United States General Accounting Office

GAO Report to Congressional Committees

August 1996 U.S. COMBAT AIR

POWER

Aging Refueling

Aircraft Are Costly to

Maintain and Operate

G O A

years

1921 - 1996

GAO/NSIAD-96-160

GAO United States

General Accounting Office

Washington, D.C. 20548

National Security and

International Affairs Division

B-272009 

August 8, 1996

Congressional Committees

Due to the changing nature of defense operations, the demands on the services’ air refueling

fleet have not diminished since Operation Desert Storm. However, the Air Force’s principal

tanker aircraft—the KC-135s—are 30 to 40 years old and, as a result, are taking progressively

more time and money to maintain and operate. Nevertheless, the Air Force has no immediate

plans to replace the KC-135s as it currently considers the replacement of other aircraft a higher

priority. Additionally, because of the demands on the tanker fleet, Air Force active and reserve

air refueling personnel have been stressed to satisfy mission needs.

We examined the services’ air refueling needs, the cost to operate and maintain the air refueling

fleet, and the impact that the air refueling missions have on the active and reserve forces. This

report contains a recommendation to the Secretary of Defense concerning future aircraft

procurement that provides an opportunity to enhance operational flexibility by acquiring a

dual-use aircraft that combines airlift and refueling capabilities.

This report was part of our broader effort to assess how the Department of Defense might

better adapt its combat air power to meet future needs. We are addressing this report to you

because of your responsibility for the issues discussed and your interest in the subject.

Please contact me at 202-512-3504 if you or your staff have any questions concerning this report.

Major contributors to this report are listed in appendix IV.

Richard Davis

Director, National Security

 Analysis
B-272009 

List of Congressional Committees

The Honorable Strom Thurmond

Chairman

The Honorable Sam Nunn

Ranking Minority Member

Committee on Armed Services

United States Senate

The Honorable Ted Stevens

Chairman

The Honorable Daniel K. Inouye

Ranking Minority Member

Subcommittee on Defense

Committee on Appropriations

United States Senate

The Honorable Floyd Spence

Chairman

The Honorable Ronald V. Dellums

Ranking Minority Member

Committee on National Security

House of Representatives

The Honorable C.W. Bill Young

Chairman

The Honorable John P. Murtha

Ranking Minority Member

Subcommittee on National Security

Committee on Appropriations

House of Representatives

Page 2 GAO/NSIAD-96-160 U.S. Combat Air Power
B-272009 

Page 3 GAO/NSIAD-96-160 U.S. Combat Air Power
Executive Summary

Purpose Air refueling extends the operational range of the military services’

aircraft, increases combat capabilities, and enhances commanders’

flexibility in the use of aircraft. During Operation Desert Storm, the Air

Force routinely refueled Navy, Marine Corps, allied, and its own aircraft.

Since then, because of contingency and other operations, the demands on

the tanker fleet have not diminished, even though the services have

downsized in many other areas. During this review, GAO examined the

services’ air refueling needs, the cost to operate and maintain the air

refueling fleet, and the impact that the air refueling missions have on the

active and reserve forces. This report is one of a series of reports assessing

how the Department of Defense (DOD) might better adapt its combat air

power to meet future needs. Other reports in this series address close fire

support, interdiction, air superiority, suppression of enemy air defense,

and surveillance and reconnaissance.

Background The Air Force, Navy, and Marine Corps operate almost 900 tanker aircraft,

most of which are derivatives of cargo or commercial aircraft. The Air

Force owns about 690 of them, divided nearly equally between active and

reserve forces. The Air Force’s KC-135 fleet of about 550 aircraft refuels

Navy, Marine Corps, and Air Force combat aircraft, strategic bombers,

command and control aircraft, and airlift aircraft. The Navy’s S-3 refuels

Navy and Marine Corps aircraft during their launch from and recovery

aboard aircraft carriers, and the Marine Corps’ KC-130 refuels Marine

fighters and helicopters. The U.S. Air Force Special Operations Command

refuels special operations helicopters with its HC-130s and MC-130s.

Tanker aircraft also airlift passengers and cargo. Over the next 6 years, the

services estimate they will spend about $2.4 billion a year to operate these

aircraft.

Results in Brief Although the services’ air refueling tanker aircraft meet current needs,

satisfying future requirements may be difficult. The long-term

serviceability of the KC-135 tanker fleet is questionable, because the

aircraft are 30 to 40 years old and, as a result, are taking progressively

more time and money to maintain and operate. Furthermore, the Air Force

could spend over $6 billion in modifications and structural repairs to keep

the KC-135 fleet operational. Even though the Air Mobility Command

doubts that the KC-135 can be economically operated beyond 2020, it does

not plan to begin to replace them until around 2013, which is 6 years later

than planned a year ago. The Command deferred the replacement program

because it considers replacement of the C-5A transport beginning in 2007 a

Page 4 GAO/NSIAD-96-160 U.S. Combat Air Power
Executive Summary

higher priority. However, the Air Force must eventually replace the

KC-135. As the Air Force makes plans for replacing its C-5A, it has an

opportunity to enhance operational flexibility by acquiring a dual-use

aircraft that combines airlift and refueling capabilities. Current tankers

have demonstrated the versatility and value of a dual-use aircraft. For

example, the KC-10, a derivative of the commercial DC-10, was acquired as

a dual-role aircraft and the KC-135 is increasingly used to transport

high-priority cargo and passengers. The Air Force now plans to buy both a

new transport aircraft to replace its C-5A plus a new tanker later to

replace the KC-135. Since tanker aircraft are frequently used as cargo

aircraft, a dual-use aircraft is a viable option.

In recent years, Air Force active and reserve air refueling personnel have

been stressed to satisfy mission needs. As a result, active duty tanker

crews have approached the Air Force Chief of Staff’s management limit

that active duty crews should not be away from their home bases on

temporary assignments more than 120 days a year. In fiscal years 1994 and

1995, the deployment rates for individual tanker crew positions,

particularly navigators, approached the 120-day management limit, ranging

from 103 to 117 days, depending on crew position. To stay below the

120-day limit and relieve pressure on active duty tanker crews, the Air

Force has looked to the air reserve units to take on more of the tanker

workload in a role not originally envisioned for reserve forces. Air Reserve

Components flew 27 percent of the total sorties and 30 percent of the total

flying hours flown by the Air Mobility Command and the Air Reserve

Components during fiscal year 1993. This increased in fiscal year 1995 to

44 percent of the sorties and 49 percent of the flying hours flown by the

Air Mobility Command and the Air Reserve Components. Currently, the

reserve force can maintain this level of operations because many crew

members volunteer extra time, thus exceeding the reserves’ legal training

requirement of 38 days a year. Many, in fact, have served over 100 days a

year for training and flying sorties. This effort is in addition to maintaining

their civilian jobs. According to service officials, these units are now

operating at about 95 percent of their potential availability.

Principal Findings

The Aging Tanker Force Is

More Difficult to Maintain

The KC-135 tankers, many of which are 40 years old, are the oldest aircraft

the services operate and are becoming more expensive to operate 

Page 5 GAO/NSIAD-96-160 U.S. Combat Air Power
Executive Summary

(the cost per KC-135 flying hour is projected to increase from $8,662 in

1996 to $10,761 in 2001). The military has little or no experience operating

and maintaining aircraft of this age, and there are no commercial airline

fleets of a comparable age. Consequently, the Air Force only recently

began to collect data to enable it to predict how long or effectively these

aircraft can continue to operate.

As the KC-135 tankers age, they require more maintenance, reducing the

number of aircraft available for operations. For example, between fiscal

years 1991 and 1995, the labor hours planned to complete depot overhauls

of the KC-135s increased by about 36 percent and the average time the

aircraft spent in the depot increased from 158 days to 245 days. According

to Air Force officials, the growth in planned work included time to apply

corrosion preventive compounds and rewire significant portions of each

aircraft. In addition, shortages of spare parts, that were no longer in

production or stocked, and unplanned work, required to correct structural

corrosion and fatigue, contributed to maintenance delays and reduced

aircraft availability.

The Air Force could spend over $6 billion for a variety of modifications

and structural repairs to improve the reliability, maintainability, and

capability of its KC-135s. These include re-engining KC-135Es, replacing

major structural components because of their age or susceptibility to

stress corrosion, adding a multipoint refueling capability to some of the

aircraft, relocating the navigator’s instruments to the pilot and copilot

positions, installing improved compass and radar systems, installing a

global positioning system, and adding a ground collision avoidance

system. Of these potential modifications and repairs, the Air Force has

funded about $390 million for relocating the navigator’s instruments and

installing the global positioning system and the improved compasses and

radars. According to Air Force officials, these modifications and repairs

should reduce maintenance costs and increase the aircraft’s capability.

