 

(sortie rate) (offload per sortie) and is divided by a million miles.
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Table 1: Airlift and Aerial Refueling Shortfall Based on Average Mission Capable Rates

a

Averages for C-5, KC-10, and KC-135 were based on rates for fiscal years 1997-99. Average for C-17 

and C-141 was based on fourth quarter fiscal year 1999.

Source: Computed based on U.S. Air Force, Air Mobility Command data.

In 1995, the Air Mobility Command identified the air transportation 

requirements to meet the two major theater war demands of the national 

strategy. It concluded that the military needed to be able to lift 49.7 MTM/D. 

Of that amount, 29.2 MTM/D were expected to be delivered by military 

aircraft and the remainder was expected to be delivered by civilian 

contracted aircraft. For war planning, the Air Mobility Command has 

identified the MTM/D each type of aircraft is expected to deliver. DOD’s 

1997 Report of the Quadrennial Defense Review reaffirmed the nearly 

50 MTM/D requirement.

According to the Air Mobility Command, the current number of refueling 

aircraft, while less than the classified requirement identified in 1996, is 

acceptable assuming the aircraft can be shifted between the two nearly 

simultaneous wars. DOD’s 1997 Report of the Quadrennial Defense Review 

did not change the aerial refueling requirement.

The Air Mobility Command’s determinations of the airlift and aerial 

refueling requirements and the ability of these forces to meet the 

requirements are based on the aircraft operating at standard wartime 

mission capable rates—the percentage of aircraft expected to be mission 

Mission

Military wartime 

requirement

Current peacetime 

capabilitya Shortfall (overage)

Percentage total

shortfall (overage)

C-5 12.98 MTM/D 9.52 MTM/D 3.46 MTM/D 11.85

KC-10 3.08 MTM/D 3.19 MTM/D (0.11)MTM/D (0.37)

C-17/C-141 13.14 MTM/D 7.93 MTM/D 5.23 MTM/D 17.90

Total military airlift 29.20 MTM/D 20.64 MTM/D 8.58 MTM/D 29.38

KC-135 402 aircraft 317 aircraft 85 aircraft 19.19

KC-10 41 aircraft 42 aircraft (1) aircraft (0.23)

Total refueling aircraft 443 aircraft 359 aircraft 84 aircraft 18.96

KC-135 74.8 MPF/D 59.0 MPF/D 15.8 MPF/D 14.9

KC-10 31.3 MPF/D 32.4 MPF/D (1.1)MPF/D (1.0)

Total refueling capacity 106.1 MPF/D 91.4 MPF/D 14.7 MPF/D 13.9
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capable. However, Air Mobility Command data show that many of the 

aircraft are not achieving these rates in recent years. During fiscal 

years 1997-99, the C-5 and KC-135 average mission capable rates did not 

achieve the standard, but the KC-10’s average mission capable rate was 

slightly higher than the standard. The C-141 and C-17 rates were below the 

mission capable standard in the fourth quarter of fiscal year 1999 (see table 

2). Because the C-141s are being replaced by C-17s, the Air Mobility 

Command expects the C-141 shortfall to be eliminated by 2004. Therefore, 

we considered the performance of the other aircraft of greater concern.

Table 2: Air Mobility Command Airlift and Aerial Refueling Aircraft Mission Capable 

Rates

a

Average mission capable rates for the C-5, KC-135, and KC-10 were based on rates for fiscal years 

1997-99. Average mission capable rates for the C-141 and C-17 were based on fourth quarter fiscal 

year 1999 data because these aircraft are in transition. These rates were computed by dividing the 

number of aircraft mission capable by the total number of primary mission aircraft.

b

Rate does not include mission capability of 30 KC-135s assigned outside of Air Mobility Command.

Source: U.S. Air Force, Air Mobility Command.

In fiscal years 1997 through 1999, the C-5’s mission capable rate averaged 

55 percent (57 of 104 aircraft). This average is less than the 75-percent Air 

Mobility Command mission capable rate standard. At a 55-percent mission 

capability rate, the C-5 fleet is nearly 3.5 MTM/D short of its expected airlift 

contribution to two major theater wars. This deficit is of particular concern 

because of the C-5’s ability to carry large cargo. Air Mobility Command 

officials said that if they needed to surge aircraft for wartime deployment, 

the C-5’s initial shortfall may be reduced by increasing maintenance and 

aircrew availability, temporarily delaying some periodic maintenance 

activities, accelerating aircraft through maintenance, using training 

aircraft, and flying aircraft that would normally be considered not mission 

capable. Air Mobility Command officials could not quantify how quickly 

these steps would affect aircraft availability.

Mission capable rates (percent)

Aircraft type

Air Mobility Command standard

wartime rates

Averagea peacetime

rates

C-5 75 55

C-17 87.5 66

C-141 80 61

KC-135 85 67b

KC-10 85 88
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Over the past 3 fiscal years, Air Mobility Command’s KC-135s have also 

performed below its 85 percent mission capable rate standard, by 

averaging 67 percent. At a 67-percent rate, the KC-135 fleet is about 

85 aircraft and 15.8 MPF/D short of the expected refueling requirement. 

According to Air Mobility Command officials, they would employ 

management initiatives similar to those cited for the C-5 to increase the 

number of refueling aircraft available should more aircraft be needed. 

Again Air Mobility Command officials could not identify how quickly these 

steps would affect aircraft availability.

The KC-10’s performance over the past 3 fiscal years has been above the 

85-percent standard rate at 88 percent. Because the aircraft is used for both 

airlift and aerial refueling missions, its higher mission capable rate reduces 

shortfalls in both missions. At an 88-percent mission capable rate, the 

KC-10 reduced the airlift shortfall by 0.1 MTM/D. When added to the 5.2 

MTM/D shortfall anticipated in the fourth quarter of fiscal year 1999 due to 

the C-17 replacing the C-141 and lower than expected mission capable 

rates, DOD is over 29 percent (8.6 of 29.2 MTM/D) short of the military 

airlift requirement. The higher KC-10 mission capable rate reduces the total 

aerial refueling aircraft shortfall by 1 aircraft, or 1.1 MPF/D to 14.7 MPF/D.

The Office of the Joint Chiefs of Staff, through its classified Joint Monthly 

Readiness Reviews, determined in fiscal year 1999 that air mobility 

shortfalls would not preclude U.S. forces from winning two major theater 

wars but could delay implementation of war plans. DOD has reported to 

the Congress that these delays could increase the potential for higher 

casualties in the interim and during the warfight. These reviews examined 

the impact of the air mobility fleet’s mission capable status on the U.S. 

military’s ability to win two nearly simultaneous major theater wars and 

other scenarios involving ongoing small-scaled operations. Such analyses 

determined the risks associated with the timely arrival of forces and the 

ability to move to a second war. In its latest risk assessment to the 

Congress, DOD acknowledged that the United States is at high risk in the 

second major theater war, in part, due to current airlift shortfalls. 

