The state of airlift for the U.S. military, despite a decade of the highest continuous demand since World War II, remains good, meeting ongoing demands from the troop drawdown in Iraq, simultaneous surge in Afghanistan, and humanitarian relief following devastating earthquakes in Haiti and Chile early this year. However, the outlook for the next few decades is less certain.

The U.S. Air Force’s Air Mobility Command (AMC) estimates its transport aircraft average some 900 flights a day around the world, moving nearly 2,000 tons of cargo and more than 6,000 passengers. That is an operations tempo (Ops Tempo) that equates to one mobility aircraft taking off every 90 seconds, 24 hours a day, 365 days a year.

Since 9/11, that has amounted to more than 1.2 million sorties transporting some 4.5 million tons of cargo and 12.4 million passengers. In addition, AMC has delivered more than 1.5 billion gallons of fuel in air refueling flights.

AMC’s mobility fleet includes a variety of platforms, but the workhorses are the heavy-lift cargo and tanker aircraft – the C-5 Galaxy, C-17 Globemaster III, C-130 Hercules, KC-10 Extender, and KC-135 Stratotanker. Some of those have been in service for more than half a century, some already are into phased retirement plans – and all have been used far beyond their anticipated annual Ops Tempo during the past decade.

“Global Reach ensures our joint team can deploy, maneuver, and sustain large forces on a global scale. In Iraq and Afghanistan, Air Force mobility assets are central to sustaining the joint and coalition team,” Air Force Deputy Assistant Secretary (Science, Technology and Engineering) Dr. Steven H. Walker told the House Armed Services Committee (HASC) Subcommittee on Terrorism, Unconventional Threats and Capabilities on March 23, 2010.

“On any given day, Air Force C-5s deliver life-saving Mine Resistant Ambush Protected [MRAP] vehicles into theater, C-17s airdrop critical supplies to forward-based ground forces, and C-130s provide tactical airlift to move theater-based personnel and equipment.”

However, the C-5 first entered service in 1970, and the last of AMC’s fleet of 111 still-operational Galaxies was delivered in 1980; only 27 new C-17s remain to be delivered out of a total of 223 ordered by the U.S. Air Force (USAF), the first of which was delivered in 1991; the first KC-10 Extender (air-refueling tanker, but also cargo/personnel transport and medical airlift) was delivered in 1981 and the last (59 operational out of 60 produced for AMC) in 1988. Secretary of Defense Robert Gates recently ordered an end to C-17 production, although Boeing continues to seek new international customers.

The two oldest and most numerous aircraft in the AMC inventory began service more than 50 years ago. The C-130 Hercules, one of the Air Force’smost versatile transports, remains in production, with yearly deliveries since 1956 to the United States and more than 70 other nations and 428 (as of the end of 2009) still in service with the U.S. Air Force, Reserves, and Air National Guard. The first KC-135 Stratotanker was delivered in 1957, the last in 1965; overall, Boeing built 803 Stratotankers between 1954 and 1965 for the USAF, Chile, France, Singapore, and Turkey.

The only new aircraft currently planned for AMC is the KC-X tanker, a controversial program that has been delayed by contracting challenges. A 2008 award to a joint venture by Northrop Grumman and the European consortium EADS for an Airbus A330-based tanker was overturned in 2009, after Boeing filed an appeal challenging the USAF selection process.

The Department of Defense (DoD) briefly reopened bidding in mid-2008, then canceled the solicitation until September 2009, when the Air Force again began accepting new bids. On March 8, 2010, however, Northrop Grumman announced it would no longer participate, adding new turmoil to the program, although the Air Force continues to voice confidence their new tanker soon will be a reality.

“The recent release of a [second] KC-X request for proposal began the process of recapitalizing our aerial refueling aircraft,” USAF Vice Chief of Staff Gen. Carrol H. Chandler told the HASC March 16. “The planned acquisition of 179 KC-X aircraft will help provide refueling capability for decades to come.

“Similarly, the recent release of the Mobility Capabilities Requirements Study-2016 indicates that there is excess strategic airlift capacity. Consequently, the FY 11 budget request proposes the early retirement of 17 of our oldest C-5As.”

In his March 17 report to Congress on the state of TRANSCOM, USAF Gen. Duncan McNabb told the HASC a lot remains to be done to ensure the ability of his command to meet U.S. air mobility demands through the middle of the 21st century.