The Air Force has also funded a $204 million program to modify about

45 KC-135 tankers with a multipoint capability to enhance their ability to

refuel Navy and Marine aircraft. The Desert Storm air campaign and other

operations illustrated both the feasibility and necessity of cross-service air

refueling operations. For example, during Operation Desert Storm, Air

Force tankers supported Navy, Marine Corps, allied, and their own

aircraft. However, adapters had to be installed on the Air Force tankers in

order to refuel Navy, Marine Corps, and allied aircraft. This complicated

joint mission planning because properly configured tankers had to be

available to fill each service’s special needs.

Page 6 GAO/NSIAD-96-160 U.S. Combat Air Power
Executive Summary

Though currently unfunded, the Air Force may also need up to

$600 million to overhaul or upgrade about 600 engines for the KC-135s.

Even when overhauled, however, these engines will not meet Federal

Aviation Administration and international noise and air pollution

standards that become effective by 2000. As a result, the aircraft may not

be allowed to operate from some airfields, or their operations may be

restricted.

Aging Tanker and Airlifter

Forces Provide an

Opportunity to Acquire a

Dual-Use Aircraft

Even though the Air Mobility Command has delayed consideration of a

replacement of the KC-135 from fiscal year 2007 to 2013 while accelerating

the replacement of the C-5A transport aircraft beginning in 2007, the aging

KC-135 tankers must ultimately be replaced.1

 The anticipated acquisition

of a C-5A replacement aircraft may provide an excellent opportunity to

satisfy both airlift and tanker needs. Current tankers have demonstrated

the versatility and value of a dual-use, airlift-tanker aircraft. For example,

the KC-10, a derivative of the commercial DC-10, was acquired as a

dual-role aircraft. It demonstrated the viability of that concept during

Desert Shield/Storm during which it off-loaded almost 300 million pounds

of fuel (about 25 percent of the total) and transported about 54 million

pounds of cargo and about 6,700 passengers. Similarly, the KC-135 is

increasingly used to transport high-priority cargo and passengers. The Air

Mobility Command allocates 26 of these aircraft to wartime airlift tasks. In

addition, some foreign nations have converted commercial aircraft built by

U.S. companies to provide air refueling capabilities for their military

aircraft.

Peacetime Activities Have

Increased Demands on the

Tanker Crews

The relocation of U.S. forces from overseas bases to the United States and

the increasing U.S. involvement in contingency and other peacetime

missions have increased the demands for air refueling. While the number

of tactical aircraft needing refueling is declining, as is much of the military

force, tanker support is increasingly required. The drawdown of U.S.

forces from overseas bases has added to refueling requirements because

of the need to refuel U.S.-based tactical aircraft, enabling them to reach

and return from their overseas destinations and to facilitate their

performance and sustainment once they are in place. As a result, active

duty tanker crews have spent nearly 120 days a year on temporary

assignments away from their home bases. The Air Force Chief of Staff’s

1

The Air Force does not plan to replace the KC-135 at this time because, it says, it cannot afford to

simultaneously acquire a replacement tanker, the C-17, a replacement for the C-5A transport aircraft,

and a new tactical aircraft such as the F-22.

Page 7 GAO/NSIAD-96-160 U.S. Combat Air Power
Executive Summary

management limit is that its members not spend more than 120 days a year

on temporary assignments.

To stay below the 120-day temporary duty level and relieve pressure on

active duty tanker crews, air reserve units, which currently maintain more

than half of the KC-135 fleet, have taken on more of the tanker workload in

a role that was not originally envisioned for the Air Reserve Component.

As a force originally intended to augment the active Air Force in time of

war or national emergency, Air Reserve Component personnel are legally

required to serve 38 days a year for training in peacetime: one weekend a

month and 2 weeks of annual active duty for training. However, Air

Reserve Components flew 27 percent of the total sorties and 30 percent of

the total flying hours flown by the Air Mobility Command and the Air

Reserve Components during fiscal year 1993. This increased in fiscal year

1995 to 44 percent of the sorties and 49 percent of the flying hours.

According to senior officials, the Air Reserve Component units are now

operating at about 95 percent of their potential availability. While reserve

crew members cannot be required to serve more than 38 days a year, many

volunteer extra time. According to Air Force Reserve officials’ data, many

crew members, in addition to meeting the demands of their families and

their civilian employers, averaged more than 100 days a year supporting

their units’ training requirements and air refueling sorties. Thus, the Air

Force is able to support peacetime tanking requirements in large part

because of the high tempo of active forces and the volunteerism in the

Reserve Components.

Recommendation Because the services have successfully used dual-role aircraft for both air

refueling and airlift missions, GAO believes that a dual-use replacement

aircraft could fulfill both airlift and air refueling missions. Accordingly,

GAO recommends that the Secretary of Defense require that future studies

and analyses of replacement airlift and tanker aircraft encompass both

mission areas, with the goal to identify the optimum size, mix, and time to

procure a multimission aircraft that, when combined with C-5Bs, C-17s,

and KC-10s, will meet those requirements. Such an aircraft would

eliminate the need to acquire two aircraft types, one for airlift and the

other for refueling.

Agency Comments In its comments on a draft of this report, DOD wrote that the report

accurately portrays some of the challenges facing the KC-135 fleet in the

coming years. It also said that it believes the current force structure can

Page 8 GAO/NSIAD-96-160 U.S. Combat Air Power
Executive Summary

adequately meet requirements for the foreseeable future and agreed that

future studies and analysis of replacing refueling and airlift aircraft should

include an analysis of using one aircraft to accomplish both missions. It

acknowledged that it was successful in using a single aircraft, such as the

KC-135 for both airlift and refueling. However, DOD said that it could not

commit to a dual-use replacement aircraft until a study including

operational issues is completed. GAO agrees that such analysis should be

conducted before a decision is made. DOD did not comment on the stress

of peacetime activities on tanker crews in its written response. (See

app. I.)

Page 9 GAO/NSIAD-96-160 U.S. Combat Air Power
Contents

Executive Summary 4

Chapter 1 

Introduction

12

The Current Tanker Fleet 12

Tankers’ Evolving Support Role 13

Tanker Costs 16

Objectives, Scope, and Methodology 17

Chapter 2 

The Services Have

Deferred Plans to

Replace Aging Tanker

Aircraft

19

Tanker Fleet Meets Current Needs 19

Expense and Time to Maintain Aging Tankers Have Increased 22

Costs to Modify KC-135s Could Be Substantial 27

DOD Could Enhance Operational Flexibility With a Dual-Role

Tanker/Cargo Aircraft

29

Conclusion 32

Recommendation 32

Agency Comments 33

Chapter 3 

Peacetime Activities

Are Stressing the

Tanker Fleet’s

Support Capabilities

34

Increased Peacetime Activity Results in High Deployment Rates

for the Active Force

34

Reserve Component Is Performing More Refueling Missions 37

Officials Say Active and Reserve Assignment Mix Needs

Reevaluation

38

Conclusion 39

Appendixes Appendix I: Comments From the Department of Defense 40

Appendix II: Air Force and Navy Air Refueling Systems 42

Appendix III: Locations Visited 43

Appendix IV: Major Contributors to This Report 45

Tables Table 1.1: Services’ Tanker Aircraft and the Aircraft They Support 12

Table 1.2: Funding for the Services’ Tankers 17

Table 2.1: Age of the Services’ Tanker Aircraft 20

Table 2.2: Possible KC-135 Modifications 27

Figures Figure 1.1: Air Force KC-135 Refueling a KC-10 14

Figure 1.2: Air Force KC-135 Refueling an F-16 15

Figure 1.3: HC-130 Refueling an HH-53 16

Page 10 GAO/NSIAD-96-160 U.S. Combat Air Power
Contents

Figure 2.1: Aircraft Ages 21

Figure 2.2: Increase in KC-135 Depot Overhaul Time 24

Figure 2.3: KC-135/Replacement Tanker Force Mix 31

Figure 3.1: KC-135 Flying Hours in Overseas Commands 36

Abbreviations

AFRES Air Force Reserve

AMC Air Mobility Command

ANG Air National Guard

ARC Air Reserve Component

DOD Department of Defense

FYDP Future Years Defense Program

Page 11 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 1 

Introduction

The Air Force, Navy, and Marine Corps tankers provide refueling support

to both land- and carrier-based aircraft. Tankers extend the operational

range of aircraft, enable aircraft to carry larger loads, increase combat

tempos, and enhance commanders’ flexibility. As world conditions have

changed, so has the role of the tanker. While the Air Force’s tankers were

once principally intended to support strategic bombers, the tanker fleet is

now responsible for various air refueling tasks in support of both peace

and wartime missions. Although each service has its own specific air

refueling needs, cross-service refueling operations have become

increasingly important, as illustrated in Operation Desert Storm when Air

Force tankers routinely refueled Navy, Marine Corps, and allied aircraft in

addition to its own. Tankers also carry passengers and cargo. The cost to

operate the tanker fleet will average about $2.4 billion a year between

fiscal years 1996 and 2001.