Furthermore, some analyses showed that risks increased for even one 

major theater war when U.S. forces were engaged in a Kosovo-size 

contingency because it exacerbated the shortages in engines and spare 

parts. (See app. II for more details on airlift and aerial refueling 

requirements, aircraft mission capable trends for the last 3 fiscal years, and 

the impact of current mission capability on executing war plans.)
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Aging Aircraft and 

Spare Parts Shortages 

Cause Low Mission 

Capability Rates

According to Air Force Headquarters officials, aging aircraft and 

insufficient quantities of spare parts are the two primary reasons airlift and 

aerial refueling aircraft are performing below the Air Mobility Command 

mission capable standard rates. As aircraft age, more maintenance 

problems arise. As a result, the number of aircraft not mission capable 

increases because more aircraft are in depot maintenance than the Air 

Mobility Command planned (see table 3). In addition, the time it takes to 

perform aircraft depot maintenance generally increases with the age of the 

aircraft. For example, from fiscal years 1992 through 1999, the average 

number of days for KC-135s to complete depot maintenance more than 

doubled, from 170 days to 374 days due to rework of wings and other 

structural items, corrosion prevention measures, and rewiring. (See app. III 

for more information on aircraft age and the depot trends over time.)

Table 3: Average Age and Number of Aircraft in Depot Maintenance Compared to Air 

Mobility Command’s Planned Numbers in Fiscal Year 1999

a

Approximately 16 aircraft per quarter were undergoing a one-time avionics modification.

Source: U.S. Air Force, Air Mobility Command.

For years, having insufficient spare parts has also been recognized as a 

major contributor to aircraft performing at lower mission capable rates 

than expected. The Air Force measures the impact of parts shortages on 

aircraft availability by citing a not mission capable for supply (NMCS) rate 

that reflects the percentage of aircraft not meeting mission requirements 

because parts needed for repairs are not available. The Air Force also 

tracks the number of times parts are removed from one aircraft to fix 

another, which is called the cannibalization rate. Table 4 compares the 

fiscal year 1999 NMCS and cannibalization rates to the Air Mobility 

Command standard rates for each. It shows that due to the lack of spare 

parts, the C-5’s and KC-135’s average rates exceeded both standards, while 

only the KC-10’s cannibalization rate exceeded the standard. (See app. IV 

Number of aircraft in depot 

(monthly average)

Aircraft type Average age (years) Planned Actual

C-5 21 16 36

KC-135 39 52 124a

KC-10 15 5 10
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for more details on the extent to which these aircraft were NMCS and 

cannibalized for parts during fiscal years 1997 through 1999.)

Table 4: Aircraft Average Not Mission Capable for Supply and Cannibalization Rates 

Compared to Air Mobility Command Standard Rates for Fiscal Year 1999

a

Percentage of aircraft that cannot meet mission requirements because they lack parts.

b

Number of cannibalizations per 100 flights.

Source: U.S. Air Force, Air Mobility Command.

Despite long-standing insufficient spare part problems, the Air Force has 

not consistently provided all of the funds its forces said are required to buy 

spare parts. As shown in figure 2, since fiscal year 1991, the Air Force has 

fully funded what it identified as the total requirement for spare parts only 

twice—in fiscal years 1995 and 1999. 

Not mission capable for supply 

ratea Cannibalization rateb

Aircraft type Average Standard Average Standard

C-5 17.75 8.5 54.93 19.6

KC-135 12.65 8.5 11.05 4

KC-10 4.47 5 4.51 3
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Figure 2: Amount Funded Versus Required for Spare Parts for Fiscal Years 1991-99

Source: U.S. Air Force, Deputy Assistant Secretary (Budget).

We reported in 19954 and again in 19995 that the C-5 had not been achieving 

the 75-percent mission capable rate, in part, because it lacked spare parts. 

DOD responded to the 1995 report by saying that Air Force initiatives to 

fully fund C-5 operations, provide increased spare parts funding, and fund 

modifications would improve the aircraft’s readiness, but not visibly until 

1997. The Air Force increased C-5 spare parts funding from 76 percent of 

requirements in fiscal year 1994 to 100 percent in fiscal year 1996. However, 

funding then decreased to 80 percent of requirements in fiscal year 1997. 

Our 1999 report stated that the parts shortage was due, in part, to DOD’s 

weaknesses in forecasting inventory requirements and the failure of its 

logistics system to achieve expected inventory management 

Requirement

Funded

91 92 93 94 95 96 97 98 99

Fiscal Years

0

1

2

3

4

5 $ Billions

4

Strategic Airlift: Improvements in C-5 Mission Capability Can Help Meet Airlift 

Requirements (GAO/NSIAD-96-43, Nov. 20, 1995).

5

Air Force Supply: Management Actions Create Spare Parts Shortages and Operational 

Problems (GAO/NSIAD/AIMD-99-77, Apr. 29, 1999).
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improvements. We also noted that to support the mission capability rates at 

that time, the Air Force was routinely cannibalizing parts and using parts 

from the units’ war reserve kits that support deployed operations. DOD 

again responded that Air Force initiatives would fix the problem.

In 1999, the Air Force received an additional $904 million in obligation 

authority to buy more spare parts. This amount consisted of $387 million to 

buy spares attributable to the Kosovo Operation, $135 million to the 

Oklahoma City Air Logistics Center, and $382 million to overcome the 

accumulated shortfall in spare part inventories. According to the Air Force 

Material Command, some of this money is to go to the C-5 and the KC-135. 

Despite this increase, Air Force officials state that spare part shortages will 

continue to be a problem in the near term because it will take 18 to 

24 months for increased consistent funding to improve the availability of 

spares.

Modernization Plans 

Are Being Reevaluated, 

Causing DOD to Face 

Difficult Choices

Currently, the Air Mobility Command plans to invest $18 billion through 

2012 upgrading the C-5 and KC-135 and buying C-17 aircraft (see table 5). 

According to DOD, the C-5 and KC-135 upgrades and purchase of 120 C-17s 

will slightly improve capability and reduce operating and support costs. 

After the delivery of the 120 C-17s is completed, DOD stated it will be able 

to increase planned airlift capability from 46 MTM/D in 1999 to 50 MTM/D 

by 2005 and buying 14 additional C-17s, beginning in fiscal year 2003, would 

further increase its capability. However, several studies underway could 

increase air mobility requirements, increase the number of aircraft DOD 

wants to buy, and change the extent and timing of aircraft upgrades. Such 

changes would cause DOD to face difficult choices in deciding how to 

resolve the shortfalls.
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Table 5: Air Mobility Command Initiatives and Related Funding Dollars in Billions

Source: U.S. Air Force, Air Mobility Command and DOD comments.

The Air Mobility Command had expected to eliminate the airlift shortfall in 

2004 by buying 134 C-17s to replace the 266 C-141s. According to DOD 

estimates, it will have bought 85 C-17s at a cost of $25.4 billion by the end 

of fiscal year 2000. Buying the remaining 49 aircraft is expected to cost 

about $12.4 billion through fiscal year 2005.

Because of the C-5’s low mission capable rates, the Air Mobility Command 

is considering upgrading the aircraft at a cost of $5.3 billion. The upgrade 

program involves replacing the engine; strengthening the structure; and 

upgrading many of the aircraft’s auxiliary power, electric, hydraulics, and 

other systems. The funding for the program would be budgeted through 

fiscal year 2012.