“Rapid global mobility is critical to TRANSCOM’s quick reaction capability to meet the needs of the joint force and we need to continue recapitalizing our air mobility force,” he told lawmakers. “The ability to extend the range and persistence of almost all other joint force aircraft through air refueling is a distinct asymmetric advantage for our nation – and we need to maintain this advantage. Replacing the KC-135 with the KC-X remains my No. 1 recapitalization priority.

“In addition, KC-135 sustainment and modernizing our aging KC-10 fleet is a necessity, as well. To keep the KC-135 and KC-10 viable assets through 2040 and allow the fleet to operate in the global airspace environment, we must continue to update these aircraft. Strategic airlift is a critical national capability and requires a flexible, capable fleet of inter-theater airlift aircraft. The C-17 has proven its worth of the past eight years in Operations Iraqi Freedom and Enduring Freedom. Its strategic reach and agility in the tactical role have made it an irreplaceable asset. Complementing the C-17, the outsized and oversized cargo capability provided by the C-5 is essential to meeting our global mobility requirements.”

While continuing to modernize the C-5 fleet through the Avionics Modernization Program (AMP) and the Reliability Enhancement and Re-engining Program (RERP), McNabb said the resumption of a C-5 retirement program – delayed for several years by Congress – also is a necessary component of TRANSCOM’s national airlift strategy. At the same time, he anticipates the C-5 and the even older C-130 will remain active and vital parts of U.S. airlift capability for decades to come.

Also critical to that effort, he added, is the new C-27J Spartan Joint Cargo Aircraft (JCA), for which a team comprising L-3 Communications Integrated Systems, Finmeccanica’s Alenia North America, and Global Military Aircraft Systems won a contract in 2007. Already in service with eight nations around the world, the JCA would have been divided between the U.S. Army (54 aircraft) and Air Force (24), but the buy has since been curtailed to 38 aircraft and the program will come under the control of the Air National Guard this year.

“The DoD also requires safe and agile intra-theater airlift and the C-130 continues to be the workhorse of our mobility force operations in Iraq, Afghanistan, and other regions around the world. Fielding the C-27J during the coming year, along with acquisition of the C-130J and modernization of legacy aircraft through the C-130 AMP, will ensure the continued viability of our intra-theater fleet,” McNabb said.

“As the Air Force brings the first C-27Js on line in FY 10, we are confident this new intra-theater asset will provide significant mission-critical/time-sensitive airlift capability in direct support of our joint partners. Its ability to serve in the general and direct support roles will maximize the utility for the warfighter.”

Although far fewer in number and less widely known, AMC’s fleet of Operational Support Airlift and Distinguished Visitor aircraft also are seen asvital air mobility assets, transporting senior military and civilian leaders around the globe.

Each of the primary AMC platforms addresses special air mobility requirements, in some cases each being the only aircraft capable of meeting specific mission needs, in others complementing each other. While much of the fleet is far older than original operational expectations, the projected service life for any aircraft is a combination of multiple factors, including airtime clock hours, number of landings, frequency of flights, mission severity, fatigue, and corrosion.

C-5 GALAXY

The largest aircraft in the Air Force fleet – and one of the largest in the world – the C-5 Galaxy can carry 36 standard cargo pallets and 81 warfighters simultaneously. Or, configured for oversized cargo, the Army’s 74-ton mobile scissors bridge or seven category 1 MRAP vehicles, six AH-64 Apache helicopters, four M2 Bradley Fighting Vehicles, six M1126/M1135 Stryker vehicles or two M1 Abrams main battle tanks from CONUS to any combat theater in the world. It has a maximum cargo capacity of 135 tons and a range of 6,320 nautical miles without refueling, but also has the highest maintenance and operating costs of any U.S. weapons system.

The newest C-5 has now been in service for 21 years and the average fleet age is 40 years, although the Air Force claims a study in the late 1990s showed the fleet at that time had 80 percent of its projected structural service life (50,000-plus hours) remaining. However, demands on the aircraft resulting from post-9/11 military operations worldwide – primarily in Southwest Asia – retirement of the C-141 fleet, and multiple disaster relief efforts across the globe have significantly decreased remaining useful life.

After a brief congressional ban on USAF plans to retire the C-5 in favor of the C-17, a retirement plan was reinstated in 2009, beginning with the C-5As. Even so, the upgraded C-5M variant is expected to remain in service through 2040, at which point the youngest airframe will be at least a half-century old.

C-17 GLOBEMASTER III

The C-17 Globemaster III, with its short landing and take-off airstrip requirements and austere environment capability, has been the primary workhorse of air mobility in Southwest Asia since 9/11. It also has provided support and fast response for numerous humanitarian and disaster relief efforts on every continent, including assisting in the rescue of an icebound British trawler near Antarctica in January 2008.