The Current Tanker

Fleet

The Air Force, Navy, and Marine Corps currently operate almost 900

tanker aircraft (see table 1.1). The Air Force owns about 690 tankers, or

about 78 percent of the entire fleet, and is primarily responsible for

land-based peacetime and wartime refueling operations. Before Operation

Desert Storm, most of the Air Force tanker fleet was in the active force.

Today, however, about 50 percent of the overall Air Force tanker fleet is

operated by the reserve forces.1

Table 1.1: Services’ Tanker Aircraft

and the Aircraft They Support Service Model Quantity Aircraft supported

Air Force

HC-130 67 Special Operations Command helicopters

KC-10 59 Tactical aircraft/strategic

bombers/transports

MC-130 14 Special Operations Command helicopters

KC-135 552 Tactical aircraft/strategic

bombers/transports

Marine Corps

KC-130 74 USMC helicopters/tactical aircraft

Navy

S-3 118 Carrier-based tactical aircraft

Total 884

1

As discussed in ch. 3, the reserve forces operate 54 percent of the KC-135s.

Page 12 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 1 

Introduction

Tankers’ Evolving

Support Role

The current tanker fleet has evolved from post-World War II requirements

to contain Soviet military power. During the Cold War era, the role of the

KC-135 was to refuel strategic bombers that would carry out the strategic

nuclear war plan. Support of the plan remained the KC-135s’ primary

mission until the demise of the Soviet Union and the resultant reduction in

the strategic threat. Tankers were also used to support tactical operations:

first during the Vietnam conflict and later during Operations Desert Shield

and Desert Storm. As the threat changed, so did the role of the tanker.

Today, under the Department of Defense’s (DOD) Planning Guidance, the

KC-10/KC-135 fleet is required to support operations in response to major

regional conflicts and the strategic nuclear war plan. However, tankers are

increasingly being tasked to support contingency and other missions as

both tanker and cargo aircraft.

Refueling Tasks Refueling aircraft as they deploy to and operate from overseas locations is

one of the major tasks of the tanker fleet. In-flight refueling allows tactical

and airlift aircraft to travel longer distances with large cargo and

passenger loads and also reduces the need for access to overseas bases,

thus minimizing potential impediments to the movement of U.S. forces

throughout the world. Because they can be refueled in the air, combat air

forces within a theater can strike longer range targets or carry larger

weapons loads than their normal fuel/weapons loads would permit and

can remain airborne for longer periods of time. (Fig. 1.1 shows an Air

Force KC-135 refueling a KC-10.)

Page 13 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 1 

Introduction

Figure 1.1: Air Force KC-135 Refueling

a KC-10

Source: DOD.

Because of the return of U.S. forces from overseas, as bases were closed

due to downsizing, tankers are refueling more aircraft as they deploy to

and operate from distant trouble spots. The reduced size of the U.S. force

has made it necessary to rely more on joint operations involving mixed

groups of U.S. Air Force, Navy, Marine Corps, and allied aircraft to

capitalize on the unique strengths of each service. For example, during

Operations Desert Shield and Storm, Air Force tankers transferred about

14 percent of 1.2 billion pounds of fuel to Navy and Marine Corps aircraft

and about 2 percent to allied aircraft.2

 (Fig. 1.2 shows refueling in flight.)

2

Allied aircraft were from Bahrain, Canada, Italy, Oman, Saudi Arabia, and the United Arab Emirates.

Page 14 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 1 

Introduction

Figure 1.2: Air Force KC-135 Refueling

an F-16

Source: Air National Guard.

Each service has other, specific refueling requirements. Air Force tankers

are tasked to refuel strategic nuclear bombers, command and control

aircraft, and combat search and rescue helicopters. The Air Force Special

Operations Command also uses tankers to refuel both Air Force and Army

special operations helicopters. Navy tankers support carrier-based aircraft

and are critical to their safe recovery since alternate airfields are

frequently not available. Marine Corps tankers support fighters and

helicopters involved in expeditionary and crisis response operations.

(Fig. 1.3 shows an Air Force HC-130 refueling a search and rescue

helicopter.)

Page 15 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 1 

Introduction

Figure 1.3: HC-130 Refueling an HH-53

Source: DOD.

Airlift Tasks In addition to refueling missions, several types of tanker aircraft play

significant roles in airlifting passengers and cargo. For example, to meet

wartime requirements, the Air Mobility Command’s (AMC) 1996 master plan

allocates 37 KC-10s to airlift tasks and only 15 to air refueling. The nine

remaining aircraft are for backup and training. In addition, the Air Force

has increased its use of KC-135s to move high-priority cargo and

passengers, allowing airlifters such as the C-141 to be dedicated to the

tasks only they can accomplish. Between fiscal years 1993 and 1994, active

Air Force KC-135 cargo flights increased about 47 percent. Through fiscal

year 1995, the Air Force bought 150 roller kits to enhance loading and

unloading cargo from the KC-135.3

 The master plan designates 26 KC-135s

for wartime airlift requirements. Marine Corps KC-130s are also frequently

used to transport passengers and cargo. For example, during Operation

Desert Storm, KC-130s airlifted over 3,000 passengers and 8.1 million

pounds of cargo.

Tanker Costs Between fiscal years 1996 and 2001, the services’ estimated annual

operating costs for tankers are about $2.4 billion. Personnel costs account

3

Because the KC-135 was designed as a tanker, it does not have rollers built into its floor as cargo

aircraft do. The roller kits can be moved to KC-135s as they are needed for cargo missions.

Page 16 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 1 

Introduction

for about 32 to 34 percent of costs, while operations and maintenance

costs range from 55 to 61 percent. (See table 1.2)

Table 1.2: Funding for the Services’

Tankers (fiscal year 1994-2001)

Fiscal year

Dollars in thousands

Appropriation 1994 1995 1996-2001a

Aircraft procurement $114,418 $188,257 $1,281,823

Military construction 9,000 55,550 103,334

Military personnel 451,865 794,420 4,778,165

Operations and maintenance 1,194,893 1,431,964 8,484,022

RDT&Eb 11,540 23,006 13,520

Total $1,781,716 $2,493,197 $14,660,864

Note: Funding is based on the 1996 Future Years Defense Program (FYDP), which covers funding

for the Air Force’s KC-10s and KC-135s, all Navy S-3 missions, and the Marine Corps’ KC-130s.

The table does not include funding for the Air Force’s H/MC-130 aircraft because they are not

separately identified in the FYDP.

aTotal for 6 years.

bRDT&E is research, development, testing, and evaluation.

Objectives, Scope,

and Methodology

During this review, we examined the services’ air refueling needs, the cost

to operate and maintain the air refueling fleet, and the impact that the air

refueling missions have on the active and reserve forces. This report is one

of a series of reports assessing how DOD might better adapt its combat air

power to meet future needs. Other reports in this series address close fire

support, interdiction, air superiority, suppression of enemy air defense,

and surveillance and reconnaissance.

To accomplish our objectives, we met with agency officials responsible for

program management and obtained pertinent documents concerning the

characteristics, missions, requirements, employment concepts, and

associated costs of the tanker aircraft. We did not independently

determine the reliability of the cost information. We also obtained

information concerning the maintenance of and planned modifications to

existing systems. We reviewed several studies and reports addressing

these topics. In addition, we discussed air refueling issues with

representatives of several research organizations and defense-related

companies. When analyzing the problems of maintaining aging aircraft, we

concentrated on the Air Force’s KC-135 because it makes up about

two-thirds of the DOD’s tanker inventory.

Page 17 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 1 

Introduction

To gain the operators’ perspective of air refueling operations and

requirements, we met with officials of three unified commands, various

Navy and Air Force commands, and several tanker units. (See app. II for a

list of locations we visited during our review.) During those visits, we

discussed the commands’ policies and procedures for using air refueling

assets. We also observed flight and air refueling operations at several units

and commands. We observed carrier flight operations aboard the U.S.S.

Theodore Roosevelt during its predeployment training and discussed air

refueling issues with air wing personnel. During Joint Training

Exercise 95-2, we visited the Joint Force Air Component Commander

aboard the U.S.S. Mount Whitney and observed how tanker use was

integrated into the air tasking order planning process. During the exercise,

we also visited the U.S.S. Theodore Roosevelt and accompanied the crew

of a KC-135R from the 72d Air Refueling Squadron on a refueling mission

to observe how those plans were executed. To gain a Special Operations

Command perspective, we accompanied the crew of an HC-130 of the 9th

Special Operations Squadron on a night helicopter refueling mission. We

also accompanied the crew of a KC-135E of the 108th Air Refueling Wing

on a refueling flight.

We performed our work from June 1994 to February 1996 in accordance

with generally accepted government auditing standards.