According to DOD officials, the planned upgrades to the KC-135 are to 

improve its capabilities, not its mission capable rate. However, the Air 

Mobility Command is spending approximately $300 million through fiscal 

year 2006 to replace some engines and perform some other minor actions 

that, according to Air Force officials, will improve the fleet’s 

maintainability and reliability. Although the Air Mobility Command has 

forecasted that a replacement for the KC-135 should be entering the 

inventory in fiscal year 2013, the funding for this replacement has not been 

identified, even though it is reasonable to assume funds would be required 

well before then.

All of these plans could be significantly affected by a number of studies 

underway. The most significant of these may be the Mobility Requirements 

Study 2005. The results of this study, according to Air Mobility Command 

officials, may not be reported until September 2000. The focus of this study 

Action Fiscal year Amount Comments

C-17 aircraft purchase 2001-2003 $8.2 The last 35 of 120 C-17s are being purchased to replace the 

C-141s on an equal capacity basis.

C-17 additional aircraft 

purchase

2003-2005 4.2 14 additional C-17s purchased to increase operational 

flexibility and yield a net increase in overall capability.

C-5 aircraft upgrades 2001-2012 5.3 Reliability and maintainability improvements that reduce 

overall ownership costs.

KC-135 aircraft upgrades 2001-2006 0.3 Reduces crew size and lowers ownership costs.

Total $18.0
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is to determine the capability that is needed to win two nearly simultaneous 

major theater wars. It will examine issues such as the impact of deploying 

forces already dispersed in small-scaled contingencies around the world, 

effects of chemical and biological weapons on mobility, and the effect of 

support provided by host nations. These issues, according to Air Mobility 

Command officials, will almost certainly increase the amount of airlift and 

aerial refueling that is required.

Other ongoing studies that are examining aircraft economic service life and 

aerial refueling requirements include an evaluation of how to overcome the 

C-5 airlift shortfall and a tanker requirements study. The results of these 

studies, when coupled with the Mobility Requirement Study 2005 results, 

could have significant force size and budget implications. For example, the 

C-5 study examines nine alternatives for providing the same heavy lift 

capability currently expected of that aircraft. The alternatives include the 

replacement of C-5s, various combinations of upgraded C-5s, and the 

purchase of additional C-17s. The tanker requirements study could suggest 

increasing the number of refueling aircraft required. According to Air 

Mobility Command officials, the cost to replace the 546 aircraft in the 

KC-135 fleet could be significant and at a pace of 15 to 20 aircraft a year, it 

could take a substantial period of time.

Based on these study results, DOD will face difficult choices about how to 

resolve the current airlift and refueling capability shortfalls. These choices 

will likely involve one or a combination of the following options, each of 

which carries some risk.

• Do not change current plans and accept associated risks. DOD would 

follow through on its scheduled purchase of C-17s to replace the C-141s 

and upgrade the C-5 and KC-135 aircraft. It would continue employing 

workarounds to overcome any temporary capability shortfalls should 

the aircraft mission capable rates not achieve standards.

• Decrease requirements by adjusting war plans to allow more time for 

deploying forces into theater or planning for less than two nearly 

simultaneous major theater wars. For example, allowing more time for 

the arrival of forces into a theater would reduce the peak demand for 

airlift and aerial refueling. Reducing the size of the ground and combat 

air forces to transport overseas would also decrease the cargo 

requirements. Planning for less than two nearly simultaneous major 

theater wars would reduce the overall tonnage and refueling 

requirement.
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• Reduce peacetime operational commitments, thereby limiting the 

number of airlift and aerial refueling flights to the level commensurate 

with sustaining the mission capable standards. Limiting the number of 

aircraft available to support peacetime deployments could reduce the 

fleets’ demand for spare parts, thereby reducing the number not mission 

capable and increasing mission capable rates. 

• Prioritize funding for airlift and aerial refueling operations and 

modernization to the levels commensurate with achieving and 

sustaining the desired capability levels.

Agency Comments and 

Our Evaluation 

In its comments on a draft of this report, DOD disagreed with our report 

and overall conclusion that DOD does not have sufficient airlift and air 

refueling capability to meet the two major theater war requirement because 

many aircraft are not mission ready. DOD acknowledged that shortfalls in 

airlift and aerial refueling capabilities are made worse by chronic spare 

part shortages and excessive aircraft in depot maintenance. However, it 

asserted that our report overstates the current mission capability shortfall 

and does not recognize that some of the reasons for the shortfall are 

normal characteristics during peacetime. Furthermore, DOD said we 

erroneously characterized its $18 billion planned airlift and aerial refueling 

investments to modernize the fleet as an effort to overcome the large 

mission capability shortfall.

We disagree with DOD’s statement that we overstated the airlift and aerial 

refueling shortfall. As our report points out, our shortfall computations 

were based on methodology that is consistent with Air Force airlift 

warplanning guidance and DOD’s October 1999 guidelines for reporting 

equipment readiness to the Congress. We also believe that comparing the 

fleet’s readiness status to the wartime requirement is the appropriate way 

to assess the readiness of the airlift and aerial refueling aircraft for the 

onset of two major theater wars. As to not recognizing that lower mission 

capable rates are a normal characteristic of peacetime operations, we 

believe the large number of aircraft consistently in depots, the duration of 

their maintenance, and the current parts shortage would delay their 

availability for deployment in the event of crisis. Furthermore, we state in 

the report that management actions could be taken to reduce the shortfall 

if a deployment surge occurs. However, we note that Air Mobility 

Command officials could not identify how quickly these actions could be 

completed and provide the aircraft needed for a wartime surge.
B-284769

Page 20 GAO/NSIAD-00-135 Military Readiness

Appendix VI contains the full text of DOD’s comments and our evaluation 

of them. DOD also provided technical comments, which we incorporated 

as appropriate. 

We are providing copies of this report to the appropriate congressional 

committees and the Honorable William S. Cohen, Secretary of Defense and 

the Honorable F. Whitten Peters, Secretary of the Air Force. Copies will 

also be made available to others upon request.

If you or your staff have questions concerning this report, please call me at 

(757) 552-8111. The major contributors to this report are listed in 

appendix VII.

Sincerely yours,

Neal P. Curtin

Associate Director

National Security Preparedness Issues
Page 21 GAO/NSIAD-00-135 Military Readiness
Page 22 GAO/NSIAD-00-135 Military Readiness

Appendix I

Airlift and Refueling Aircraft ApApenednxidexiIs

The Air Mobility Command is responsible for providing global airlift 

services and air refueling operations. To carry out its mission, it has the C-5, 

C-141, and C-17 to transport equipment and supplies and the KC-135 and 

KC-10 to refuel aircraft. The KC-10 aircraft is also used for transporting 

equipment and supplies. Figures 3 to 7 show the individual aircraft.

Figure 3: C-5 Aircraft

Source: U.S. Air Force.

The C-5 is one of the largest aircraft in the world. It can carry 

291,000 pounds of large cargo for 1,530 nautical miles without refueling and 

can take off fully loaded in 8,300 feet or land in 4,900 feet. The aircraft 

length is 247 feet and height is 65 feet with a wing span of 223 feet. The C-5 

has a distinctive high T-tail, a 25-degree wing sweep, and four turbofan 

engines mounted on pylons beneath the wings. Ground crews can load and 

unload the C-5 simultaneously at the front and rear cargo openings since 

the nose and aft doors open the full width and height of the cargo 

compartment. It can also “kneel down” to facilitate loading directly from 

truck bed levels and can carry nearly all of the Army’s combat equipment, 

including large heavy items as the 74-ton mobile scissors bridge.
Appendix I

Airlift and Refueling Aircraft

Page 23 GAO/NSIAD-00-135 Military Readiness

Figure 4: C-141 Aircraft

Source: U.S. Air Force.