The C-17 fleet currently has an average age of 7.5 years (137 – about 70 percent – have been delivered in the past 10 years) and is built to meet a contract rate of 1,000 operating hours a year for 30 years. However, the fleet already has logged more than 1.6 million hours and is expected to hit 2 million by the end of 2010 – an average of about 9,300 hours for each aircraft.

Although production for the USAF has been ordered to conclude with delivery of an additional 27 aircraft through September 2012, Boeing also has deliveries scheduled for the United Arab Emirates (four in 2011, two in 2012) and the United Kingdom (its seventh and final delivery in December 2010), as well as options for two additional aircraft for Qatar (which already has taken delivery of two). In addition to those, the C-17 is in operation in Australia (four), Canada (four), and the NATO-led 12-nation Strategic Airlift Capability (three).

Boeing reports that a number of nations, primarily in the Middle East and Europe, continue to express interest in keeping the C-17 line open, but the only prospective new customer to be identified so far is India, which has just opened discussions with the U.S. government about procuring up to 10 C-17s. Boeing believes there is a potential additional international market for 40 to 50 more C-17s.

The company already is in the process of reducing annual production from 15 aircraft to 10, and any new orders would go into production in 2013 and beyond. The question is whether there would be enough orders for delivery quickly enough to maintain a viable production rate.

All new aircraft are Block 18 models, to which older C-17s are being upgraded. Boeing also has proposed an Advanced C-17 (previously designated the C-17B) as an option to meet future airlift requirements. It would feature more powerful engines and an additional main landing gear on the centerline of the fuselage, allowing even shorter runway operations, but the Air Force has not stated a requirement for it.

C-130 HERCULES

The C-130 Hercules has gone through a wide range of model upgrades from the original C-130A, first delivered in December 1956, through the most recent C-130J Super Hercules, which was first deployed in February 1999. The aircraft is still in production by Lockheed Martin, with the most recent delivery to Canada on March 14, 2010 (the first of 17 scheduled through 2012), while Tunisia became the latest customer, ordering two C-130J “stretch” variants in March for delivery in 2013 and 2014.

The U.S. fleet inventory, as of October 2009, showed a mix of models distributed among the USAF active force (145), Air National Guard (181), and Air Force Reserve (102). In all, more than 2,300 Hercules aircraft have been built, with some 40 models and variants in service among more than 70 nations, including most of the Americas and much of Europe, the Middle East, and Africa.

The last of the original A-models was retired from the USAF fleet after Vietnam, but a few remain in service with the Honduran air force. Since the Hercules first went into operation more than 50 years ago, about 15 percent have been lost to crashes or enemy fire, including 70 USAF and U.S. Marine Corps aircraft during the Vietnam War.

The Hercules is the largest and heaviest aircraft ever to land on an aircraft carrier, during a series of tests aboard the USS Forrestal in 1963, but, despite the success of those landings, routine operational carrier use was determined to be too risky. Even so, the Hercules has one of the widest mission ranges of any USAF aircraft, including tactical airlift, aerial tanker, command and control, maritime patrol, special operations, search and rescue, humanitarian relief, staff/VIP transport, reconnaissance, airborne hospital, Arctic and Antarctic support, drone control, electronic warfare, space and missile operations, test and evaluation, weather reconnaissance, and gunship.

The Hercules has a maximum load of up to 44,000 pounds, and can airdrop loads up to 42,000 pounds. Depending on model, its cargo capacity includes the ability to carry up to 128 passengers or 92 airborne troops or up to 97 litter patients with two medical personnel or six to eight cargo pallets, three Humvees or one M113 armored personnel carrier, at ranges varying from 1,250 nautical miles for the C-130E to 2,100 nautical miles for the C-130J-30.

On average, active Air Force C-130 aircraft fly approximately 600 hours per year. The largest fatigue concern to the fleet is the center wing box, which is structurally more susceptible to mission profile and payload stress. It has a limit of 60,000 relative baseline hours (flight hours multiplied by the mission severity factor) and a corrosion limit of 40,000 flight hours, based on historical data and engineering judgment.

The average age of the active-duty C-130 fleet is more than 25 years. Based on projected Ops Tempo and overall mission severity, the Air Force projects its C-130E aircraft have an average remaining service life of 15 years, although a service life extension program (SLEP) and procurement of new aircraft are being employed to resolve some of the Hercules’ aging issues. However, based on current levels of use, the fleet is expected to begin losing airworthiness in 2013.