Page 18 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

Although the services’ tankers meet current Defense Planning Guidance

requirements, meeting future requirements may be difficult. Most tankers,

including all Air Force KC-135s, are 30 to 40 years old, and are increasingly

more expensive and time-consuming to support. According to the Air

Force, the cost per KC-135 flying hour is projected to increase by about

24 percent, from about $8,700 in 1996 to $10,800 in 2001. In addition, from

fiscal year 1991 to fiscal year 1995, the average time KC-135s spent in the

depot for scheduled maintenance increased from 158 days to 245 days.

Furthermore, the Air Force may spend over $6 billion in the coming years

to sustain the KC-135 fleet and improve reliability and capability. Despite

the fact that costs to maintain and operate the KC-135s have increased and

its availability has decreased, the Air Force has not estimated the KC-135’s

economic service life and determined when to begin replacing it.

Nevertheless, AMC has delayed consideration of a tanker replacement from

fiscal year 2007 to fiscal year 2013.

Tanker Fleet Meets

Current Needs

According to recent Air Force and other studies, the current KC-10/KC-135

force is generally adequate to meet the requirement to support operations

in response to major regional conflicts and the strategic nuclear war plan.

This determination is based on the Defense Planning Guidance and

current planning assumptions such as the number and types of aircraft to

be supported, the arrival time of forces in the theater, the duration and

nature of the operations, and the availability of air bases. According to Air

Force officials, changes in any of these assumptions impact the tanker

requirement. For example, the tanker requirement would increase

significantly if U.S. forces were denied access to certain overseas air bases

that are critical to supporting the deployment of U.S. forces. Conversely,

requirements would decrease if the time frames for deployment were

lengthened. In a recent study of tanker requirements, the Institute for

Defense Analysis also noted that tanker requirements are very sensitive to

variations in those types of factors.

However, because of the tankers’ age, the services’ ability to meet

requirements over the long term may be a challenge. As table 2.1 shows,

many of the tanker aircraft entered service in the 1960s and 1970s and, in

the case of the KC-135, as long ago as the mid-1950s.

Page 19 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

Table 2.1: Age of the Services’ Tanker

Aircraft Aircraft Service Age (years)

H/MC-130 Air Force 27 to 32

KC-10 Air Force 6 to 15

KC-135 Air Force 31 to 39

KC-130 Marine Corps 18 to 36a

S-3 Navy 18 to 22

aKC-130s have been purchased more recently for the Marine Corps Reserve squadrons.

Source: GAO analysis of service data.

Compared to commercial aircraft, most military tankers are considerably

older. As figure 2.1 shows, only about 4 percent of U.S. commercial

aircraft will be 25 years or older by 2000, whereas all of the Air Force’s

KC-135s are already older, and by 2000, they will be 35 to 43 years old.

Page 20 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

Figure 2.1: Aircraft Ages (year 2000)

<5 5-10 10-15 15-20 20-25 >25

0

20

40

60

80

100

120

Age range (in years)

Percent of fleet

Commercial KC-130 KC-135

Source: GAO analysis of Air Force data.

The Air Force has initiated a program that it hopes will enable it to

determine the effects of corrosion on KC-135 structural life and estimate

the aircraft’s remaining economic service life. The Boeing Company,

manufacturer of the KC-135, projected that the aircraft could fly for many

years beyond the turn of the century, based on the average hours flown,

and a projected utilization of about 300 hours a year per aircraft. This

Page 21 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

projection, however, does not consider the effects of corrosion,

widespread fatigue damage, and stress corrosion cracking on structural

life, which can require major structural modifications and parts

replacement.

In the commercial sector, aircraft are generally considered old when they

reach the end of their economic design life—that lifespan over which their

designers originally believed they could be operated economically.

Economic life, which varies among different aircraft types, has generally

been stated in terms of years in service, number of takeoffs and landings,

and operating hours. Historically, when commercial aircraft reached the

upper limit of one of these measures, they would have most likely been

retired, generally before suffering the damaging effects of corrosion,

incurring higher operating costs, and requiring increased maintenance. In

recent years, however, air carriers have tended to keep older aircraft in

service even though more time and money is needed to maintain them, in

part to meet increased demands for air travel.

Expense and Time to

Maintain Aging

Tankers Have

Increased

As shown in chapter 1, the costs to operate, support, and modernize DOD’s

tanker aircraft are projected at about $2.5 billion annually through 2001.

The Air Force estimates that it will spend about $8.2 billion just for KC-135

direct operations and support during fiscal years 1997-2001. Because the

KC-135s are older, they require more maintenance and longer stays in the

depot during overhaul. As a result, fewer aircraft are available to the

squadrons.

Increase in KC-135

Operating and Support

Costs

According to an Air Force automated budget system, the cost per KC-135

flying hour is projected to increase by about 24 percent, from $8,662 in

1996 to $10,761 in 2001. Increased projected costs of people, fuel, and

depot maintenance are the primary reasons for the higher cost per flight

hour. Costs for personnel are projected to increase by about 12 percent,

for fuel by 17 percent, and for depot maintenance by 60 percent.

Increase in Time and Costs

for Maintenance

The Air Force’s goal to complete KC-135 depot overhauls is 153 calendar

days. However, the actual time that KC-135s spent in the depot for

maintenance increased significantly during the past 4 years. In fiscal 

year 1991, KC-135s spent an average of 158 days in the depot; by fiscal

year 1995, that average had increased over 50 percent, to 245 days.

Numerous aircraft have been in the depot for hundreds of days. For

Page 22 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

example, the percentage of KC-135s spending over 300 days in the depot

grew significantly during this period, from 6.6 percent of aircraft inducted 

(7 of 106) in fiscal year 1991 to 21.2 percent (24 of 113) in fiscal year 1995.

In addition, the number of aircraft exceeding the 153-day turnaround time

goal has increased dramatically from 30 percent of the aircraft inducted in

fiscal year 1991 to 97 percent in fiscal year 1995. Figure 2.2 shows the

growth in the number of aircraft that have exceeded the 153-day goal

between fiscal years 1991 and 1995.

Page 23 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

Figure 2.2: Increase in KC-135 Depot Overhaul Time

1991 1992 1993 1994 1995

0

20

40

60

80

100

120

140

Fiscal year

Number of aircraft

Inducted for overhaul Over 153 days

Source: GAO analysis of Air Force data.

The Air Force cited the age of the aircraft and a lack of replacement parts

as primary reasons for the increased maintenance time. Other contributing

Page 24 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

factors included the lack of information about the condition of aircraft

coming into the depot, and additional work required to detect, repair, and

prevent corrosion. The Air Force indicated that, although the KC-135

design was considered state-of-the-art in the 1950s, design features of the

aircraft make it vulnerable to corrosion damage. For example, when the

planes were built, sealant was not applied between overlapping surfaces

throughout the aircraft, and materials now considered susceptible to

corrosion and stress corrosion cracking were used in the aircrafts’

construction.

KC-135 depot maintenance time is significantly greater than that

experienced by commercial airline fleets during their periodic heavy

maintenance work, referred to as D checks, which most closely represents

Air Force depot maintenance. We previously reported that D checks are

performed every 3 to 9 years, and the maintenance time required ranges

from 10 to 60 days, depending on the airline.1

 KC-135s have been sent to

the depot for scheduled maintenance every 4 years, with an average stay

of 245 days in fiscal year 1995. Even so, the interval for depot maintenance

is now gradually being extended to 5 years.

Planned Depot Maintenance

Work Has Grown

The planned labor hours needed to complete standard depot maintenance

work on each KC-135 increased by about 6,300 labor hours (36 percent)

between fiscal years 1991 and 1995. In fiscal year 1991, the standard work

package, exclusive of any unplanned work, required about 17,300 labor

hours. In fiscal year 1995, this work package labor hours increased to

23,600 hours. About 24,350 hours are planned for fiscal year 1997. This

growth includes time to apply corrosion preventive compounds, remove

and replace significant portions of each airplane’s wiring, and completely

strip the paint from each airplane.

Unplanned Maintenance Has

Also Grown

Once aircraft structures and assemblies are opened and closely examined

during maintenance, additional repairs or replacements of components

and structures are frequently identified. According to an Air Force analysis

of depot maintenance time for fiscal year 1994, unplanned work on the

KC-135 added an average of 61 days per aircraft to depot maintenance on

the aircraft. Significant portions of the KC-135s’ fuselage skins have had to

be replaced due to corrosion. Also, inspections revealed significant cracks

in major structural components such as fuselage bulkheads and wing

production breaks, which had to be replaced. In 1991, we reported that

unforeseen, unscheduled maintenance accounts for nearly one-half of the

1

Aircraft Maintenance: Additional FAA Oversight Needed of Aging Aircraft Repairs (Vol. I)

(GAO/RCED-91-91A, May 24, 1991).