The C-141 fills many airlift requirements through its ability to airlift combat 

forces over long distances, deliver those forces and their equipment either 

by landing or airdrop, resupply forces, and transport the sick and wounded 

from the hostile area to medical facilities. The newer C-141s can carry 

68,000 pounds of large cargo for 2,270 nautical miles without refueling. The 

aircraft length is 168 feet and height is 39 feet with a wing span of 160 feet. 

The C-141 fleet, nearing 9 million flying hours, is being replaced by the 

C-17.
Appendix I

Airlift and Refueling Aircraft

Page 24 GAO/NSIAD-00-135 Military Readiness

Figure 5: C-17 Aircraft

Source: U.S. Air Force.

The C-17 is the newest, most flexible cargo aircraft to enter the airlift force. 

The C-17 is capable of rapid strategic delivery of troops and all types of 

cargo to main operating bases or directly to forward bases near the front 

lines. The aircraft is also able to perform airdrop missions when required. 

The C-17 can carry 160,000 pounds of large cargo for 2,400 nautical miles 

without refueling, can take off fully loaded and land in 3,000 feet, and can 

carry almost all of the Army’s air-transportable equipment. The aircraft 

length is 174 feet and height is 55 feet with a wing span of 170 feet. The C-17 

will be considered the primary military airlift aircraft once it replaces the 

C-141s.
Appendix I

Airlift and Refueling Aircraft

Page 25 GAO/NSIAD-00-135 Military Readiness

Figure 6: KC-135 Aircraft

Source: U.S. Air Force.

The KC-135’s principal mission is air refueling, which enhances the U. S. Air 

Force’s capability to accomplish its global missions. The aircraft also 

provides aerial refueling support to U.S. Navy, U.S. Marine Corps, and allied 

aircraft. The KC-135 can carry 150,000 pounds of fuel for 1,500 nautical 

miles. The aircraft length is 136 feet and height is 42 feet with a wing span 

of 131 feet. A cargo deck above the refueling system can hold a mixed load 

of passengers and cargo.
Appendix I

Airlift and Refueling Aircraft

Page 26 GAO/NSIAD-00-135 Military Readiness

Figure 7: KC-10 Aircraft

Source: U.S. Air Force.

The KC-10 is an Air Mobility Command advanced tanker and cargo aircraft 

designed to increase global mobility for U.S. armed forces. The aircraft 

length is 182 feet and height is 58 feet with a wing span of 165 feet. The 

KC-10 has 6 large fuel tanks with a combined capacity of more than 

356,000 pounds of fuel–over twice as much as the KC-135. Using either an 

advanced aerial refueling boom or a hose and drogue refueling system, the 

KC-10 can refuel a wide variety of U.S. and allied military aircraft on the 

same flight.

Although the KC-l0’s primary mission is aerial refueling, it can combine the 

tasks of a tanker and cargo aircraft by refueling fighters and simultaneously 

carrying the fighter support personnel and equipment on overseas 

deployments. The KC-10 can transport up to 75 people and nearly 

170,000 pounds of cargo a distance of about 4,400 miles without refueling.
Page 27 GAO/NSIAD-00-135 Military Readiness

Appendix II

Current Airlift and Aerial Refueling Capability ApendxiI

The Department of Defense (DOD) does not have sufficient airlift and 

aerial refueling capability to initially meet the two major theater war 

requirements. Its military airlift capability is over 29 percent short of the 

wartime requirement—almost 12 percent of the shortfall is due to the C-5 

aircraft performing below Air Mobility Command’s mission capability1

expectations. Nearly 18 percent is due to insufficient airlift capability while 

the C-17 replaces the C-141. DOD’s aerial refueling capability is nearly 

19 percent short of the required number of aircraft because the KC-135 is 

performing below Air Mobility Command’s standard. According to DOD, air 

mobility shortfalls add risk to its ability to execute war plans.

Airlift Falls Short of 

Requirements

In 1981, 1992, and 1995, DOD identified its airlift requirements. In 1981, 

DOD issued its Congressionally Mandated Mobility Study2

 that set a 

66-million ton miles per day (MTM/D) objective for strategic airlift. In 1992, 

after the fall of the former Soviet Union, DOD performed a Mobility 

Requirement Study that showed a need to airlift 57 MTM/D to provide the 

forces needed for two major theater wars. The 1995 Mobility Requirements 

Study Bottom Up Review Update further reduced the airlift requirement to 

49.7 MTM/D. Military cargo aircraft were expected to deliver about 

29 MTM/D of the 1995 requirement and contracted aircraft called the civil 

reserve air fleet would transport the remainder.

The Air Mobility Command has acknowledged that it does not have 

sufficient military airlift and refueling capabilities. These conclusions are 

based on a comparison of the assumed number of mission capable airlift 

and aerial refueling aircraft versus the two major theater war requirements. 

An Air Mobility Command estimate provided in September 1999 showed 

the expected contributions that various levels of the contracted civilian 

aircraft and each type of military airlift aircraft will make (see fig. 8). 

Despite plans to replace the 141s with C-17s, the Command still expects to 

be short airlift at least through fiscal year 2006, as the figure shows.

1

Mission capable refers to the condition of an aircraft indicating it can perform at least one 

and potentially all of its designated missions.

2

Department of Defense Authorization Act, 1981, Pub. L. 96-342, § 203(b), 94 Stat. 1077, 1080 

(1980).
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 28 GAO/NSIAD-00-135 Military Readiness

Figure 8: Airlift Requirement Through Fiscal Year 2006 and Projected Shortfall

Source: U.S. Air Force, Air Mobility Command.

Aerial Refueling Falls 

Short of Requirements

The Air Mobility Command’s last comprehensive aerial refueling 

requirement study was in 1996. The classified results for two major theater 

wars were stated in terms of the number of aircraft and million pounds of 

fuel per day (MPF/D) necessary to support the war time military airlift and 

combat aircraft operations. According to the Command, the military does 

not have sufficient aircraft in the refueling fleet to meet the requirement 

without shifting refueling aircraft between wars. DOD’s current guidance to 

the Command is to maintain at least the current refueling forces through 

fiscal year 2005. As a result, according to the Command, about 600 KC-135 

and KC-10 aircraft are needed (see fig. 9). They can provide approximately 

106 MPF/D. The Command anticipates sustaining the fleet size by replacing 

0

10

20

30

40

50

60

70

1987 1988 1989 1990 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Civil Reserve

KC-10

C-141

C-17

C-5A/B

Shortfall

1995

1992

1981

MTM/D

Fiscal Year
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 29 GAO/NSIAD-00-135 Military Readiness

the KC-135 with a new refueling aircraft (labeled KC-X) beginning in about 

fiscal year 2013.

Figure 9: Aerial Refueling Requirement Through Fiscal Year 2021

Source: U.S. Air Force, Air Mobility Command.