KC-10 EXTENDER

The KC-10 Extender first entered service in 1981; 64 were produced through 1987 – 60 for the USAF and four for the Royal Netherlands Air Force. As of 2009, the remaining 59 U.S. aircraft in service were operated by the USAF active force; the sole loss resulted from an explosion on the ground during maintenance.

Based on the commercial DC-10, the KC-10 Extender can transport 75 passengers and nearly 170,000 pounds of cargo up to 4,400 miles without refueling. As a tanker, its six fuel tanks have a combined capacity exceeding 356,000 pounds of fuel – almost twice that of the KC-135 – and offers both an advanced aerial refueling boom and a traditional hose-and-drogue centerline system, enabling it to refuel a variety of U.S. and allied aircraft on the same mission, including night operations. The KC-10 also can be refueled in flight itself by a KC-135 or other KC-10A to increase its delivery range.

As one of the newest aircraft in the Air Force inventory, the KC-10 requires little maintenance and modifications compared to older aircraft. Designed with a service life of 30,000 hours, the fleet has a projected structural service life through 2043. While commonalty with its DC-10 commercial counterparts has helped keep operations economical, the largest commercial users already are beginning to retire their DC-10s, leaving smaller airlines as the only remaining civil users, which is expected to negatively affect the cost of future KC-10 operations.

“The KC-10 fleet remains a viable platform through 2040, but it must be modified to ensure the fleet can operate in the future global airspace environment,” Air Force Chief of Staff Gen. Norton Schwartz told the HASC in March 2010. “To this end, AMC has initiated a KC-10 Aircraft Modernization Program that complies with international airspace requirements, addresses obsolescence concerns, and provides a growth path for future avionics upgrades.”

KC-135 STRATOTANKER

The KC-135 military contract in the mid-1950s enabled Boeing to pursue development of the 707, the first commercial jetliner, which changed the face of commercial aviation forever – and enabled Boeing to overtake Douglas Aircraft in commercial production for the first time (Douglas was merged into its military rival, McDonnell Aircraft, a few years later and McDonnell Douglas was absorbed by Boeing in 1997).

Air Mobility Command manages an inventory of more than 415 Stratotankers, of which the Air Force Reserve and Air National Guard fly 235 in support of AMC’s mission. Through its eight-year delivery cycle (1957-65), the Air Force purchased 732 Stratotankers. Another 71 KC-135s were delivered to Chile, France, Singapore, and Turkey.

The KC-135 is one of only six military fixed-wing aircraft with more than half a century of continuous service (along with the Tupolev TU-95, C-130 Hercules, B-52 Stratofortress, English Electric Canberra, and Lockheed U-2).

As maintenance costs increase, the Air Force continues to look at the proposed KC-X to replace the KC-135, but some studies project many of the current fleet could remain in service through 2040, at which point some would be 80 years old. The aircraft already has undergone a number of upgrades and modifications, including two major re-engining programs and significant improvements to its refueling system to meet the needs of new generations of “client” aircraft.

Primarily as a result of operations in Southwest Asia since 9/11, the KC-135 fleet is averaging twice its planned yearly flying hours. Even so, the Air Force estimates the fleet has between 12,000 and 14,000 flying hours each – only 33 percent of their lifetime flying-hour limit. But actual age – already exceeding 40 years – airframe corrosion, and escalating maintenance costs have driven the replacement effort. Due to the large number of Stratotankers still in the fleet, however, some KC-135s are expected to remain in operation for another two or three decades.

The Outlook

“Although our aircraft inventory has seen extensive use in contingency operations and its average age continues to increase, the dedicated work and professionalism of our airmen ensures we are ready,” Chandler said. “After retiring many of our oldest and most maintenance-intensive aircraft – such as all KC-135Es and a fourth of the C-130Es – less than 1 percent of Air Force aircraft are grounded and fewer than 5 percent are flying with operational restrictions.

“The readiness of the mobility air forces remains high while meeting robust and dynamic operational requirements. Our airlift fleet continues to provide strategic airlift as well as theater and direct support airlift missions moving personnel and a wide variety of equipment and supplies. Despite 19 years of sustained Air Force deployments, the personnel and aircraft of the U.S. Air Force are ready to face any challenge with precision and reliability. Although ongoing operations affect a portion of our readiness, we are balancing our force to ensure our personnel, weapon systems, equipment, and organizations are prepared for today’s operations and tomorrow’s uncertain challenges.”

This story was first published in the 2010 Defense Logistics: Supporting the Warfighter supplement to The Year in Defense.