Page 25 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

heavy airframe maintenance done on commercial aircraft.2 Unscheduled

maintenance increases to about 65 percent on aircraft over 10 years old

and continues to rise as they get older. This situation appears to parallel

the Air Force’s experience in maintaining its older tanker fleet and

suggests that its KC-135 maintenance costs and workload will continue to

rise.

Some Depot Maintenance to Be

Deferred Because of Rising

Cost Estimates

Depot overhauls planned for nine KC-135 tankers during fiscal year 1996

will be deferred to fiscal year 1997 because actual maintenance costs are

higher than budgeted amounts. Depot officials told us that between

submission and execution of the fiscal year 1996 budget (about 

18 months), additional tasks were added to the standard work package,

and hourly labor rates increased by about $10. As a result, AMC will pay

about $18 million more than planned for ongoing overhauls. Consequently,

overhauls of nine aircraft were deferred to adjust for the increase.

Extended Depot

Maintenance Reduces

Tanker Operating

Availability

When the number of KC-135s in depot maintenance exceeds 10 percent or

55 of the 552 current fleet, the squadrons have fewer aircraft than planned

for operations. At any given time, however, about 70 to 90—or an average

of about 15 percent—of the 552 KC-135s are undergoing scheduled

maintenance. In the summer of 1995, 105 aircraft were in the depot—

about twice the number planned for any one time. During our visit to

Fairchild Air Force Base, Washington, 27 percent of the KC-135s were in

depot maintenance.

Air Force Actions to

Improve Aircraft

Availability and Depot

Turnaround Time

The KC-135 System Program Office at the Oklahoma City Air Logistics

Center developed an Aircraft Sustainment Master Plan to identify actions

required to sustain the C/KC-135 fleet. This plan includes efforts to assess

the impact of corrosion on the operational and economic life of the

aircraft.

The master plan cited replacement part shortages as a major cause of

extended depot stays for KC-135s. More than 500 items were identified as

critical to timely support. About 60 percent of these items had not been

authorized for stockage, while the other parts had not been adequately

stocked according to the Air Force. Stock levels of these items were

increased to meet higher parts failure rates occurring due to the age of the

aircraft. Critical items included fuselage skins and major structural

2

Aircraft Maintenance: Additional FAA Oversight Needed of Aging Aircraft Repairs (Vol. I)

(GAO/RCED-91-91A, May 24, 1991).

Page 26 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

components. Outlays for these parts rose from $5.8 million in fiscal 

year 1992, to $70.6 million in fiscal year 1995. The Program Office believes

sufficient parts will be on hand by the end of calendar year 1996 to reduce

depot delays caused by parts shortages.

Lack of information about the condition of aircraft before they arrive at

the depot has also extended depot maintenance time. To remedy this

condition, the Air Force plans to thoroughly inspect each KC-135 about a

year before it is scheduled for depot maintenance to identify the aircraft’s

condition, forecast major parts requirements, and reduce technical

surprises once maintenance begins. A database is being created to track

depot and field maintenance actions and inspection results, including

corrosion information. This will improve the knowledge of each aircraft’s

maintenance history. Currently, there is no specific historical information

available on rework and repairs accomplished on the C/KC-135 fleet.

Costs to Modify

KC-135s Could Be

Substantial

The Air Force could spend over $6.1 billion in the coming years to replace

major structural components and other items to sustain the KC-135 and

improve its reliability, maintainability, and capability. Although many of

these modifications would not be required in a new tanker, most will

probably be made because they will be needed to sustain the KC-135 fleet

over several more decades. Table 2.2 lists these modifications and their

estimated cost. Modifications costing about $1.1 billion have been funded.

Table 2.2: Possible KC-135

Modifications Dollars in millions

Modification Estimated cost

KC-135E engines $3,772.0a

Structural components and aging items 1,717.8

Compass/radar/GPS (PACER CRAG) 386.5b

Multipoint refueling 203.9b

Ground collision avoidance system 19.5b

Automatic communication processor 29.0b

ARC-190 radio 22.3b

Total $6,151.0

aAbout $436 million has been funded to replace engines on 20 aircraft. The Air Force is still

considering whether to replace the engines on 139 additional KC-135Es.

bFunded.

Page 27 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

KC-135E Engine Options

Could Be Costly

Beginning by 2000, the Air Force could spend up to $600 million to

overhaul or up to $3.3 billion to replace the TF33 engines on 139 Air

Reserve Component (ARC) KC-135E tankers to keep them operational and

reduce support costs.3

 The TF33 engines are used, refurbished commercial

engines which, at current usage rates, will need a major overhaul around

the turn of the century. This will include related repairs to cracked and

corroded struts and engine shrouds.

Even if overhauled, the TF33 engines will not meet federal noise and

pollution standards. The Federal Aviation Administration will impose even

more stringent noise standards in 2000. Since many ARC aircraft operate

from commercial airports, they could be subjected to operating hour

restrictions or other penalties that could affect tanker operations and

flexibility.

An option is to replace the TF33s with the CFM-56 engine, which

according to Boeing meets noise and pollution standards, requires less

maintenance, has more thrust, and is more fuel efficient. The increased

thrust enables CFM-56-equipped KC-135s to take off from shorter runways

(increasing basing options) and, when combined with better fuel

efficiency, increases the amount of fuel available for offloading by about

25 percent. The Air Force is conducting a life-cycle cost analysis to

determine the economic payback point for replacing the TF33 engines

with CFM-56 engines. It will use this analysis to determine whether to

modify the remaining ARC aircraft. The average replacement cost per

aircraft is about $24 million.

Multipoint Refueling

Capability Will Enhance

Inter-Service Support

The Air Force plans to spend about $204 million ($33.5 million for

research, development, test, and evaluation, and $170.4 million for

procurement) to modify 45 KC-135s and buy 33 sets of wing refueling pods

to add a “multipoint” capability to enhance cross-service refueling

operations. Currently, the services lack standardized refueling equipment.

When Air Force tankers refuel Air Force receiver aircraft, the boom

operator maneuvers the tip of the tanker’s centerline refueling boom into a

receptacle built into the receiver aircraft’s fuselage. In contrast, Navy,

Marine Corps, and most allied receiver aircraft have a refueling probe that

3

ARC tankers were fitted with the TF33 engine as a low-cost interim measure to improve performance

and operating capability until the state-of-the-art CFM-56 engine could be installed. The Air Force is

currently replacing the TF33 engines on 20 ARC KC-135E aircraft with CFM-56 engines at a cost of

about $436 million. These aircraft represent the last of the KC-135s for which re-engining funds have

been approved. The Air Force estimates that the last four aircraft will be completed in fiscal year 1998.

By the completion of the currently approved program, it will have installed CFM-56 engines on 410

KC-135s.

Page 28 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

the pilot maneuvers into a funnel-shaped drogue basket mounted at the

end of a hose trailing from the tanker. For KC-135s to refuel

probe-equipped receivers, a short hose and basket adapter is added to the

end of the boom before flight. However, with the adapter installed,

KC-135s cannot refuel Air Force aircraft. This current arrangement

complicates mission planning and operations involving both types of

receiver aircraft.

The multipoint modification will alleviate these problems. Two

wing-mounted pods containing a retractable hose and refueling drogue

will be installed on some KC-135s, enabling modified tankers to

simultaneously refuel two probe-equipped Navy, Marine Corps, or allied

aircraft during joint operations. The modified tankers will retain the boom

to refuel Air Force aircraft.

DOD Could Enhance

Operational Flexibility

With a Dual-Role

Tanker/Cargo Aircraft

Although the Air Force has not yet determined the remaining economic

service life of either the C-5A airlifter or the KC-135 tanker, the Air

Mobility Command has placed a higher priority on replacing the C-5A

beginning in fiscal year 2007, while deferring the start of a KC-135

replacement from fiscal year 2007 to 2013. Since procurement of a

commercial-derivative aircraft could take as long as 4 to 6 years and

development of a new military aircraft could take up to 12 years, the Air

Force will need to quickly initiate studies to develop a replacement

strategy for mobility aircraft. We believe that a dual-role cargo/tanker

replacement may satisfy both needs. Current tanker aircraft like the KC-10,

the KC-135, and the KC-130 have already demonstrated the versatility and

value of a dual-role aircraft. They have also shown the viability of using a

commercial design since the KC-10 was derived from the commercial

DC-10 and because both the Boeing-built KC-135 and its commercial 707

were developed from a common design.

AMC, in its 1996 Air Mobility Master Plan (October 1995), which reflects the

Command’s future vision and detailed plans for its total force, expressed

doubts that the KC-135 could continue to operate economically over the

next 25 years, to about 2020, because of corrosion. Although 2020 is a

much shorter period than the 2040 date reflected in the 1995 Air Mobility

Master Plan, AMC deferred the start of the planned KC-135 replacement

from 2007 to 2013. At the same time, it accelerated plans to replace the

C-5A aircraft beginning in 2007. AMC, concerned about the economic life of

the C-5A, cited the airlifter’s high operational and support costs and low

Page 29 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

readiness and reliability as reasons to begin studying a replacement for the

C-5A.