Aircraft Mission 

Capability Rates Fall 

Short of Standards

The Air Mobility Command’s airlift and aerial refueling aircraft mission 

capability data3

 show that for fiscal years 1997-99 the C-5 and KC-135 

aircraft have not operated at the expected levels necessary to meet 

requirements for the two major theater wars. Their reduced performance 

contributes to a shortfall of over 29 percent in military airlift and nearly

19 percent of aerial refueling aircraft, or about 14 percent of its capacity.

0

100

200

300

400

500

600

700

99 02 05 08 11 14 17 00 03 06 09 12 15 18 01 04 07 10 13 16 19 20 21

Fiscal Year

Number of Aircraft

KC-X

KC-10

KC-135

3

Some of DOD’s aircraft status reports show different numbers because they focus on the 

number of aircraft that units possess, whereas our analysis is based on the number of 

aircraft that are anticipated to meet wartime airlift and aerial refueling requirements.
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 30 GAO/NSIAD-00-135 Military Readiness

The Air Mobility Command’s determinations of the airlift and aerial 

refueling requirements, contributions by aircraft, and shortfalls (see figs. 8 

and 9) are based on airlift and aerial refueling aircraft achieving expected 

mission capable rates. Table 6 shows the total number of each type of 

aircraft, the number authorized to Air Mobility Command units, and the 

standard mission capable rates needed to meet wartime requirements. It 

also shows the number of mission capable aircraft needed based on the 

standard rates and the number of aircraft reported as mission capable. 

Rates for the C-5, KC-135, and KC-10 aircraft are based on fiscal years 1997-

99 data. Because the C-17 and C-141 are in transition, their rates are based 

on fourth quarter fiscal year 1999 information.

Table 6: Air Mobility Command Airlift and Aerial Refueling Aircraft Data

a

Excludes aircraft in inventory reserved for backup and training.

b

Percentage of mission authorized aircraft needed to meet wartime requirements.

c

The mission capable rate times the number of mission authorized aircraft.

d

The equivalent number of aircraft is based on the number of mission capable hours that units 

reported.

e

Actual percentage of authorized aircraft that are mission capable is based on the number of mission 

capable hours that units report.

f

Air Mobility Command only tracks 442 KC-135 authorized aircraft and 30 KC-135s are assigned to 

other commands. The 67-percent average mission capable rate for 442 aircraft was used to compute 

the mission capable numbers for all 472 aircraft.

Source: U.S. Air Force, Air Mobility Command.

While four of five aircraft types are performing below standards, the C-141s 

are to be replaced by new C-17s, which are just entering the inventory. 

Therefore, the C-5, KC-135, and KC-10 aircraft are of greater concern. 

Although the mission capable rate of the KC-10 (88 percent) is above 

standard (85 percent), its performance is important because it helps meet 

both airlift and aerial refueling requirements.

Type of 

aircraft

Total number

of aircraft

Total mission

authorized

aircrafta

Standard

mission

capable

ratesb

Equivalent

number of

aircraft

neededc

Equivalent number

of aircraft mission

capabled

Average

aircraft

mission

capable ratese

Number of

aircraft short

(over)

C-5 126 104 75 78 57 55 21

C-17 52 44 87.5 39 29 66 10

C-141 172 135 80 108 83 61 25

KC-135 546 472 85 402 317 f 67 f 85 f

KC-10 59 48 85 41 42 88 (1)
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 31 GAO/NSIAD-00-135 Military Readiness

As shown in figure 10, since the beginning of fiscal year 1997, the largest 

number of mission capable C-5s has been about 64 aircraft (61.5 percent of 

the 104 authorized aircraft in the fleet). This number is well below the 

78 aircraft identified in table 6 as required to meet war plans. During the 

period corresponding with the Kosovo Operation (March through July 

1999), as few as 44 C-5s were mission capable (42.3 percent of 104 aircraft).

Figure 10: C-5 Aircraft Required and Mission Capable, Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

Should only 55 percent of the C-5 mission authorized aircraft (about 

57 aircraft) and 88 percent of the KC-10s (about 42 aircraft) be mission 

capable at the start of a war, DOD could be 3.4 MTM/D short in military 

airlift—almost 12 percent. When added to the more than 5.2 MTM/D 

shortfall in the fourth quarter of fiscal year 1999 attributable to the C-17 and 

C-141, the total shortfall is nearly 8.6 MTM/D, or over 29 percent of the 

military portion of the requirement.

The C-5 fleet’s low mission capable rate is of particular concern because 

(1) this aircraft will lift less cargo to a theater than is expected and (2) the 

C-5 carries the greatest amount of large cargo, such as Army tanks. An 

Required C-5

Equivalent Mission Capable C-5

96 97 98

30

40

50

60

70

80

90

100

Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug 
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 32 GAO/NSIAD-00-135 Military Readiness

analysis of one major theater war scenario showed that about 70 percent of 

the cargo required in the critical first 30 days would be this type of cargo. 

Air Mobility Command officials said the C-5’s initial shortfall may be 

resolved by management initiatives such as withdrawing aircraft from 

depots, flying aircraft that would normally be considered not mission 

capable, and using aircraft assigned for training pilots.

The Air Mobility Command aerial refueling fleet has also been operating 

below its desired mission capability level. During fiscal years 1997-99, the 

number of equivalent mission capable KC-135s assigned to Air Mobility 

Command active and reserve forces peaked at about 347 aircraft 

(79 percent of the 442 authorized aircraft) versus 376 aircraft (the 

85-percent standard). However, the number had declined to 194 aircraft 

(44 percent of 442 authorized aircraft) by September 1999 (see fig. 11). 

According to the Air Mobility Command, during the Kosovo Operation, the 

number of tanker aircraft involved approximated a major theater war 

commitment—thereby straining the fleet.

Figure 11: KC-135 Air Mobility Command Aircraft Required and Mission Capable, Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

Required KC-135

Equivalent Mission Capable KC-135

96 97 98

Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug

150

200

250

300

350

400

450
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 33 GAO/NSIAD-00-135 Military Readiness

A major contributor to the KC-135’s mission capable decline since July 1999 

has been the failure of fuel tanks, a flight control system in the tail section, 

and some gears. Air Mobility Command officials said they expect to fix 

these problems by September 2000. Data show the KC-135’s mission 

capable rate has improved from a low of 44 percent (194 aircraft) in 

September 1999 to 52 percent (229 aircraft) in February 2000.

As noted previously, the KC-10s are expected to not only provide airlift but 

also aerial refueling capability. For 2 months during fiscal years 1997 

through 1999, as many as 46 KC-10s (96 percent of the 48 mission 

authorized aircraft) were mission capable, exceeding the 41 expected 

based on an 85-percent mission capable standard. However, the number of 

mission capable KC-10s had declined to 39 (81 percent of 48) in September 

1999. Moreover, KC-10 mission capability was more frequently below the 

level expected in fiscal year 1999 than in the previous 2 years (see fig. 12). 

The KC-10’s average mission capability in fiscal years 1997-99 slightly 

reduces the airlift and aerial refueling shortfalls.

Figure 12: KC-10 Aircraft Required and Mission Capable, Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

30

35

40

45

50

Oct96Nov Dec Jan97Feb Mar Apr May Jun Jul Aug Sep Oct97Nov Dec Jan98Feb Mar Apr May Jun Jul Aug Sep Oct98Nov Dec Jan99Feb Mar Apr May Jun Jul Aug Sep99

Required KC-10

Equivalent Mission Capable KC-10
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 34 GAO/NSIAD-00-135 Military Readiness

Should the KC-135 and KC-10 fleets’ mission capability rates be 67 percent 

and 88 percent, respectively, at the beginning of a war, DOD would be 

84 aircraft (nearly 19 percent) or 14.7 MPF/D (nearly 14 percent) short of 

expected refueling capability. According to Air Mobility Command officials, 

several 1999 Joint Chiefs of Staff analyses showed that because of the 

KC-135’s low mission capability rates, DOD would have to employ 

numerous workarounds to ensure sufficient aerial refueling. The 

workarounds might include deferring depot maintenance, accelerating 

aircraft through their final days of depot maintenance, and flying some 

aircraft with missing or broken parts, which would not affect flight safety 

but would normally make them not mission capable.

Current Mission 

Capability Shortfalls 

Add Risk to Executing 

War Plans

The Joint Chiefs of Staff, through its Joint Monthly Readiness Review 

process, has examined the impact of readiness deficiencies on the ability of 

U.S. forces to win two major theater wars and other scenarios involving 

participation in small-scaled contingencies at the onset of war. It has also 

elevated airlift deficiencies as concerns and provided a means to track 

progress in resolving them. Although the details are classified, the Joint 

Monthly Readiness Reviews showed that degraded airlift and refueling 

capabilities would increase risks associated with DOD’s ability to 

implement the two major theater war plans in a timely manner. 

Furthermore, risks would increase for even one major theater war when 

U.S. forces are already engaged in a Kosovo size small-scale contingency. 

The analyses did not conclude that the adverse impact would jeopardize 

the ultimate ability of the United States to win. However, the air mobility 

shortfalls increased (1) the time lines to halt the enemy and start the 

counteroffensive and (2) delays in these timelines add the potential for 

higher casualties in the interim and during the war.

Steps taken by the Air Mobility Command after the Kosovo Operation 

illustrated the potential adverse impact of low mission capable rates on air 

mobility. Even though, according to the Air Mobility Command, the Kosovo 

effort was less than for a major theater war, the cannibalization and spare 

parts problems for airlift and aerial refueling aircraft were serious. To 

alleviate these problems, the Command allowed the airlift and aerial 

refueling forces to reduce their availability for at least 120 days after the 

operation. For example, Dover Air Force Base, which is host to a large 

number of C-5s, did not make the usual 65 percent of its aircraft available 

for flying. It operated at 55 percent availability for 90 days and 60 percent 

for an additional 30 days. Dover Air Force Base officials told us this 

allowed Dover time to rebuild the spare parts supply and improve mission 
Appendix II

Current Airlift and Aerial Refueling 

Capability

Page 35 GAO/NSIAD-00-135 Military Readiness

capable rates. The Command’s action of lowering aircraft availability levels 

following Kosovo for all tanker and airlift forces so they could recover from 

such an operation raises speculation about how quickly and effectively the 

aircraft could immediately shift from such an operation to meet one major 

theater war requirement. Air Mobility Command officials have also 

expressed concern about the loss of flexibility to respond to multiple 

missions after the 134 C-17s replace the 266 C-141s because they will have 

fewer aircraft and less flexibility to respond to multiple theater 

requirements.
Page 36 GAO/NSIAD-00-135 Military Readiness

Appendix III

Aging of the Mobility Aircraft Contributes to 

Lower Mission Capable Rates ApendxiI

Aging is a general factor that affects all weapon systems. Older aircraft and 

engines not only require more inspections and maintenance but also 

increase downtime for maintenance. The aging issue is important to 

mobility air forces since they have some of the oldest aircraft in the Air 

Force fleet. The KC-10 aircraft is relatively young, whereas the KC-135 is 

the oldest aircraft in the fleet and some of the C-5As are not far behind.

According to Air Force officials, one of the reasons for the lower than 

expected mission capable rates in recent years for the C-5 and KC-135 

aircraft is their age. Both the service life (flying hours) and the 

chronological age contribute to structural fatigue, corrosion cracking, 

worn out systems, and obsolescence. Each of these issues causes a large 

workload that directly affects aircraft availability due to increased 

(1) depot maintenance days, (2) field maintenance (inspections and repair), 

and (3) operational restrictions.

Age of Mobility Aircraft 

Is High

The C-5 fleet has two primary models, the C-5A and the C-5B. The 76 C-5As 

range from 24 to 30 years old, with an average of 27.6 years, and the 

50 C-5Bs range from 10 to 13 years old and average 11.5 years (see fig.13). 

Together, they average about 21 years old.
Appendix III

Aging of the Mobility Aircraft Contributes to 

Lower Mission Capable Rates

Page 37 GAO/NSIAD-00-135 Military Readiness

Figure 13: Age of the C-5 Fleet as of December 1999

Source: Warner Robins Air Logistics Center, Robins Air Force Base, Ga. 

The 546 KC-135s are the oldest of the Air Force’s air mobility aircraft. These 

aircraft range in age from 35 to 44 years old and average 39 years (see fig. 

14).

Years

10 11 12 13 24 25 26 27 28 29 30

0

5

10

15

20

25 Aircraft

C-5B C-5A
Appendix III

Aging of the Mobility Aircraft Contributes to 

Lower Mission Capable Rates

Page 38 GAO/NSIAD-00-135 Military Readiness

Figure 14: Age of the KC-135 Fleet as of September 1999

Source: Oklahoma City Air Logistics Center, Tinker Air Force Base, Okla. 

The 59 KC-10 aircraft range in age from 12 to 20 years and average over 

15 years old (see fig. 15).

0

20

40

60

80

100

120 Number of aircraft

35 36 37 38 39 40 41 42 43 44

Years
Appendix III

Aging of the Mobility Aircraft Contributes to 

Lower Mission Capable Rates

Page 39 GAO/NSIAD-00-135 Military Readiness

Figure 15: Age of the KC-10 Fleet as of January 2000

Source: Oklahoma City Air Logistics Center, Tinker Air Force Base, Okla.

Depot Maintenance 

Days Are Increasing

While not all of the increases in depot maintenance time may be 

attributable to aircraft age, as the C-5 and KC-135 aircraft have aged, the 

number of days they spend in depot maintenance has increased. The Air 

Mobility Command considers the C-5 depot maintenance time 

unacceptably high. As shown in figure 16, the average depot maintenance 

time for the 76 C-5As has increased from 163 days to 278 days. The 

50 C-5Bs, time in depot has been relatively stable, ranging from 173 days in 

1993 to 172 days in 1997. The KC-135’s average time spent in depot 

maintenance was 374 days in 1999, up from an average of 170 days in 1992 

(see fig. 17).

0

2

4

6

8

10

12

Number of aircraft

12 13 14 15 16 17 20

Years
Appendix III

Aging of the Mobility Aircraft Contributes to 

Lower Mission Capable Rates

Page 40 GAO/NSIAD-00-135 Military Readiness

Figure 16: C-5 Average Depot Maintenance Days Fiscal Years 1989-99

Source: Warner Robins Air Logistics Center, Robins Air Force Base, Ga.