Aging KC-135s will eventually have to be replaced. A replacement tanker

will be expensive—preliminary cost estimates range from about

$100 million to $150 million each—and will compete with other acquisition

programs. However, some Air Force officials indicated that replacement

may be less than one-for-one. Nevertheless, several hundred new aircraft

will have to be procured to replace over 550 KC-135s. If replacement does

not begin until 2013, and only a limited number of new aircraft are

procured annually, many KC-135s will be retained well past 2020. Figure

2.3 shows a tanker force mix projected by AMC if 12 new aircraft were

delivered in 2013, with 18 aircraft delivered each year thereafter. At that

rate, the Air Force would have only 138 new aircraft by 2020, with 

406 KC-135s remaining.

Page 30 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

Figure 2.3: KC-135/Replacement Tanker Force Mix

12 14 16 18 20 22 24 26 28 30 32

0

100

200

300

400

500

600

Fiscal year

Number of aircraft

KC-135 KC(X)

Source: GAO analysis of Air Force data.

The eventual need to replace both KC-135s and C-5As presents the Air

Force with an opportunity to possibly meet air refueling and airlift needs

with a single type of aircraft. A significant portion of the cost to acquire

separate tanker and cargo aircraft might be avoided if the Air Force

considered one type of aircraft capable of filling both airlift and tanker

needs. It has already demonstrated the value, versatility, and feasibility of

dual-mission capability in its KC-10 aircraft. The KC-10 is a swing role

tanker/airlift aircraft that can be used to refuel aircraft and carry cargo

simultaneously, or perform either mission exclusively. It has a 342,000

pound fuel capacity and can be refueled in flight itself, thus extending its

Page 31 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

range and the time it can remain airborne. It can carry 79 passengers and

crew, and up to 170,000 pounds of oversized and bulk cargo. According to

AMC, the KC-10 provides 13 percent of the total U.S. military organic airlift

capacity. In Operations Desert Shield/Desert Storm, KC-10s conducted

over 12,200 air refuelings and offloaded 297.6 million pounds of fuel

(25 percent of the total), carried 53.7 million pounds of cargo, and

transported over 6,700 passengers.

Compelling reasons to consider a joint cargo/tanker aircraft include the

added utility of this combination, airframe commonality, increased

reliability and maintainability, and the reduced operating and maintenance

expenses of modern aircraft. Improved reliability and maintainability

increases the number of aircraft available for operations, thereby

increasing the effectiveness of a smaller force. The operating and support

costs of a modern state-of-the-art aircraft can be far less than the 1950s

vintage KC-135 because, in part, a new aircraft incorporates modern

manufacturing techniques and stronger, more corrosion-resistant and

fatigue-resistant materials.

Conclusion Although the services’ air refueling tanker aircraft meet current needs,

satisfying future requirements may be difficult. The long-term

serviceability of the KC-135 tanker fleet is questionable, as the aircraft are

30 to 40 years old and are taking progressively more time and money to

maintain and operate. Furthermore, the Air Force could spend over

$6 billion in modifications and structural repairs to keep the KC-135 fleet

operational. However, even though the Air Mobility Command doubts that

the KC-135 can be economically operated beyond 2020, it has delayed

consideration of a replacement program until around 2013 because it

considers replacement of the C-5A transport by 2007 a higher priority.

Although service officials say they cannot currently afford to acquire a

new tanker, the Air Force must eventually replace the KC-135. As the Air

Force considers replacing its C-5A, it has an opportunity to enhance

operational flexibility by acquiring a multiuse aircraft that combines

transport and refueling capabilities. The Air Force now plans to buy both a

new transport aircraft to replace its C-5A and a new tanker later to replace

the KC-135. Since tanker aircraft are also used as cargo aircraft, such as in

the case of the KC-10, a dual-use aircraft is a viable option.

Recommendation Because the services have successfully used variants of commercial

aircraft for both air refueling and cargo missions, we believe that a

Page 32 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 2 

The Services Have Deferred Plans to

Replace Aging Tanker Aircraft

dual-use replacement aircraft could fulfill both airlift and air refueling

missions. Accordingly, we recommend that the Secretary of Defense

require that future studies and analyses of replacement airlift and tanker

aircraft consider accomplishing the missions of the C-5A and KC-135 with

a dual-use aircraft that, when combined with C-5Bs, C-17s, and KC-10s,

will meet those requirements. This could eliminate the need to acquire two

aircraft types, one for airlift and the other for refueling.

Agency Comments DOD agreed that future analyses regarding replacement of refueling or

airlift aircraft should include a study of accomplishing the dual mission of

airlift and refueling with one aircraft. However, it was concerned about

how a dual-use aircraft would be used and whether one mission area

might be degraded in order to accomplish the second mission.

Accordingly, it would not commit to a dual-use aircraft until future

analyses are done on operational issues and on the potential performance

of a dual-use aircraft fulfilling both airlift and refueling missions and

meeting deployment and employment requirements.

We agree that future analyses should address operational issues and

whether a dual-use aircraft, used in conjunction with other air mobility

assets, can perform both the airlift and aerial refueling mission, either

separately or concurrently, without jeopardizing either mission. Such

analyses will necessarily encompass a wide range of issues, including the

air mobility requirements for deployment, employment, sustainment, and

redeployment of U.S. forces; current and planned capacity, capability, and

force structure; enroute and in-theater basing and infrastructure; and

reliability, maintainability, and supportability.

Although DOD asserted that there are opposing requirements between the

airlift and refueling missions, the KC-10, through its ability to either

perform each mission exclusively, or perform both missions

simultaneously, has demonstrated the value and flexibility of dual-use

aircraft. We believe that a properly sized force of dual-use replacement

aircraft, used in conjunction with other air mobility assets such as the

C-17s, could meet airlift requirements, while still providing necessary air

refueling. Like the KC-10, that replacement could perform these missions

exclusively or concurrently, depending on the circumstances and

conditions at hand. We believe there are a range of alternative aircraft that

could be considered for a dual-use replacement.

Page 33 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 3 

Peacetime Activities Are Stressing the

Tanker Fleet’s Support Capabilities

With more than half of the Air Force’s KC-135s in its possession, ARC units

augment the active force in war and peacetime, as needed.1

 As the demand

for air refueling has not diminished in proportion to the reduction in the

number of tactical aircraft, the Air Force is increasingly relying on ARC to

provide air refueling for peacetime missions. Because the United States

has been involved in contingency operations in remote areas of the globe,

tanker aircraft are frequently called on to refuel previously

forward-deployed military aircraft as they fly to and from their

destinations and to facilitate and sustain the performance of their mission

once they are in place.2

 Meeting these demands has meant higher

deployment rates for the active force and an increased share of the

refueling workload for ARC. The ARC is able to meet these commitments

through high volunteerism rates. However, the increased peacetime

workload is stretching reserve crews’ availability far beyond the point (38

days) that they are legally required to train.

Increased Peacetime

Activity Results in

High Deployment

Rates for the Active

Force

As the Soviet threat collapsed, the U.S. military faced new operating

realities. Although the overall size of U.S. forces, defense budgets, and

overseas presence have been significantly reduced, U.S. forces continue to

deploy for traditional combat training and to participate in contingency

operations. This has resulted in increased deployments that have stressed

active duty service members who must spend longer temporary duty

assignments away from home.

Since Operations Desert Shield and Storm, the Air Force has asked ARC to

support a number of contingency operations. These contingency

operations include Provide Comfort (northern Iraq), Uphold Democracy

(Haiti), Restore Hope (Somalia), and Deny Flight (Bosnia). In

December 1992, as part of Operation Restore Hope, 381 AFRES volunteers

were placed on active duty for 31 days, flying 190 sorties, airlifting

1,076 passengers and 1,504 tons of cargo, and offloading nearly 1.8 million

pounds of fuel in flight. Similarly, during the last quarter of fiscal year 1994

and the first quarter of fiscal year 1995, ANG provided 1,071 tanker

personnel and 37 aircraft for Deny Flight operations.

1

The ARC comprises the Air National Guard (ANG) and Air Force Reserve (AFRES), created in 1947

and 1948, respectively. Under 10 U.S.C. 10102, ARC members can be mobilized to augment the active

Air Force during a war or national emergency or as the national security may require.

2

Contingency operations are military operations that exceed the routine deployment or stationing of

U.S. forces abroad but fall short of large-scale theater warfare.