C-5A

C-5B

data not available data not available

89 90 91 92 93 94 95 96 97 98 99

Year

0

50

100

150

200

250

300

350
Appendix III

Aging of the Mobility Aircraft Contributes to 

Lower Mission Capable Rates

Page 41 GAO/NSIAD-00-135 Military Readiness

Figure 17: KC-135 Average Depot Maintenance Days Fiscal Years 1992−99

Source: Oklahoma City Air Logistics Center, Tinker Air Force Base, Okla.

The reasons for the high depot maintenance for the KC-135 have changed. 

According to project management data, the key maintenance action in 

fiscal year 1998 was to repair the aircraft’s surface. In fiscal year 1999, the 

primary problem appeared to be fixing wing defects.

Number of Days

KC-135

Year

0

50

100

150

200

250

300

350

400

92 93 94 95 96 97 98 99
Page 42 GAO/NSIAD-00-135 Military Readiness

Appendix IV

Not Mission Capable for Supply and 

Cannibalization Rates Generally Exceed Air 

Mobility Command Standards ApendxiIV

The C-5, KC-135, and KC-10 aircraft have experienced higher than expected 

not mission capable for supply (NMCS) rates and/or cannibalization 

(removing parts from one aircraft to fix another) rates during fiscal

years 1997 through 1999 due to a lack of spare parts. 

High NMCS and 

Cannibalization Rates 

Evidence the Lack of 

Spare Parts

Aircraft are classified as NMCS when they cannot perform any missions 

due to the unavailability of parts. According to Air Force officials, the lack 

of aircraft spare parts is a major contributor to the lower than expected 

mission capable rates for the C-5, KC-135, and to a lesser degree KC-10 

aircraft. Particularly with the C-5 and KC-135 aircraft, the NMCS rates have 

exceeded the current Air Mobility Command standard in fiscal years 1997 

through 1999. The cannibalization rates for all three aircraft have generally 

exceeded the current Air Mobility Command standard, which is based on 

frequency per 100 flights or sorties. Cannibalizations usually occur because 

parts are unavailable in the supply system and therefore may have 

minimized the potential NMCS and spare parts shortage.

The C-5 has experienced problems with a lack of spare parts and high 

levels of cannibalizations for the last 3 fiscal years. The lack of spares has 

caused the C-5 fleet to consistently exceed Air Mobility Command’s NMCS 

and cannibalization standards during that period, at times by more than 

250 percent (see figs. 18 and 19).
Appendix IV

Not Mission Capable for Supply and 

Cannibalization Rates Generally Exceed Air 

Mobility Command Standards

Page 43 GAO/NSIAD-00-135 Military Readiness

Figure 18: C-5 NMCS Rates Compared to the Air Mobility Command Standard for Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

C-5 NMCS Rate

C-5 AMC Standard NMCS Rate

96 97 98

Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug

0

5

10

15

20

25
Appendix IV

Not Mission Capable for Supply and 

Cannibalization Rates Generally Exceed Air 

Mobility Command Standards

Page 44 GAO/NSIAD-00-135 Military Readiness

Figure 19: C-5 Cannibalizations per 100 Sorties Compared to the Air Mobility Command Standard for Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

Figure 20 shows that the KC-135 NMCS rates have exceeded the Air 

Mobility Command standard during the last 3 fiscal years and that the rates 

increased significantly at the end of 1999. Air Force officials attribute this 

year-end increase to the failure of the flight control systems in the tail 

section and the lack of available parts for the needed repairs.

C-5 AMC Standard Cannibalization Rate

C-5 Cannibalization Rate

96 97 98

Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug

0

10

20

30

40

50

60

70

80
Appendix IV

Not Mission Capable for Supply and 

Cannibalization Rates Generally Exceed Air 

Mobility Command Standards

Page 45 GAO/NSIAD-00-135 Military Readiness

Figure 20: KC-135 NMCS Rates Compared to the Air Mobility Command Standard for Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

As figure 21 shows, KC-135 cannibalizations during the last 3 fiscal years 

also exceeded the Air Mobility Command standard, at times by as much as 

three times. The high rate of cannibalizations to support mission capability 

levels may have served to minimize the NMCS rate, which already 

exceeded Air Mobility Command standards.

KC-135 NMCS Rate

KC-135 AMC Standard NMCS Rate

96 97 98

Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug

0

5

10

15

20

25

30
Appendix IV

Not Mission Capable for Supply and 

Cannibalization Rates Generally Exceed Air 

Mobility Command Standards

Page 46 GAO/NSIAD-00-135 Military Readiness

Figure 21: KC-135 Cannibalizations Per 100 Sorties Compared to the Air Mobility Command Standard for Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

The KC-10 NMCS rates, as shown in figure 22, were usually below the Air 

Mobility Command standard. However, the cannibalization rates, as shown 

in figure 23, were frequently higher than the standard during the last 3 fiscal 

years. Again, the rate of cannibalizations may have served to minimize the 

KC-10’s NMCS rate.

KC-135 Cannibalization Rate

KC-135 AMC Standard Cannibalization Rate

96 97 98

Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug Oct- Dec Feb Apr Jun Aug

0

2

4

6

8

10

12

14

16
Appendix IV

Not Mission Capable for Supply and 

Cannibalization Rates Generally Exceed Air 

Mobility Command Standards

Page 47 GAO/NSIAD-00-135 Military Readiness

Figure 22: KC-10 NMCS Rates Compared to the Air Mobility Command Standard for Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

0

1

2

3

4

5

6

7

8

9

10

Oct96Nov Dec Jan97Feb Mar Apr May Jun Jul Aug Sep Oct97Nov Dec Jan98Feb Mar Apr May Jun Jul Aug Sep Oct98Nov Dec Jan99Feb Mar Apr May Jun Jul Aug Sep99

Rate in Percent

KC-10 NMCS Rate

KC-10 AMC NMCS Standard
Appendix IV

Not Mission Capable for Supply and 

Cannibalization Rates Generally Exceed Air 

Mobility Command Standards

Page 48 GAO/NSIAD-00-135 Military Readiness

Figure 23: KC-10 Cannibalizations Per 100 Sorties Compared to the Air Mobility Command Standard for Fiscal Years 1997-99

Source: U.S. Air Force, Air Mobility Command.

0

1

2

3

4

5

6

7

Oct96Dec Feb Apr Jun Aug Oct97Dec Feb Apr Jun Aug Oct98Dec Feb Apr Jun Aug

KC-10 AMC Cannibalization Standard

KC-10 Cannibalization Rate
Page 49 GAO/NSIAD-00-135 Military Readiness

Appendix V

Scope and Methodology ApendxiV

To examine the capability of U.S. strategic air mobility forces to execute 

the requirements for winning two nearly simultaneous major theater wars, 

we received briefings, reviewed documents, and interviewed officials at the 

Office of the Secretary of Defense, the Office of the Joint Chiefs of Staff, 

the U.S. Transportation Command, Headquarters, U.S. Air Force, the U.S. 

Air Force Mobility Command, and various other Air Force commands in 

the United States. We also reviewed our prior reports. Much of our analysis 

focused on comparing the wartime strategic airlift and aerial refueling 

requirements identified as a result of the Mobility Requirement Study 

Bottom Up Review Update, and 1996 aerial refueling study to aircraft 

mission capability status in fiscal years 1997, 1998, and 1999.

To identify the C-5, C-141, C-17, KC-135, and KC-10 aircraft mission 

capability status over the 3-year period, we obtained and reviewed 

information from the U.S. Air Force Air Mobility Command’s Health of 

Force database. The Health of Force database reported the monthly 

aircraft mission capability, not mission capable due to supply, and the parts 

cannibalization rates compared to performance standards. To ensure we 

used the appropriate data, we resolved any conflicting information with Air 

Mobility Command officials. We also reviewed data reported by units 

through the Status of Resources and Training System and the Air Force’s 

System Executive Management Reports. We reviewed selected classified 

DOD Joint Monthly Readiness Review Reports and talked with Joint Staff 

officials to obtain information on the impact of airlift and aerial refueling 

shortfalls.

To identify reasons for the airlift and aerial refueling capability shortfalls, 

we talked with and obtained information from officials at Headquarters Air 

Mobility Command, the Headquarters Air National Guard, Headquarters Air 

Force Reserves, and the U.S. Air Force Air Logistics Center project offices 

for the C-5, KC-135, and KC-10. We also received briefings and talked with 

officials from C-5 units at Dover Air Force Base, Delaware.

We obtained and reviewed information on DOD’s efforts to resolve the 

shortfalls and related costs from a variety of sources. We reviewed the 

Joint Staff’s deficiency database to identify concerns raised during the 

Joint Monthly Readiness Reviews that are being tracked until they are 

resolved. We also obtained the cost of DOD’s plans to buy the remaining 

C-17s from its future year defense plan. The C-5 and KC-135 project offices 

and officials at Headquarters Air Mobility Command provided their aircraft 

modernization plans and related costs. Headquarters U.S. Air Force 

identified several initiatives to reduce the spare parts shortfall and the 
Appendix V

Scope and Methodology

Page 50 GAO/NSIAD-00-135 Military Readiness

associated costs. We obtained general funding data from DOD’s future year 

defense plan. We also monitored the status of several studies, including the 

Mobility Requirements Study 2005 that could affect future air mobility 

forces and the budget.

Our review was conducted from July 1999 through April 2000 in 

accordance with generally accepted government auditing standards.
Page 51 GAO/NSIAD-00-135 Military Readiness

Appendix VI

Comments From the Department of Defense ApendxiVI

Note: GAO comments

supplementing those in the 

report text appear at the 

end of this appendix.

See comment 1.
Appendix VI

Comments From the Department of Defense

Page 52 GAO/NSIAD-00-135 Military Readiness

See comment 1.
Appendix VI

Comments From the Department of Defense

Page 53 GAO/NSIAD-00-135 Military Readiness
Appendix VI

Comments From the Department of Defense

Page 54 GAO/NSIAD-00-135 Military Readiness

See comment 2.

See comment 3.
Appendix VI

Comments From the Department of Defense

Page 55 GAO/NSIAD-00-135 Military Readiness

See comment 4.

See comment 5.

See comment 6.

See comment 7.

See comment 8.

See comment 9.
Appendix VI

Comments From the Department of Defense

Page 56 GAO/NSIAD-00-135 Military Readiness

See comment 10.

See comment 11.

See comment 12.

See comment 13.

See comment 14.

See comment 15.

See comment 16.
Appendix VI

Comments From the Department of Defense

Page 57 GAO/NSIAD-00-135 Military Readiness

See comment 17.
Appendix VI

Comments From the Department of Defense

Page 58 GAO/NSIAD-00-135 Military Readiness

The following are GAO’s responses to DOD’s comments dated May 15, 2000.

GAO Comments 1. With respect to whether DOD has sufficient airlift and air refueling 

capability to meet the two major theater war requirements, we believe 

our data show that due to the substandard mission capable status of the 

fleet, the airlift and aerial refueling capabilities available for the onset 

of war are significantly below the Air Mobility Command’s wartime 

planning requirements. To calculate our aircraft mission capable rates, 

we compared the number of mission capable aircraft to the total 

number of aircraft that should be mission available according to the 

Command’s wartime planning process (total aircraft minus those 

allotted for training and depot maintenance). This method for 

calculating mission capable rates is consistent with Air Force Pamphlet 

10-1403, “Air Mobility Planning Factors” and recommended in DOD’s 

October 1999 guidance for future Quarterly Readiness Reports to the 

Congress. In contrast, the Air Mobility Command rates referred to by 

DOD compared the number of mission capable aircraft to the total 

number of aircraft physically at units. This methodology results in 

higher mission capable rates because unit totals do not account for 

their aircraft that are in depot in excess of those allotted for 

maintenance.

2. According to the DOD Quarterly Readiness Reports to the Congress, 

the low mission capable status of air mobility forces, while not 

jeopardizing our ability to win the war, add risk and would delay the 

implementation of war plans. Furthermore, it states that potentially 

longer timelines required to halt the enemy and start a counter 

offensive increase the potential for higher casualties in the interim and 

during the warfight.

3. We agree that these plans could allow DOD to increase airlift capability 

from 46 MTM/D in 1999 to 50 MTM/D in 2005 when delivery of 120 C-17s 

is completed, assuming they achieve the 87.5-percent wartime mission 

capable rates. We included DOD’s comments on the purposes of the 

$18-billion investment in table 5.

4. We do not believe table 1 is misleading. The Air Mobility Command’s 

wartime planning process shows that of the 50 MTM/D, a portion of the 

29.2-MTM/D military airlift requirement is to be delivered by each type 

of aircraft as shown in table 1. The Air Mobility Command also specifies 

expected mission capable rates by type of refueling aircraft. MPF/D is 
Appendix VI

Comments From the Department of Defense

Page 59 GAO/NSIAD-00-135 Military Readiness

cited as another aerial refueling metric in the Air Mobility Strategic 

Plan 2000.

5. The footnote is changed to reflect DOD’s comment.

6. We did not change the footnote. The Air Mobility Command provided 

the definition cited.

7. The paragraph is changed to reflect DOD’s comment.

8. The paragraph is changed to reflect DOD’s comment.

9. The paragraph is changed to reflect DOD’s comment.

10. See our response to comment 1.

11. The paragraph is changed to reflect DOD’s comment.

12. The paragraph is changed to reflect DOD’s comment.

13. The number is changed to reflect DOD’s comment.

14. We did not agree with DOD’s comment. The risk of a shortfall remains 

until aircraft achieve standard mission capable rates and efforts to 

drive down the number of aircraft in depot are successful.

15. The paragraph is changed to reflect DOD’s comment.

16. We do not believe it is necessary to specify the name of the part.

17. The number is changed to reflect DOD’s comment.
Page 60 GAO/NSIAD-00-135 Military Readiness

Appendix VII

GAO Contacts and Staff Acknowledgments ApendxiVI

GAO Contacts William C. Meredith (202) 512-4275

Richard G. Payne (757) 552-8119

Staff 

Acknowledgments

In addition to those named above, Raul S. Cajulis, Lawrence E. Dixon, 

James E. Lewis, Sharon L. Reid, and Gregory J. Symons made key 

contributions to this report.

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