Page 34 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 3 

Peacetime Activities Are Stressing the

Tanker Fleet’s Support Capabilities

Air Force officials also told us that the drawdown of U.S. forces from

overseas bases has added to air refueling requirements because of the

need to refuel U.S.-based tactical aircraft to enable them to reach and

return from their overseas destinations and to facilitate their performance

and sustainment of their missions once they are in place. According to AMC

officials, before Operations Desert Shield and Storm, contingency

operations accounted for less than 2 percent of the total air refueling

activity. Since then, these operations have accounted for an average of

more than 20 percent of the mission. In addition, contingency air refueling

directly contributed to actual flying hours exceeding planned flying hours

by an average of 11 percent in the post Desert Shield/Storm era. Figure 3.1

shows the increase in air refueling activity of the European and Pacific

Commands since 1990.3

 Other factors also contributed to the increased air

refueling demand. For example, since the drawdown of U.S. forces, the

F-16 has become the primary fighter aircraft in the European Command.

Because it cannot fly as far as other fighters without being refueled, it is

more dependent on tankers than, for example, was the F-111. Thus, while

fewer fighter aircraft are in the theater, those remaining are more

dependent on tankers than before. In addition, because fewer units are

based in Europe, ongoing missions such as the Bosnian operation require

the periodic rotation and replacement of personnel, equipment, and

supplies, and each trip across the Atlantic requires tanker support.

3

These operating commands are directly affected by the drawdown from overseas bases. In addition, a

number of recent contingency operations have operated from the European Command’s theater of

operations. It should be noted, however, that due to limitations in AMC’s historical tanker reports, the

level of tanker activity occurring in Europe Command’s theater is understated. It includes no tanker

activity of ARC units, or of other commands’ assets temporarily under the operational command of the

Europe Command. Further, tanker activity supporting Southern Watch, an operation directed by

Central Command, is reported by the various participating commands that own the tanker assets

employed in the operation.

Page 35 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 3 

Peacetime Activities Are Stressing the

Tanker Fleet’s Support Capabilities

Figure 3.1: KC-135 Flying Hours in Overseas Commands

90 91 92 93 94

0

2,000

4,000

6,000

8,000

10,000

Fiscal year

Flying hours

Air Force Pacific Air Force Europe

Source: GAO analysis of Air Force data.

Because of the increase in peacetime activity, active duty tanker crews are

spending significant amounts of time on temporary duty away from their

home stations. In February 1995, the Secretary of the Air Force and the

Chief of Staff jointly testified before Congress that active duty personnel

deployments increased four-fold over a 4-year period. In fiscal years 1994

and 1995, the deployment rates for individual tanker crew members,

particularly navigators, approached the 120-day management limit, ranging

from 103 to 117 days, depending on crew position.4

 We recently reported

that, with the exception of the Navy, unit personnel described a variety of

stresses on individuals and families of high-deploying units in the active

4

Currently there is an Air Force-wide shortage of navigators.

Page 36 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 3 

Peacetime Activities Are Stressing the

Tanker Fleet’s Support Capabilities

force, including difficulties in financial management, retention problems,

high divorce rates, substance abuse, and career hardships.5

Reserve Component

Is Performing More

Refueling Missions

To hold the line on active duty deployment rates, the Air Force has

increasingly relied on ARC volunteers to take on more and more of the

workload. In fiscal year 1993, ARC crews flew 27 percent of the total sorties

and 30 percent of the total flying hours flown by ARC and AMC. In fiscal year

1995, ARC flew 44 percent of the total sorties and 49 percent of the total

flying hours flown by ARC and AMC. ARC officials indicated that ARC is

currently operating at about 95 percent of its availability.

Today, ARC maintains more than half of the KC-135 fleet. By the end of

fiscal year 1996, based on congressional direction, the active Air Force will

have transferred about 296, or 54 percent, of the KC-135 tankers to ARC.

With 19 tanker units and 224 aircraft, ANG has the majority of the ARC

tankers; AFRES has 7 tanker units and 72 aircraft. A typical ARC tanker unit

is comprised of a mix of part-time and full-time crews.

During peacetime, DOD may gain access to reservists in two ways. Under

10 U.S.C. 12304, the President may order reservists to serve on active duty

involuntarily. Also, under 10 U.S.C. 12301(d), DOD can activate any

reservist with his or her consent. Unless mobilized, ARC members cannot

be required to serve more than 38 days in prescribed training activities to

meet their service obligations.6

 However, it is not unusual for this largely

part-time force to exceed this minimum training requirement. According to

senior ANG and AFRES officials, traditional part-time reservists can

reasonably expect to serve at least 110 duty days a year. This includes

50 days at the home unit and 60 days a year on deployment (time away

from their jobs and families). According to an ANG training official, air

crew generally train an additional 48 flying and flight training periods, 3

school training days on flight simulators, 1 exercise or deployment lasting

5 to 10 days, and a number of special training days, the length depending

on the type of aircraft. In fiscal year 1994, KC-135 AFRES crews averaged 50

crew days away from the home unit; KC-135 ANG crews averaged 68 crew

days away from the home unit, facilitated by high rates of volunteerism. In

fiscal year 1995, the AFRES crews averaged 57 crew days away, while the

ANG crews averaged 52 crew days away.

5

Military Readiness: A Clear Policy Is Needed to Guide Management of Frequently Deployed Units

(GAO/NSIAD-96-105, Apr. 8, 1996).

6

According to DOD Directive 1215.6, AFRES personnel are required to serve a minimum of 38 training

days a year, and ANG personnel are required to serve a minimum of 39 training days a year.

Page 37 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 3 

Peacetime Activities Are Stressing the

Tanker Fleet’s Support Capabilities

But the availability of individual reservists and reserve units to perform

tanker missions can be limited by many factors. For an individual, these

factors include whether the member has a full- or part-time civilian job,

the nature of the job, and the willingness of the employer to grant time

away from the job. According to the Air Force Reserve Commander’s

Review of 1995, a civilian who is not affiliated with the ARC would work

approximately 221 days a year, leaving 144 days for nonwork activities.

However, a typical air crew member works 221 days at a civilian job and

approximately 100 to 120 days at the reserve job, leaving 24 to 44 days free

time. Fulfilling these reserve duties may necessitate reservists’ using their

personal vacation time. The availability of the traditional Guard air crew

members is also affected by civilian employment limitations, the influence

of economic cycles, and can vary greatly among units. The state of the

local economy and airline hiring directly affect aircrew availability. If

civilian employment is down, part-time crew members without full-time

civilian employment can serve more days in the reserves. When the

economy is booming, and more jobs are available, this personnel resource

is diminished.

The limited availability of ARC personnel also precludes them from

supporting some longer term operations. For example, the Commander,

Central Command, Air Force, requires that all personnel supporting

Operation Southern Watch serve a minimum of 91 days in theater. This

effectively precludes the use of ARC tanker units and personnel because

ARC personnel are generally required to serve on active duty for only a

14-day period.

The Air Force has acknowledged that the limited availability of ARC

personnel affects AMC in terms of contingency response time and

operations tempo. According to the current Air Mobility Master Plan, the

transfer of tanker and airlift aircraft to ARC lengthens AMC’s contingency

response time unless ARC is mobilized. Furthermore, the plan states that

continuing mobility requirements and a high operations tempo will

demand more from AMC active duty personnel, which may contribute to

retention problems in the late 1990s.

Officials Say Active

and Reserve

Assignment Mix

Needs Reevaluation

In a 1994 speech, General Fogelman, the Air Force Chief of Staff,

responded to the question: Are we overtasking our people so they are not

ready for combat? with the following remarks:

Page 38 GAO/NSIAD-96-160 U.S. Combat Air Power
Chapter 3 

Peacetime Activities Are Stressing the

Tanker Fleet’s Support Capabilities

We do not have a hollow force problem . . . we have an OPTEMPO problem. We have some

folks on the road too much . . . One of my challenges is to find ways to spread out the TDY

burden . . . [One way may be to] redistribute some force structure between the Guard or

Reserve and active duty units. . . . But, there is a limit on the amount of volunteerism we

can expect from our citizen-airmen. . . . That’s far too much.”7

Several recent studies have discussed the high operating tempos currently

associated with peacetime operations and use of the ARC to provide relief

to the active duty units. In March 1995, we reported on the stress of high

deployment rates that result from the repeated use of certain active duty

support units’, including specialized Air Force aircraft, extended

participation in multiple and/or large scale peace operations. This also

involved the use of the reserve forces to provide relief. Changing the mix

of active and reserve units was one option suggested to DOD to allow it to

meet the demands of peace operations.8

 A September 1995 Rand report on

Air Force needs appropriate for responding to crises and lesser conflicts,

suggested the option that more of the support forces needed for these

operations be retained by the active component.9

Conclusion As noted earlier, the Air Force Chief of Staff testified that in dealing with

the issue of lowering the time personnel are away from home on

deployment, the Air Force has looked to ARC to relieve active duty units in

more mission areas than ever before. In fiscal year 1995, the reserve fleet

flew almost half of ARC and AMC air refueling flight hours. They were able

to do this because of the high rate of volunteerism. But ARC officials

believe they are at about 95 percent of availability. In the last few years,

ARC has been called upon more and more to support tanker missions of the

active force. However, there may be a practical limit to the workload ARC

can assume, because as the ANG KC-135 Operations Council noted in

April 1995, “the Ops tempo has been sustained at a very high level for the

past few years . . . [and] the ability to surge for other than real world

emergencies is diminished.”

7

“Core Competencies — New Missions: The Air Force in Operations Other Than War”, Gen. Ronald R.

Fogelman, Chief of Staff, United States Air Force, remarks to the American Defense Preparedness

Association Symposium, Washington, D.C., December 15, 1994.

8

Peace Operations: Heavy Use of Key Capabilities May Affect Response to Regional Conflicts

(GAO/NSIAD-95-51, Mar. 8, 1995).

9

An Air Force for Crises and Lesser Conflicts, Carl H. Builder and Theodore Karasik, MR-626-AF, Rand,

Santa Monica, California, 1995.

Page 39 GAO/NSIAD-96-160 U.S. Combat Air Power
Appendix I 

Comments From the Department of Defense

Page 40 GAO/NSIAD-96-160 U.S. Combat Air Power
Appendix I 

Comments From the Department of Defense

Now on pp. 7, 32-33.

Page 41 GAO/NSIAD-96-160 U.S. Combat Air Power
Appendix II 

Air Force and Navy Air Refueling Systems

The Air Force, Navy, and Marine Corps use two different refueling

systems. Air Force fixed-wing aircraft employ a boom/receptacle refueling

system. A telescoping tube, or boom, is mounted near the tanker aircraft’s

tail while the aircraft to be refueled (receiver aircraft) is equipped with a

matching receptacle. During refueling, the receiver aircraft’s pilot

positions the aircraft below and behind the tanker aircraft. The boom

operator aboard the tanker then extends the tip of the boom into the

receiver aircraft’s receptacle. The Air Force originally adopted this system

because its relatively high fuel transfer rate was well suited to refueling

larger aircraft such as the bomber fleet.

In contrast, Navy, Marine Corps, and most allied fixed-wing aircraft as well

as all air-refuelable helicopters (including Air Force helicopters) use a

probe/drogue system. During air refueling, the tanker aircraft trails a

flexible hose that ends in a funnel-shaped drogue basket.1

 To refuel, the

pilot of the receiver aircraft or helicopter approaches the basket and

inserts a pipe (the probe) mounted on the receiver aircraft into the basket.

The Air Force’s KC-135s—the most common tanker—are equipped with

centerline refueling booms. Therefore, boom drogue adapter kits must be

installed on the booms prior to the aircrafts’ takeoff to enable them to

refuel Navy, Marine Corps, and allied probe-equipped aircraft. Thus, to

properly support operations involving mixed groups of Air Force, Navy,

Marine Corps, or allied aircraft, tanker planners must ensure that enough

tankers are provided to offload the amount of fuel needed and that the

tankers are properly configured for the type of aircraft to be refueled. The

KC-135s cannot refuel Air Force or allied receptacle-equipped aircraft

when the adapters are installed. KC-10 tankers are equipped with a single

hose and drogue in addition to their booms and, as a result, can refuel

probe- and receptacle-equipped aircraft on the same mission. In addition,

20 KC-10s are being modified to accept wing-tip mounted pods that allow

the aircraft to refuel two probe-equipped aircraft simultaneously.2

1

The hose is stored on a reel mounted in a wing pod or within the aircraft, depending on the type of

aircraft, when refueling operations are not underway.

2

A total of 15 pod kits will be bought.

Page 42 GAO/NSIAD-96-160 U.S. Combat Air Power
Appendix III 

Locations Visited

During our review, we visited the following locations:

Washington, D.C., Area • Office of the Secretary of Defense

• Office of the Chairman, Joint Chiefs of Staff

• Headquarters, U.S. Air Force

• Office of the Chief of Naval Operations

• Headquarters, Marine Corps

• National Guard Bureau

• Headquarters, Naval Air Systems Command

• Air National Guard Readiness Center

• Commission on Roles and Missions of the Armed Forces

• Institute for Defense Analysis

Eglin Air Force Base,

Florida, Area

• Headquarters, U.S. Air Force Special Operations Command

• 9th Special Operations Squadron

• 20th Special Operations Squadron

Honolulu, Hawaii, Area • Headquarters, U.S. Pacific Command

• Headquarters, U.S. Pacific Air Force

• Headquarters, U.S. Pacific Fleet

• Headquarters, Fleet Marine Force Pacific

• Headquarters, Hawaii Air National Guard

• 203d Air Refueling Squadron

MacDill Air Force Base,

Florida

• Headquarters, U.S. Central Command

• Headquarters, U.S. Special Operations Command

Marine Corps Air Station,

El Toro, California, area

• Headquarters, 3d Marine Air Wing

• Marine Air Group 11

• Marine Air Group 16

• VMGR-352

• VMFA-235

Norfolk, Virginia, Area • U.S. Atlantic Command

• Air Combat Command

• Headquarters, U.S. Atlantic Fleet

• U.S. Naval Air Forces, Atlantic

Page 43 GAO/NSIAD-96-160 U.S. Combat Air Power
Appendix III 

Locations Visited

• Carrier Air Wing Eight

• Carrier Air Wing Seventeen

Scott Air Force Base,

Illinois

• Headquarters, U.S. Transportation Command

• Headquarters, Air Mobility Command

Other Military Commands,

Units, and Activities

• Headquarters, U.S. Air Force, Europe, Ramstein Air Base, Germany

• Headquarters, U.S. Central Air Force, Shaw Air Force Base, South Carolina

• U.S. Naval Air Forces, Pacific, San Diego, California

• Carrier Air Wing Two, San Diego, California

• Oklahoma City Air Logistics Center, Tinker Air Force Base, Oklahoma

• 72d Air Refueling Squadron (Air Force Reserve),

• 722d Air Refueling Wing, March Air Force Base, California

• 92d Air Refueling Wing, Fairchild Air Force Base, Washington

• 108th Air Refueling Wing (Air National Guard), McGuire Air Force Base,

New Jersey

• 163d Air Refueling Group (Air National Guard), March Air Force Base,

California

• 168th Air Refueling Squadron (Air Force Reserve), March Air Force Base,

California

• U.S.S. Mount Whitney

• U.S.S. Theodore Roosevelt

Defense-Related

Companies

• AEL Industries, Inc., East Alton, Illinois

• Boeing Aircraft Company, Seattle, Washington

• Frontier Technology, Inc., Santa Barbara, California

• GE Aircraft Engines, Cincinnati, Ohio

• McDonnell-Douglas Aerospace, Long Beach, California

• McDonnell Aircraft Company, St. Louis, Missouri

• RAND Corporation, Santa Monica, California

• Sargent-Fletcher Company, El Monte, California

Page 44 GAO/NSIAD-96-160 U.S. Combat Air Power
Appendix IV 

Major Contributors to This Report

National Security and

International Affairs

Division Washington,

D.C.

William C. Meredith, Assistant Director

Tim F. Stone, Evaluator-in-Charge

Martha J. Dey, Evaluator

Kenneth W. Newell, Evaluator

Nancy L. Ragsdale, Evaluator (Communications Analyst)

(701041) Page 45 GAO/NSIAD-96-160 U.S. Combat Air Power
Ordering Information

The first copy of each GAO report and testimony is free.

Additional copies are $2 each. Orders should be sent to the

following address, accompanied by a check or money order

made out to the Superintendent of Documents, when

necessary. VISA and MasterCard credit cards are accepted, also.

Orders for 100 or more copies to be mailed to a single address

are discounted 25 percent.

Orders by mail:

U.S. General Accounting Office

P.O. Box 6015

Gaithersburg, MD 20884-6015

or visit:

Room 1100

700 4th St. NW (corner of 4th and G Sts. NW)

U.S. General Accounting Office

Washington, DC

Orders may also be placed by calling (202) 512-6000 

or by using fax number (301) 258-4066, or TDD (301) 413-0006.

Each day, GAO issues a list of newly available reports and

testimony. To receive facsimile copies of the daily list or any

list from the past 30 days, please call (202) 512-6000 using a

touchtone phone. A recorded menu will provide information on

how to obtain these lists.

For information on how to access GAO reports on the INTERNET,

send an e-mail message with "info" in the body to:

info@www.gao.gov

or visit GAO’s World Wide Web Home Page at:

http://www.gao.gov

PRINTED ON RECYCLED PAPER
United States

General Accounting Office

Washington, D.C. 20548-0001

Official Business

Penalty for Private Use $300

Address Correction Requested

Bulk Rate

Postage & Fees Paid

GAO

Permit No. G100